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Title:
NOVEL SINGLE STEP ESTERIFICATION PROCESS OF ALDEHYDES USING A HETEROGENEOUS CATALYST
Document Type and Number:
WIPO Patent Application WO/2016/079759
Kind Code:
A1
Abstract:
The present invention relates to a novel simple, efficient and single-step process for esterification of aldehydes using a heterogeneous catalyst with high yields. More particularly, the present invention relates to a novel simple, efficient and single-step process for esterification of aldehydes using Titanium superoxide with greater than 80% yields.

Inventors:
SUDALAI, Arumugam (National Chemical Laboratory, Dr.Homi Bhabha RoadPune, Pune 8, 411 008, IN)
DEY, Soumen (National Chemical Laboratory, Dr.Homi Bhabha RoadPune, Pune 8, 411 008, IN)
Application Number:
IN2015/050161
Publication Date:
May 26, 2016
Filing Date:
November 10, 2015
Export Citation:
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Assignee:
COUNCIL OF SCIENTIFIC & INDUSTRIAL RESEARCH (Anusandhan Bhawan, Rafi Marg,New Delhi, New Delhi 1, 110 001, IN)
International Classes:
C07D213/80; C07C67/39; C07C201/14; C07C253/30; C07C319/20; C07D211/94; C07D307/88; C07D317/12; C07D333/38
Foreign References:
US20050070744A12005-03-31
US4877898A1989-10-31
Other References:
YOO ET AL: "Copper-catalyzed oxidative esterification of alcohols with aldehydes activated by Lewis acids", TETRAHEDRON LETTERS, PERGAMON, GB, vol. 48, no. 6, 11 January 2007 (2007-01-11), pages 1033 - 1035, XP005827166, ISSN: 0040-4039, DOI: 10.1016/J.TETLET.2006.11.169
REDDY ET AL.: "A Novel Synthesis and Characterization of Titanium Superoxide and its Application in Organic Oxidative Processes", CATAL. SURV. ASIA, vol. 14, 2010, pages 21 - 30, XP002755702
DEY ET AL.: "Titanium superoxide - a stable recyclable heterogeneous catalyst for oxidative esterification of aldehydes with alkylarenes or alcohols using TBHP as an oxidant", ORGANIC AND BIOMOLECULAR CHEMISTRY, vol. 13, 4 September 2015 (2015-09-04), pages 10631 - 10640, XP002755703
K. RAJENDER REDDY ET AL.: "Catalytic oxidative esterification of aldehydes and alcohols using KI-TBHP", SYNTHETIC COMMUNICATIONS: AN INTERNATIONAL JOURNAL FOR RAPID COMMUNICATION OF SYNTHETIC ORGANIC CHEMISTRY, vol. 40, no. 2, 2009, pages 186 - 195, XP002755704
D. TALUKDAR ET AL.: "VO(acac) : An efficient catalyst for the oxidation of aldehydes to the corresponding acids in the presence of aqueous H 0", SYNLETT, vol. 24, 2013, pages 963 - 966
Y. ZHU ET AL.: "Copper-catalyzed methyl esterification reactions via C-C bond cleavage", JOURNAL OF ORGANIC CHEMISTRY, vol. 78, 2013, pages 9898 - 9905
NATHAN A ET AL.: "Conversion of primary alcohols and aldehydes into methyl esters by ruthenium-catalysed hydrogen transfer reactions", SYNTHESIS, 2009, pages 1459 - 1462
K. RAJENDER REDDY ET AL.: "Catalytic oxidative esterification of aldehydes and alcohols using KI-TBHP", SYNTHETIC COMMUNICATIONS: AN INTERNATIONAL JOURNAL FOR RAPID COMMUNICATION OF SYNTHETIC ORGANIC CHEMISTRY, vol. 40, no. 2, 2009, pages 186 - 195
MARINA CAPORASO ET AL.: "Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave-assisted green protocol", BEILSTEIN JOURNAL OF ORGANIC CHEMISTRY, vol. 10, 2014, pages 1454 - 1461
SONDOMOYEE KONIKA MOROMI ET AL.: "Acceptorless dehydrogenative coupling of primary alcohols to esters by heterogeneous Pt catalysts", CATALYSIS SCIENCE AND TECHNOLOGY, vol. 4, 2014, pages 3631 - 3635
MOKHTARY MASOUD ET AL.: "PolyVinylPo lypyrrol idone -Supported Boron Trifluoride (PVPP-BF ); highly efficient catalyst for oxidation of aldehydes to carboxylic acids and esters by H 0", IRANIAN JOURNAL OF CHEMISTRY AND CHEMICAL ENGINEERING, vol. 32, no. 2, 2013, pages 42 - 48
LI, PAN ET AL.: "Copper-catalyzed methyl esterification of aromatic aldehydes and benzoic alcohols by TBHP as both oxidant and methyl source", TETRAHEDRON LETTER, vol. 55, 2014, pages 390
WANG, LIANYUE: "Facile and efficient gold-catalyzed aerobic oxidative esterification of activated alcohols", GREEN CHEMISTRY, vol. 16, 2014, pages 2164
LIU, HONGQIANG ET AL.: "Palladium-catalyzed benzylation of carboxylic acids with toluene via benzylic C-H activation", ORGANIC LETTER, vol. 15, 2013, pages 4098
ROUT SAROJ KUMAR ET AL.: "Copper catalyzed oxidative esterification of aldehydes with alkylbenzenes via cross dehydrogenative coupling", ORGANIC LETTER, vol. 14, 2012, pages 3982
Attorney, Agent or Firm:
REMFRY & SAGAR (Remfry House at the Millenium Plaza, Sector 27 Gurgaon, Gurgaon 9, 122 009, IN)
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Claims:
CLAIMS

1. A novel single step esterification process of aldehydes using heterogeneous catalyst comprising the steps of : a. adding the heterogeneous catalyst to a solution of formula (II) in alcohol or toluene followed by the addition of tert- butyl hydroperoxide; b. stirring reaction mixture of step (a) for alcohols or refiuxing for toluene followed by work-up to afford desired product of formula (I).

2. The process as claimed in claim 1, wherein formula (II) is an aldehyde selected from a group consisting of aromatic, aliphatic, heteroaromatic, α,β-unsaturated aldehydes. 3. The process as claimed in claim 1, wherein formula (I) is ester.

4. The process as claimed in claim 1, wherein said heterogeneous catalyst is Titanium superoxide. 5. The process as claimed in claim 1, wherein stirring of step b is at 25°C for alcohol and 80°C for toluene.

6. The process as claimed in claim 2, wherein formula (II) is selected from the group consisting of aryl or heteroaryl aldehyde.

7. The process as claimed in claim 1, wherein said alcohol is selected from the group consisting of alkyl alcohol, allyl alcohol, benzyl alcohol or propargyl alcohol.

8. The process as claimed in claim 1, yield of said process is greater than 80%.

Description:
NOVEL SINGLE STEP ESTERIFICATION PROCESS OF ALDEHYDES USING A

HETEROGENEOUS CATALYST

FIELD OF THE INVENTION:

The present invention relates to novel single step esterification process of aldehydes using heterogeneous catalyst with high yields. More particularly, the present invention relates to novel single step esterification process of aldehydes using Titanium superoxide. BACKGROUND AND PRIOR ART OF THE INVENTION:

Aromatic esters are important and useful structural elements finding tremendous applications in wide range of fields encompassing solvents, lubricants, plasticizing agents, perfumes, pharmaceuticals, agrochemicals, etc. They are routinely prepared by the Fischer esterification and Mitsunobu reaction or occasionally by Favorskii rearrangement, Baeyer- Villiger oxidation and the Pinner reaction.

In addition, halogen-metal exchange of aryl halides with either carbonmonoxide, ethyl chloroformate or DMF have emerged as alternative methods of their synthesis. However, these methods have several limitations such as the reversibility of the esterification reaction, the use of expensive Pd catalysts, toxic CO gas and variable yields in some cases.

A new strategy involving the direct oxidation of aldehydes to esters under mild conditions has assumed special importance in the synthesis of natural products. This useful transformation generally involves oxidative pathway and often requires more than stoichiometric amounts of oxidants (eg: oxone, Sn0 2 SBA-H 2 0 2 , hypervalent iodine, pyridinium bromide perbromide, V 2 O 5 -H 2 O 2 and acetone cyanohydrin/base) and long reaction times. In addition, some of these reagents are unsatisfactory for aldehydes with electron-withdrawing groups.

U.S. Pat. No. 4877898 discloses process for one step esterification using an intermetallic palladium based catalyst system. It comprises the steps of combining an aldehyde with an alcohol, in the presence of oxygen and in contact with a catalyst having the general formula PdTe a Znd E e

Where, E is one or more metals from the group consisting of group IA, IIA, IVA, VIIB or VIII metals, As or Sb; and a, d and e are from about 0 to 3 with the proviso that at least d or e≠0.

U.S. Pat. No. 4877898 discloses process for producing carboxylic esters. A carboxylic ester is produced in one step in a high yield and with a high selectivity by reacting an aldehyde with an alcohol in the presence of oxygen by using a catalyst comprising (I) palladium, (II) at least one compound selected from the group consisting of lead compounds, thallium compounds and mercury compounds and (III) at least one compound selected from the group consisting of alkali metal compounds and alkaline earth metal compounds. Article titled, "VO(acac) 2 : An efficient catalyst for the oxidation of aldehydes to the corresponding acids in the presence of aqueous H2O2" by D. Talukdar et al. published in Synlett, 2013, 24, pp 963-966 reports VO(acac) 2 catalyzes the oxidation of aromatic and aliphatic aldehydes to the corresponding acids efficiently and selectively in the presence of hydrogen peroxide as an oxidant.

Article titled, "Copper-catalyzed methyl esterification reactions via C-C bond cleavage" by Y. Zhu et al. published in Journal of Organic Chemistry, 2013, 78, pp 9898- 9905 reports a highly effective synthesis of methyl esters from benzylic alcohols, aldehydes, or acids via copper-catalyzed C-C cleavage from tert-butyl hydroperoxide is easily accessible and practical and offers an alternative to the traditional way.

Article titled, "Conversion of primary alcohols and aldehydes into methyl esters by ruthenium-catalysed hydrogen transfer reactions" by Nathan A et al. published in Synthesis, 2009, pp 1459-1462 reports alcohols and aldehydes can be oxidized to the corresponding methyl esters by reaction with methanol in the presence of crotononitrile as a hydrogen acceptor using a catalyst combination of Ru(PPh 3 )3(CO)H 2 with xantphos. Solvents were used toluene or methanol. Article titled, "Catalytic oxidative esterification of aldehydes and alcohols using KI- TBHP" by K. Rajender Reddy et al. published in Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 2009, 40 (2), pp 186-195 reports a simple and mild procedure for the facile oxidative esterification of aldehydes and alcohols using potassium iodide (KI) in combination with tert-butyl hydroperoxide (TBHP) as an external oxidant.

Article titled, "Pd/C-catalyzed aerobic oxidative esterification of alcohols and aldehydes: a highly efficient microwave- assisted green protocol" by Marina Caporaso et al. published in Beilstein Journal of Organic Chemistry, 2014; 10 pp 1454-1461 reports an environmentally friendly microwave-assisted oxidative esterification of alcohols and aldehydes in the presence of molecular oxygen and a heterogeneous catalysis (Pd/C, 5 mol %). Article titled, "Acceptorless dehydrogenative coupling of primary alcohols to esters by heterogeneous Pt catalysts" by Sondomoyee Konika Moromi et al. published in Catalysis Science and Technology, 2014, 4, pp 3631-3635 reports supported platinum catalysts have been studied for the acceptor-free dehydrogenative coupling of primary alcohols to esters in the liquid phase under solvent- free conditions in N 2 at 180 °C. The activity depends on the support material, and Pt-loaded Sn0 2 (Pt/Sn0 2 ) gives the highest activity. Pt/Sn0 2 shows higher activity than various transition metals (Ir, Re, Ru, Rh, Pd, Ag, Co, Ni, Cu) loaded on Sn0 2 . The Pt/Sn0 2 catalyst (1 mol %) selectively converted various primary alcohols to their corresponding esters in moderate to high isolated yield (53-91%). Article titled, "PolyVinylPolyPyrrolidone-Supported Boron Trifluoride (PVPP-BF 3 ); highly efficient catalyst for oxidation of aldehydes to carboxylic acids and esters by H 2 0 2 " by Mokhtary Masoud et al. published in Iranian Journal of Chemistry and Chemical Engineering, 2013, 32, 2, pp 42-48 reports a highly efficient method for the oxidation of aldehydes to carboxylic acids using PolyVinylPolyPyrrolidone supported - Boron Trifluoride (PVPP-BF 3 ) in the presence of 35% hydrogen peroxide has been developed in acetonitrile at 60 °C. This procedure cleanly oxidizes variety of aldehydes to the corresponding carboxylic acids. Oxidative esterification of benzaldehyde utilizing PVPP-BF 3 /H 2 0 2 (35%) is also reported in good to excellent yields in acetonitrile at 60 °C. Article titled, "Copper-catalyzed methyl esterification of aromatic aldehydes and benzoic alcohols by TBHP as both oxidant and methyl source" by Li, Pan et al. published in Tetrahedron Letter, 2014, 55, 390 reports a copper-catalyzed synthesis of methyl esters from aromatic aldehydes in the presence of ieri-butyl hydrogen peroxide (TBHP) via a radical reaction mechanism. TBHP acts not only as an efficient oxidant, but also as a green methyl source in such transformation. Moreover, this method could also be efficiently extended to the methyl esterification of benzylic alcohols.

Article titled, "Facile and efficient gold-catalyzed aerobic oxidative esterification of activated alcohols" by Wang, Lianyue et al. published in Green Chemistry, 2014, 16, pp 2164 reports a facile and efficient methodology for the direct oxidative esterification of alcohols with alcohols catalyzed by NaAuCLj with 95% yields.

Article titled, "Palladium-catalyzed benzylation of carboxylic acids with toluene via benzylic C-H activation" by Liu, Hongqiang et al. published in Organic Letter, 2013, 15, 4098 reports a process for direct benzylation of carboxylic acid with toluene via palladium- catalyzed C-H acyloxylation under 1 atm of oxygen.

Article titled, "Copper catalyzed oxidative esterification of aldehydes with alkylbenzenes via cross dehydrogenative coupling" by Rout Saroj Kumar et al. published in Organic Letter 2012, 14, 3982 reports Copper(II) as the catalyst in a cross dehydrogenative coupling (CDC) reaction for the synthesis of benzylic esters using aldehydes and alkylbenzenes as coupling partners. The literature reports several methods to synthesis of esters which has drawbacks like harsh reaction condition, excess use of bases/acids and alcohols/halides, use of more than stoichiometric amount of oxidants, limited range of substrate scope.

Therefore, it is the need to develop a simple and efficient process to overcome the above drawbacks for esterification of aldehydes.

OBJECTIVE OF THE INVENTION: The objective of the present invention is to provide a simple, efficient and single-step process for esterification of aldehydes using a heterogeneous catalyst with high yields.

Another objective of the present invention is to provide novel single step esterification process of aldehydes using Titanium superoxide.

SUMMARY OF THE INVENTION:

Accordingly, the present invention provides a novel single step esterification process of aldehydes using heterogeneous catalyst comprising the steps of : a. adding the heterogeneous catalyst to a solution of formula (II) in alcohol or toluene followed by the addition of tert- butyl hydroperoxide; b. stirring reaction mixture of step (a) for alcohols or refluxing for toluene followed by work-up to afford desired product of formula (I).

In an embodiment of the present invention, wherein formula (II) is an aldehyde selected from a group consisting of aromatic, aliphatic, heteroaromatic, α,β-unsaturated aldehydes.

In another embodiment of the present invention, wherein formula (I) is ester.

In yet another embodiment of the present invention, wherein said heterogeneous catalyst is Titanium superoxide.

In still an embodiment of the present invention, wherein stirring of step b is at 25 °C for alcohol and 80°C for toluene. In another embodiment of the present invention, wherein formula (II) is selected from the group consisting of aryl or heteroaryl aldehyde.

In yet another embodiment of the present invention, wherein said alcohol is selected from the group consisting of alkyl alcohol, allyl alcohol, benzyl alcohol or propargyl alcohol. In a preferred embodiment of the present invention, wherein yield of said process is greater than 80%. BRIEF DESCRIPTION OF THE DRAWINGS :

Fig. 1: FTIR spectra of Ti superoxide and peroxo intermediate (C)

Fig. 2 Reusability study of the catalyst in the case of 4-nitrobenzaldebyde with methanol DETAILED DESCRIPTION OF THE INVENTION:

The invention will now be described in detail in connection with certain preferred and optional embodiments, so that various aspects thereof may be more fully understood and appreciated.

In view of above, the present invention provides a simple, efficient and single-step process for esterification of aldehydes using a heterogeneous catalyst with high yields.

In an embodiments the present invention provides a simple, efficient and single-step process for esterification of aldehydes using a heterogeneous catalyst comprising the steps of: a. Adding the heterogeneous catalyst to solution of aldehyde of formula (II) in alcohol or toluene followed by the addition of tert- butyl hydroperoxide

(TBHP); b. Stirring reaction mixture of step (a) for alcohols or refluxing for toluene followed by work-up to afford the crude product; c. Purifying the crude product of step (b) gives the desired product of formula (I) in pure form.

The above process is shown below in Scheme 1: H. Cs ,TBHP

ArCHO ArCOg '

OHiPhCH ¾

II

Scheme: 1

In another embodiment, said heterogeneous catalyst is Titanium superoxide.

In still another embodiment, said aldehyde of formula Π is selected from aryl or heteroaryl aldehyde represented in following table 1.

In still another embodiment, said aldehyde of formula II is selected from aromatic, aliphatic, heteroaromatic, α,β-unsaturated aldehydes.

Ti su eroxide

ArCHO

ΤΘΗΡ (2 equsv) 2S °C

Table 1: Ti-catalyzed esterification of aryl aldehydes in alcohol: aldehyde substrate scope

n 4-cyanobenzaldehyde 6 88 o Furfural 8 80

Hp is cinnamaldehyde; time 8 h; yield of Ip is 90%.

In yet another embodiment, said alcohol is selected from alkyl alcohol, allyl alcohol, benzyl alcohol or propargyl alcohol represented in following table 2.

Table 2: Oxidative esterification aldehyde: alcohol scope

In still another embodiment, said aldehyde of formula II is selected from aryl or heteroaryl aldehyde represented in following table 3.

Ti superoxide

(10 wt%)

PhCH 3 (5 equiv)

ArCHO ArC0 2 Bn

(lla-p) TBHR ( 2 et 1 uiv )' 80 ° C (la-p)

Table 3: Ti-catalyzed benzylesterification of aryl aldehydes in toluene: aldehyde substrate scope

g 3- NC>2-benzaldehyde 7 88 h 4-Br-benzaldehyde 8 88 i 3- Br-benzaldehyde 8 90

i 4-Cl-benzaldehyde 7 92 k 3 -Cl-benzaldehyde 7 88

1 4-F-benzaldehyde 8 90 m 4-(CF 3 )-benzaldehyde 7 88 n 4-cyanobenzaldehyde 6 96

0 thiophenecarboxaldehyde 8 92

Hp is cinnamaldehyde; time 6 h; yield of Ip is 88%.

The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

EXAMPLES:

Example 1: Experimental Procedure:

Preparation of Ti-superoxide catalyst:

To a stirred solution of 50% aq. H2O2 (5.98 g, o.l75 mmol) was treated with titanium tetraisopropoxide (Ti(0'Pr)4 (5.0 g, 0.0175 mmol) in anhydrous methanol (50 mL) over 40 min under nitrogen atmosphere with continuous stirring at 25 °C for 2 h. The yellow -colored solid formed was filtered on a sintered funnel, washed thoroughly with anhydrous methanol, and dried under reduced pressure (3 mm Hg) at 25 °C for 1 h to give titanium superoxide 98% yield.

General Procedure for esterification of aldehydes:

In a flame dried flask, aldehyde ( 1 equiv) along with alocohols/ toluene (5 equiv) are taken. Then Ti-superoxide (10 wt%) is added followed by the slow addition of TBHP (2 equiv). Then the reaction mixture is stirred at rt (for alcohols) or refluxed at 80 °C for 6-10 hrs. On completion of the reaction (checked by TLC), it is filtered with ethyl acetate, washed with brine, dried over Na 2 S0 4 and concentrated under reduced pressure, giving the crude product. Then on column chromatographic separation (using pet ether: ethyl acetate= 2.5: 97.5) gives the required product.

Example 2: Preparation of Methyl 3-methylbenzoate:

Yield: 78% colorless gum; IR (CHC1 3 ):684, 815, 897, 976, 1043, 1166, 1239, 1381, 1607, 1682, 1722, 1873, 2496 cm- H NMR (200 MHz, CDC13): 52.41 (s, 3H), 3.91 (s,3H), 7.30-7.34 (m, 2H), 7.81-7.85 (m, 2H); 13 CNMR (50 MHz, CDC13): 621.2, 51.8, 126.7, 128.1, 130.0, 133.5, 137.9, 166.9; Analysis :C 9 Hio0 2 requires C 71.98, H 6.71 found C 71.83, H 6.59 %.

Example 3:

Preparation of Methyl 3,4-dimethoxybenzoate:

Yield: 70%, colorless solid; mp 59 - 61 °C (lit. m.p. 60 °C); IR (CHC1 3 ): 764, 1133,

1271, 1294, 1434, 1514, 1600, 1714 cm-1; l H NMR (200 MHz, CDC1 3 ): 6 3.89 (s, 3H), 3.93 (s, 6H), 6.87 (d, J = 8.36 Hz, 1H), 7.53 (d, J = 1.9 Hz, 1H), 7.66 (dd, I = 1.9, 8.36 Hz, 1H); 13 C NMR (50 MHz, CDC13): 6 51.8, 55.8, 110.2,111.9, 122.6, 123.5, 148.6, 152.9, 166.6; Analysis: Ci 0 Hi 2 O 4 requires C 61.22, H 6.16 found C 61.09, H 6.12 %.

Example 4:

Preparation of Allyl 4-nitrobenzoate:

Yield: 76%, colorless oil; IR (CHC1 3 ): 720, 855,933, 995, 1014, 1048, 1102, 1271, 1319, 1348, 1526, 1608, 1727cm- 1 ; 1 H NMR (200 MHz, CDC13): δ 4.84-4.87 (m, 2H), 5.34 (dd, J= 1.3, 10.4 Hz, 1H), 5.31-5.46 (m, 1H), 5.94-6.13 (m, 1H), 8.21 (d, J= 8.9 Hz,2H), 8.29 (d, J= 8.9 Hz, 2H) ; 13 CNMR (50 MHz, CDC13): δ 66.3, 119.0, 123.5, 130.7, 131.6, 135.5, 150.6, 164.1; Analysis: Ci 0 H 9 NO 4 requires C 57.97, H 4.38, N 6.76 found C 57.78, H 4.19, N 6.59 %. Example 5:

Preparation of Benzyl 4-methoxybenzoate:

Colourless liquid; ! H NMR (400 MHz, CDC13): δ (ppm) 3.82 (s, 3H), 5.33 (s, 2H), 6.90 (d, 2H, J = 8.8 Hz), 7.32-7.39 (m, 3H), 7.43 (d, 2H, J = 7.2 Hz), 8.03 (d, 2H, J = 8.8 Hz); 13 C NMR (100 MHz, CDC13): 6 (ppm) 55.5, 66.5, 113.8, 122.7, 128.2, 128.3, 128.7, 131.9, 136.4, 163.6, 166.3; IR (KBr) 2956, 2927, 2850, 1713, 1606, 1511, 1256, 1167, 1099, 1028, 769, 696 cm- 1 ; Anal, calcd for Ci 5 H 14 0 3 : C 74.36, H 5.82; found C 74.32, H 5.90.

Example 6:

Preparation of Benzyl 3,4-dimethoxybenzoate: Colourless liquid; 1H NMR (400 MHz, CDC13): δ (ppm) 3.90 (s, 3H), 3.91 (s, 3H), 5.33 (s, 2H), 6.86 (d, 1H, J = 8.4 Hz), 7.32-7.39 (m, 3H), 7.43 (d, 2H, J = 8 Hz), 7.56 (m, 1H), S3 7.69-7.72 (m, 1H); 13 C NMR (100 MHz, CDC13): δ (ppm) 56.2, 66.7, 110.4, 112.3, 122.8, 123.9, 128.3, 128.4, 128.8, 136.5, 148.8, 153.3, 166.4; IR (KBr) 2951, 2917, 2849, 1711, 1636, 1270, 1220, 1105, 763 cm- 1 ; Anal, calcd for Ci 6 Hi 6 0 4 : C 70.57, H 5.92; found C 70.51, H 5.88.

Example 7:

Preparation of Benzyl thiophene-2-carboxylate:

Colourless liquid; 1H NMR (400 MHz), CDCI 3 ): δ (ppm) 5.34 (s, 2H), 7.08-7.12 (m,

1H), 7.35-7.44 (m, 5H), 7.55-7.58 (dd, 1 H, J= 1.26, 5.05 Hz), 7.82-7.85 (dd, 1H, dd, J= 1.26, 3.66); 13 C NMR (100 MHz, CDC1 3 ): δ (ppm) 66.0, 127.2, 127.5, 128.6, 128.7, 128.9, 133.8, 134.2, 134.8, 136.2; IR (KBr) 3000, 2971, 1731, 1595, 1201, 1112 cm "1 ; Anal. Calcd for Ci 2 H 10 O 2 S: C 66.03, H 4.62; found C 66.01, H 4.62.

Example 8:

Preparation of Benzyl 4-nitrobenzoate

Yield: 90%; 1.53 g; colorless gum; IR (CHC13, cm-1): υιηαχ 2910, 2828, 1717, 1605, 1523, 1330, 1262, 1128; 1H NMR (200 MHz, CDC13): δ 8.09-8.40 (m, 4H), 7.28-7.52 (m, 5H), 5.40 (s, 2H); 13C NMR (50 MHz, CDC13): δ 164.4, 150.7, 135.5, 135.3, 130.8, 128.8, 128.5, 123.5, 67.6; HRMS (ESI): calc. for [(C14H12N04)H] (M+H) 258.0766, found 258.0760.

Example 9:

Preparation of Benzyl 4-methoxybenzoate:

Yield: 88%; 1.56 g; colorless liquid; IR (CHC13, cm-1): umax 3021, 2937, 1711, 1520, 1125; 1H NMR (200 MHz, CDC13): δ 8.02 (d, J = 9.0 Hz, 2H), 7.19-7.49 (m, 5H), 6.90 (d, J = 9.1 Hz, 2H), 5.33 (s, 2H), 3.86 (s, 3H); 13C NMR (50 MHz, CDC13): δ 166.0, 163.4, 136.3, 131.8, 128.6, 128.1, 122.6, 113.6, 66.4, 55.3; HRMS (ESI): calc. for [(C14H1503)H] (M+H) 243.1021, found 243.1025.

Example 10:

Preparation of Benzyl 4-(methylthio) benzoate : Yield: 79%; 1.3 g; colorless liquid; IR (CHC13, cm-1): urnax 3027, 2953, 2923, 1712, 1307, 1269, 1254, 1162; IH NMR (200 MHz, CDC13): δ 8.08 (dd, J = 8.3, 1.4 Hz, 2H), 7.54 (d, J = 7.3 Hz, 1H), 7.33-7.48 (m, 7H), 5.36 (s, 2H), 1.26 (s, 3H); 13C NMR (50 MHz, CDC13): δ 166.2, 144.4, 136.0, 132.9, 130.1, 129.7, 128.5, 128.3, 128.2, 128.1, 127.8, 66.6, 29.7; HRMS (ESI): calc. for [(C15H1402S)H] (M+H) 259.0793, found 259.0795.

Example 11:

Preparation of Benzyl benzoate:

Yield: 72%; 1.44 g; colorless liquid; IR (CHC13, cm-1): urnax 3021, 2957, 1721, 1600, 1525; 1H NMR (200 MHz, CDC13): δ 8.09 (d, J = 7.1 Hz, 2H), 7.52-7.63 (m, 1H), 7.31-7.51 (m, 7H), 5.38 (s, 2H); 13C NMR (50 MHz, CDC13): δ 166.2, 136.1, 133.0, 129.8, 128.6, 128.4, 128.2, 66.7; HRMS (ESI): calc. for [(C14H1202)H] (M+H) 213.0916, found 213.0919. Example 12:

Preparation of Benzyl 4-fluorobenzoate:

Yield: 92%; 1.7 g; colorless liquid; IR (CHC13, cm-1): umax 3030, 2812, 1725, 1610, 1525, 1101; IH NMR (200 MHz, CDC13): δ 7.98-8.16 (m, 2H), 7.33-7.46 (m, 5H), 7.02-7.17 (m, 1H), 5.34 (s, 2H); 13C NMR (50 MHz, CDC13): δ 167.1, 166.2, 165.3, 164.5, 136.1, 135.9, 132.9, 132.3, 132.2, 130.2, 129.7, 128.6, 128.6, 128.3, 128.2, 128.2, 126.4, 126.4, 115.6, 115.4, 66.8; HRMS (ESI): calc. for [(C14H11F02)H] (M+H) 231.0821, found 231.0825.

Example 13:

Preparation of Benzyl 4-cyanobenzoate:

Yield: 96%; 1.7 g; colorless gum; IR (CHC13, cm-1): vjmax 3011, 2982, 2115, 1717, 1610, 1501; IH NMR (200 MHz, CDC13): δ 8.16 (d, J = 8.7 Hz, 2H) 7.73 (d, J = 8.7 Hz, 2H), 7.33-7.49 (m, 5H), 5.39 (s, 2H); 13C NMR (50 MHz, CDC13): δ 164.6, 135.3, 133.9, 132.1, 130.2, 128.7, 128.6, 128.4, 117.7, 116.6, 67.5; HRMS (ESI): calc. for [(C15H11N02)H] (M+H) 238.0868, found 238.0860.

Example 14:

Preparation of Benzyl 3-nitrobenzoate: Yield: 86%; 1.4 g; colorless liquid; IR (CHC13, cm-1): urnax 2975, 1718, 1512, 1421, 1115, 708; IH NMR (200 MHz, CDC13): δ 8.88 (s, IH), 8.30-8.48 (m, 2H), 7.65 (t, J = 8.0 Hz, IH), 7.43-7.48 (m, 2H), 7.33-7.43 (m, 3H), 5 41 (s, 2H); 13C NMR (50 MHz, CDC13): δ 163.9, 148.0, 135.1, 135.0, 131.6, 129.4, 128.5, 128.4, 128.2, 127.2, 124.3, 67.3; HRMS (ESI): calc. for [(C14H11N04)H] (M+H) 258.0766, found 258.0770.

Example 15:

Preparation of Benzyl 3-bromobenzoate:

Yield: 94%; 1.4 g; colorless liquid; IR (CHC13, cm-1): umax 3100, 2980, 1720, 1421, 1125; IH NMR (200 MHz, CDC13): δ 7.98-8.21 (m, 2H), 7.55-775 (m, IH), 7.38-7.48 (m, 6H), 5.36 (s, 2H); 13C NMR (50 MHz, CDC13): δ 165.0, 135.9, 133.0, 132.6, 129.9, 128.6, 128.1, 122.4, 67.1; HRMS (ESI): calc. for [(C14Hl lBr02)H] (M+H) 291.0021, found 291.0021. Example 16:

Preparation of Benzyl 3-chlorobenzoate:

Yield: 86%; 1.5 g; colorless liquid; IR (CHC13, cm-1): rjmax 3105, 2920, 2810, 1715, 1580, 1417; IH NMR (200 MHz, CDC13): δ 7.96-8.15 (m, 2H), 7.49-7.62 (m, IH), 7.34-7.45 (m, 5H), 5.36 (s, 2H); 13C NMR (50 MHz, CDC13): δ 166.3, 136.1, 133.0, 130.2, 129.8, 128.7, 128.6, 128.4, 128.2, 128.2, 127.9, 66.7; HRMS (ESI): calc. for [(C14H11C102)H] (M+H) 247.0526, found 247.0522.

Example 17:

Preparation of Benzyl 3,4-dimethoxybenzoate:

Yield: 90%; 1.47 g; colorless liquid; IR (CHC13, cm-1): rjmax 2981, 2910, 1711,

1575, 1135, 763; IH NMR (200 MHz, CDC13): δ 7.70 (dd, I = 8.5, 2.1 Hz, IH), 7.56 (d, J = 2.3 Hz, IH), 7.29-7.49 (m, 5H), 6.86 (d, I = 8.2 Hz, IH), 5.34 (s, 2H), 3.93 (s, 3H), 3.92 (s, 3H); 13C NMR (50 MHz, CDC13): δ 165.9, 152.9, 142.2, 136.0, 128.5, 128.2, 128.1, 125.0, 106.9, 106.7, 66.7, 60.8, 56.1; HRMS (ESI): calc. for [(C16H1604)H] (M+H) 273.1127, found 273.1132.

Example 18:

Preparation of Benzyl 3,4,5-trimethoxybenzoate: Yield: 92%; 1.41 g; colorless liquid; IR (CHC13, cm-1): umax 3050, 2911, 1710, 1616, 1400; 1H NMR (200 MHz, CDC13): δ 7.21-7.49 (m, 7H), 5.35 (s, 2H), 3.81-3.96 (m, 9H); 13C NMR (50 MHz, CDC13): δ 165.9, 152.9, 148.4, 136.1, 130.0, 128.4, 128.2, 127.9, 123.5, 122.4, 111.9, 110.0, 66.3, 55.7; HRMS (ESI): calc. for [(C17H1805)H] (M+H) 303.1232, found 303.1232.

Example 19:

Preparation of 1,2-Dibenzyl phthalate :

Yield: 92%; 2.37 g; colorless liquid; IR (CHC13, cm-1): umax 2971, 1811, 1720, 1541, 1410; 1H NMR (200 MHz, CDC13): δ 7.67-7.79 (m, 2H), 7.47-7.58 (m, 2H), 7.27-7.37 (m, 10H), 5.20 (s, 4H); 13C NMR (50 MHz, CDC13): δ 167.1, 135.5, 132.0, 131.0, 129.0,

128.5, 128.4, 128.3, 67.3; HRMS (ESI): calc. for [(C22H1804)H] (M+H) 347.1283, found 347.1285. Example 19:

Preparation of 1,4-Dibenzyl phthate :

Yield: 90%; 2.32 g; colorless liquid; IR (CHC13, cm-1): umax 3071, 2911, 1720, 1611, 1580, 1051; 1H NMR (200 MHz, CDC13): δ 8.07-8.14 (m, 4H), 7.33-7.46 (m, 10H), 5.37 (s, 4H); 13C NMR (50 MHz, CDC13): δ 165.5, 135.7, 134.0, 129.7, 128.7, 128.5, 128.3, 67.1; HRMS (ESI): calc. for [(C22H1804)H] (M+H) 347.1283, found 347.1283.

Example 20:

Preparation of Benzyl cinnamate :

Yield: 80%; 1.4 g; colorless liquid; IR (CHC13, cm-1): v ax 3027, 2983, 2923, 1712, 1617, 1307, 1278, 1162, 805, 767; 1H NMR (200 MHz, CDC13): δ 7.72 (d, J = 16.0 Hz, 1H), 7.28-7.54 (m, 11H), 6.47 (d, J = 16.0 Hz, 1H), 5.24 (s, 2H); 13C NMR (50 MHz, CDC13): δ

166.6, 145.2, 136.1, 134.4, 130.4, 128.9, 128.6, 128.4, 128.2, 118.0, 66.3; HRMS (ESI): calc. for [(C16H1402)H] (M+H) 239.1072, found 239.1075. Example 21:

Preparation of Benzyl acrylate:

Yield: 88%; 2.54 g; colorless liduid; IR (CHC13, cm-1): umax 2931, 2848, 1720, 1621, 1580, 1515, 1421; 1H NMR (200 MHz, CDC13): δ 7.35-7.44 (m, 6H), 6.48 (dd, I = 17.2, 1.7 Hz, 1H), 6.18 (dd, I = 17.3, 10.2 Hz, 1H), 5.87 (dd, I = 10.2, 1.6 Hz, 1H), 5.21 (s, 3H); 13C NMR (50 MHz, CDC13): δ 165.7, 135.8, 130.9, 128.5, 128.3, 128.2, 66.2; HRMS (ESI): calc. for [(C10H10O2)H] (M+H) 163.0759, found 163.0760.

Example 22:

Preparation of Benzyl (E)-but-2-enoate:

Yield: 88%; 2.21 g; colorless liquid; IR (CHC13, cm-1): rjmax 3010, 2971, 2882, 1725, 1652, 1568, 1312; 1H NMR (200 MHz, CDC13): δ 7.34 (s, 5H), 6.89-7.13 (m, 1H), 5.80-5.98 (m, 1H), 5.16 (s, 2H), 1.89 (dd, J = 6.88, 1.7 Hz, 3H); 13C NMR (50 MHz, CDC13): δ 166.1, 145.0, 136.3, 128 6, 128.2, 128.2, 122.7, 66.0, 18.1; HRMS (ESI): calc. for [(C11H1202)H] (M+H) 177.0916, found 177.0910.

Example 23:

Preparation of Benzyl propionate:

Yield: 90%; 2.51 g; colorless liquid; IR (CHC13, cm-1): rjmax 2958, 2934, 2839, 1713, 1606, 1511, 1462, 1373, 1258, 1167, 1098, 1029, 847, 769, 741, 721; 1H NMR (200 MHz, CDC13): δ 7.32-7.36 (m, 6H), 5.11 (s, 2H), 2.37 (q, J = 7.3 Hz, 2H), 1.16 (t, J = 7. 6 Hz, 3H); 13C NMR (50 MHz, CDC13): δ 166.2, 136.1, 133.0, 129.8, 128.5, 128.4, 128.2, 66.7, 27.6, 9.2; HRMS (ESI): calc. for [(C10H12O2)H] (M+H) 165.0916, found 165.0917. Example 24:

Preparation of Benzyl thiophene-3-carboxylate:

Yield: 92%; 1.79 g; colorless liquid; IR (CHC13, cm-1): rjmax 3027, 2923, 1712, 1524, 1417, 1374, 1356, 1273,1258, 1094; 1H NMR (200 MHz, CDC13): δ 7.77-7.95 (m, 1H), 7.50-7.65 (m, 1H), 7.32-7.48 (m, 5H), 7.06-7.18 (m, 1H), 5.34 (s, 2H); 13C NMR (50 MHz, CDC13): δ 161.9, 135.9, 134.0, 133.8, 133.6, 132.4, 128.6, 128.3, 128.2, 127.9, 127.7, 66.7; HRMS (ESI): calc. for [(C12H10O2S)H] (M+H) 219.0480, found 219.0490.

Example 25:

Preparation of Benzyl nicotinate:

Yield: 90%; 1.79 g; colorless gum; IR (CHC13, cm-1): rjmax 3102, 2987, 2897, 1720,

1624, 1528, 1325, 1014; 1H NMR (200 MHz, CDC13): δ 9.26 (s, 1H), 8.77 (d, J = 3.5 Hz, 1H), 8.31 (dt, J = 8.0, 2.0 Hz, 1H), 7.25-7.50 (m, 6H), 5.39 (s, 2H); 13C NMR (50 MHz, CDC13): δ 164.9, 153.4, 151.0 137.1, 135.5, 128.7, 128.5, 128.3, 126.0, 123.2, 67.1; HRMS (ESI): calc. for [(C13H11N02)H] (M+H) 214.0868, found 214.0873. Example 26:

General experimental procedure for the preparation of methyl esters:

In an oven dried round bottom flask, 4-nitrobenzaldehyde la (1 g, 6.61 mmol) and Titanium superoxide catalyst (0.1 g, 10 wt%) in dry MeOH (1.32 mL, 33.05 mmol) was added TBHP in decane (5-6 M) (2.4 mL, 13.22 mmol) in a dropwise manner under nitrogen atmosphere. Then the flask was stirred at 25 oC for 6 h. After complete disappearance of aldehyde (judged by TLC; using DNP solution), the reaction mixture was filtered through sintered funnel using CH2C12 as eluent. Then the organic layer was extracted with CH2C12, dried over anhydrous Na2S04, and evaporated under reduced pressure. The crude product was purified by column chromatography over silica (230-400 mesh) using petroleum ether/ ethyl acetate (19: 1 v/v) as eluent to give methyl 4-nitrobenzoate.

Example 27:

Preparation of Methyl 4-nitrobenzoate:

Yield: 88%; 1.0 g; colorless liquid; IR (CHC13, cm-1): vjmax 2810, 1718, 1620, 1524, 1105; 1H NMR (200 MHz, CDC13): δ 8.24 (m, 4H), 3.97 (s, 3 H); 13C NMR (50 MHz, CDC13): δ 164.9, 150.3, 135.3, 130.5, 123.3, 52.6; HRMS (ESI): calc. for [(C8H7N04)H] (M+H) 182.0453, found 182.0455.

Example 28:

Preparation of Methyl-4-methoxybenzoate:

Yield: 82%; 1.0 g; colorless solid; mp.: 49-51 oC (lit.4k mp. 49 oC); IR (CHC13, cm- 1): umax 3050, 2980, 2910, 1716, 1615, 1548, 1258; 1H NMR (200 MHz, CDC13): δ 7.98 (d, J = 8.8 Hz, 2H), 6.90 (d, J = 8.8 Hz, 2H), 3.87 (s, 3H), 3.86 (s, 3H); 13C NMR (50 MHz, CDC13): δ 166.5, 163.2, 131.5, 122.6, 113.5, 55.2, 51.7; HRMS (ESI): calc. for [(C9H10O3)H] (M+H) 167.0708, found 167.0710.

Example 29:

Preparation of Methyl 4-(methylthio)benzoate :

Yield: 82%; 0.98 g; colorless liquid; IR (CHC13, cm-1): umax 2920, 1718, 1658, 1541, 1325, 1258; 1H NMR (200 MHz, CDC13): δ 7.86-8.02 (m, 2H), 7.16-7.33 (m, 2H), 3.90 (s, 3H), 2.52 (s, 3H); 13C NMR (50 MHz, CDC13): δ 166.5, 145.2, 129.5, 125.9, 124.5, 51.7, 14.4; HRMS (ESI): calc. for [(C9H10SO2)H] (M+H) 183.0480, found 183.0485. Example 30:

Preparation of Methyl-4-chlorobenzoate:

Yield: 90%; 1.09 g; colorless gum; IR (CHC13, cm-1): rjmax 2952, 2937, 1725, 1613, 1548, 1256; 1H NMR (200 MHz, CDC13): δ 7.97 (d, J = 8.5 Hz, 2H), 7.41 (d, J = 8.6 Hz, 2H), 3.92 (s, 3H); 13C NMR (50 MHz, CDC13): δ 165.9, 139.3, 130 9, 128 6, 52.1 ; HRMS (ESI): calc. for [(C8H7C102)H] (M+H) 171.0213, found 171.0215.

Example 31:

Preparation of Methyl 4-(trifluoromethyl)benzoate :

Yield: 88%; 1.03 g; colorless gum; IR (CHC13, cm-1): rjmax 2972, 1725, 1657, 1585, 1158; 1H NMR (200 MHz, CDC13): δ 8.14 (m, J = 8.2 Hz, 2H), 7.70 (m, J = 8.2 Hz, 2H), 3.95 (s, 3H); 13C NMR (50 MHz, CDC13): δ 165.5, 135.7, 135.4, 134.7, 134.1, 133.3, 132.5, 129.9, 128.0, 126.2, 125.4, 125.3, 125.2, 125.1, 120.8, 52.3; HRMS (ESI): calc. for [(C9H7F302)H] (M+H) 205.0476, found 205.0475.

Example 32:

Preparation of Methyl-4-cyanobenzoate:

Yield: 90%; 1.13 g; colorless gum; IR (CHC13, cm-1): rjmax 2974, 2225, 1725, 1658, 1425, 1121 ; 1H NMR (200 MHz, CDC13): δ 8.14 (d, J = 8.5 Hz, 2H), 7.75 (d, J = 8.6 Hz, 2H), 3.96 (s, 3H); 13C NMR (50 MHz, CDC13): δ 165.1, 133.9, 132.1, 130.1, 117.7, 116.5, 52.6; HRMS (ESI): calc. for [(C9H7N02)H] (M+H) 162.0555, found 162.0559.

Example 33:

Preparation of Methyl 3-nitrobenzoate:

Yield: 86%; 1.03 g; colorless solid; mp. 78-80 oC (lit.4k mp. 78 oC); IR (CHC13, cm- 1): 2857, 1722, 1620, 1587, 1232; 1H NMR (200 MHz, CDC13): δ 8.81 -8.87 (m, 1H), 8.34- 8.44 (m, 2H), 7.61-7.69 (m, 1H), 3.99 (s, 3H); 13C NMR (50 MHz, CDC13): δ 164.6, 148.2, 135.1, 131.8, 129.5, 127.2, 124.4, 52.6; HRMS (ESI): calc. For [(C8H7N04)H] (M+H) 182.0453, found 182.0455.

Example 34:

Preparation of Methyl 3-bromobenzoate: Yield: 88%; 1.02 g; colorless gum; IR (CHC13, cm-1): umax 2910, 1722, 1590, 1257, 1187; 1H NMR (200 MHz, CDC13): δ 8.16 (s, 1H), 7.95 (d, J = 9.2 Hz, 1H), 7.67 (d, J = 8.0 Hz, 1H), 7.27-7.36 (m, 1H), 3.92 (s, 3H); 13C NMR (50 MHz, CDC13): δ 165.4, 135.7, 132.6, 132.0, 129.8, 128.1, 122.4, 52.2; HRMS (ESI): calc. for [(C8H7Br02)H] (M+H) 214.9708, found 214.9708.

Example 35:

Preparation of Methyl 3-chlorobenzoate:

Yield: 90%; 1.09 g; colorless gum; IR (CHC13, cm-1): umax 2910, 1728, 1535, 1283, 1125; 1H NMR (200 MHz, CDC13): δ 8.00 (t, J = 1.8 Hz, 1H), 7.90 (dt, J = 7.7, 1.3 Hz, 1H), 7.47-7.56 (m, IH), 7.38 (d, J = 7.7 Hz, 1H), 3.92 (s, 3H); 13C NMR (50 MHz, CDC13): δ 165.5, 134.5, 132.8, 131.8, 129.5, 127.6, 52.2; HRMS (ESI): calc. for [(C8H7C102)H] (M+H) 171.0213, found 171.0215. Example 36:

Preparation of Methyl-3,4-dimethoxybenzoate :

Yield: 86%; 1.0 g; colorless liquid; IR (CHC13, cm-1): umax 3110, 2911, 1715, 1625, 1368, 1152; IH NMR (200 MHz, CDC13): δ 7.66 (dd, J = 8.5, 1.9 Hz, IH), 7.53 (d, J = 1.8 Hz, IH), 6.87 (d, J = 8.3 Hz, IH), 3.93 (s, 6H) 3.89 (s, 3H); 13C NMR (50 MHz, CDC13): δ 166.6, 152.9, 148.6, 123.4, 111.9, 110.2, 55.8, 51.8; HRMS (ESI): calc. for [(C10H12O4)H] (M+H) 197.0814, found 197.0815.

Example 37:

Preparation of Methyl-3,4,5-trimethoxybenzoate:

Yield: 84%; 0.96 g; colorless solid; mp. 82-85 oC (lit.4k mp. 82 oC); IR (CHC13, cm-

1): umax 2991, 1720, 1547, 1180; IH NMR (200 MHz, CDC13): δ 7.28 (s, 2H), 3.89-3.93 (m, 12H); 13C NMR (50 MHz, CDC13): δ 166.4, 152.9, 142.1, 125.0, 106.8, 60.7, 56.1, 52.1; HRMS (ESI): calc. for [(C11H1405)H] (M+H) 227.0919, found 227.0920. Example 38:

Preparation of Dimethyl terephthalate:

Yield: 88%; 1.27 g; colorless liquid; IR (CHC13, cm-1): umax 3012, 2987, 1725, 1645, 1058; IH NMR (200 MHz, CDC13): δ 7.77 (d, J = 8.3 Hz, 2H), 7.33 (d, J = 8.0 Hz, 2H), 3.74 (s, 3H), 2.46 (s, 3H); 13C NMR (50 MHz, CDC13): δ 166.8, 144.7, 132.7, 128.0, 56.0; HRMS (ESI): calc. for [(C10H10O4)H] (M+H) 195.0657, found 195.0650.

Example 39:

Preparation of Methyl cinnamate:

Yield: 76%; 0.93 g; colorless gum; IR (CHC13, cm-1): rjmax 1H NMR (200 MHz, CDC13): δ 7.71 (d, J = 16.0 Hz, 1H), 7.48-7.59 (m, 2H), 7.35-7.44 (m, 3H), 6.46 (d, J = 16.0 Hz, 1H), 3.82 (s, 3H); 13C NMR (50 MHz, CDC13): δ 167.3, 144.8, 134.3, 130.2, 128.8, 128.0, 117.7, 51.6; HRMS (ESI): calc. for [(C10H10O2)H] (M+H) 163.0759, found 163.0760.

Example 40:

Preparation of Methyl acrylate:

Yield: 70%; 1.07 g; colorless liquid; IR (CHC13, cm-1): rjmax 1720, 1621, 1569, 1428, 1 104; 1H NMR (200 MHz, CDC13): δ 6.40 (dd, J = 17.2, 1.7 Hz, 1H), 6.11 (dd, J = 17.2, 10.3 Hz, 1H), 5.81 (dd, J = 10.3, 1.7 Hz, 1H), 3.75 (s, 3H),; 13C NMR (50 MHz, CDC13): δ 166.2, 130.3, 127.9, 51.2; HRMS (ESI): calc. for [(C4H602)H] (M+H) 87.0446, found 87.0445. Example 41:

Preparation of Methyl (E)-but-2-enoate:

Yield: 72%; 1.02 g; colorless liquid; IR (CHC13, cm-1): rjmax 1725, 1652, 1590, 1442, 1236; 1H NMR (200 MHz, CDC13): δ 6.98 (dd, J = 15.6, 6.9 Hz, 1H), 5.85 (dd, J = 15.5, 1.6 Hz, 1H), 3.72 (s, 3H), 1.88 (dd, J = 6.9, 1.7 Hz, 3H); 13C NMR (50 MHz, CDC13): δ 166.3, 144.1, 121.9, 50.7, 17.3; HRMS (ESI): calc. for [(C5H802)H] (M+H) 101.0603, found 101.0609.

Example 42:

Preparation of Methyl thiophene-2-carboxylate:

Yield: 88%; 1.11 g; colorless liquid; IR (CHC13, cm- 1): rjmax 2912, 1725, 1645,

1560, 1512, 1464, 1237; 1H NMR (200 MHz, CDC13): δ 7.81 (d, J = 3.0 Hz, 1H), 7.56 (d, J = 4.6 Hz, 1H), 7.1 1 (t, J = 4.3 Hz, 1H), 3.90 (s, 3H); 13C NMR (50 MHz, CDC13): δ 162.5, 133.4, 133.3, 132.2, 127.6, 77.6, 76.4, 52.0; HRMS (ESI): calc. for [(C6H6S02)H] (M+H) 143.0167, found 143.0169. Example 43:

Preparation of Methyl nicotinate:

Yield: 86%; 1.10 g; colorless gum; IR (CHC13, cm-1): umax 3011, 2987, 1718, 1625, 1485, 1201, 1101, 748; 1H NMR (200 MHz, CDC13): δ 9.22 (m, 1H), 8.77 (m, 1H), 7.39 (m, 1H), 8.29 (m, 1H), 3.95 (s, 3H); 13C NMR (50 MHz, CDC13): δ 165.6, 153.3, 150.7, 136.9, 125.8, 123.1, 52.2; HRMS (ESI): calc. for [(C7H7N02)H] (M+H) 138.0555, found 138.0559. Example 44:

Preparation of Dioctyl phthalate:

To a well-stirred solution of phthaldialdehyde (lr) (100 g, 0.745 mol) in dry CH3CN (1000 mL), 1-octanol (194.18 g, 1.491 mol) and titanium superoxide (10 g) were added. Then TBHP in decane (5-6 M) (542.56 mL, 2.98 mol) was added to the reaction mixture in a dropwise manner and kept stirring at 25 oC for 6 h. After the reaction (checked by TLC), the reaction mixture was filtered off through sintered funnel. Then the organic layer was extracted with CH2C12, dried over anhydrous Na2S04, and evaporated under reduced pressure. The crude product was purified by column chromatography over silica (230-400 mesh) using petroleum ether/ ethyl acetate (19: 1 v/v) as eluent to give desired dioctyl phthalate (3r). Yield: 96%; 279.53 g; IR (CHC13, cm-1): umax 3112, 1720, 1621, 1580, 1460, 1150, 1012, 845; 1H NMR (200 MHz, CDC13): δ 7.46-7.60 (m, 2H), 4.28 (t, J = 6.7 Hz, 4H), 1.62-1.90 (m, 5H), 1.22-1.44 (m, 22H), 0.85-0.93 (m, 6H); 13C NMR (50 MHz, CDC13): δ 167.4, 132.4, 130.7, 128.8, 65.7, 31.8, 29.2, 29.2, 28.6, 26.0, 22.6, 14.1; HRMS (ESI): calc. for [(C24H3804)H] (M+H) 391.2848, found 391.2840.

Example 45:

General experimental procedure for the preparation of esters:

In an oven dried round bottom flask, benzaldehydes (1 equiv), alcohols or alkylbenzenes (1 equiv) and Titanium superoxide catalyst (0.1 g, 10 wt%) in dry CH 3 CN (10 mL) was added TBHP in decane (2 or 3 equiv) in a dropwise manner. Then the flask was stirred at 25 °C or heated at 80 °C. After complete disappearance of aldehyde (judged by TLC), the reaction mixture was filtered through sintered funnel using CH2C12 as eluent. Then the organic layer was extracted with CH 2 CI 2 , dried over anhydrous Na 2 S0 4 , and evaporated under reduced pressure. The crude product was purified by column chromatography over silica (230-400 mesh) using petroleum ether/ ethyl acetate (19: 1 v/v) as eluent to give corresponding esters.

Example 45:

Preparation of 4-nitrophenyl 4-methoxybenzoate:

Yield: 70%; 1.47 g; colorless gum; IR (CHC13, cm-1): umax 3105, 2985, 1714, 1637, 1549, 1275, 812; 1H NMR (200 MHz, CDC13): δ 8.25 (d, J = 8.7 Hz, 2H), 8.03 (d, J = 8.8 Hz, 2H), 7.59 (d, J = 8.7 Hz, 2H), 6.93 (d, J = 8.9 Hz, 2H), 5.42 (s, 2H), 3.88 (s, 3H); 13C NMR (50 MHz, CDC13): δ 163.8, 156 0, 148.4, 143.6, 136.6, 131.9, 128.3, 123.9, 113.8, 64.9, 55.4; HRMS (ESI): calc. for [(C15H13N05)H] (M+H) 288.0872, found 288.0875.

Example 46:

Preparation of 1-phenylethyl 3-nitrobenzoate:

Yield: 88%; 1.57 g; colorless liquid; IR (CHC13, cm-1): rjmax 3015, 2985, 2910, 1718, 1642, 1587, 1235, 1148; 1H NMR (200 MHz, CDC13): δ 8.88 (t, J = 1.8 Hz, 1H), 8.33- 8.47 (m, 2H), 7.64 (t, J = 8.0 Hz, 1H), 7.28-7.51 (m, 5H), 6.16 (q, J = 6.6 Hz, 1H), 1.72 (d, J = 6.7 Hz, 3H); 13C NMR (50 MHz, CDC13): δ 163.5, 148.3, 140.9, 135.2, 132.3, 129.5, 128.7, 128.2, 127.3, 126.1, 124.5, 74.1, 22.2; HRMS (ESI): calc. for [(C15H13N04)H] (M+H) 272.0923, found 272.0926.

Example 47:

Preparation of Benzhydryl 3-nitrobenzoate:

Yield: 88%; 1.94 g; colorless liquid; IR (CHC13, cm-1): rjmax 3120, 3050, 1717, 1630, 1545, 1289, 1110; 1H NMR (200 MHz, CDC13): δ 8.82-9.02 (m, 1H), 8.31-8.48 (m, 2H), 7.62 (t, J = 7.9 Hz, 1H), 7.39-7.44 (m, 4H), 7.32-7.38 (m, 4H), 7.26-7.32 (m, 2H), 7.14 (s, 1H); 13C NMR (50 MHz, CDC13): δ 163.3, 148.4, 139.5, 135.3, 132.1, 129.6, 128.7, 128.3, 127.5, 127.2, 124.7, 78.4; HRMS (ESI): calc. for [(C20H15NO4)H] (M+H) 334.1079, found 334.1082. Example 48:

Preparation of 4-methylbenzyl 3-nitrobenzoate:

Yield: 90%; 1.61 g; colorless liquid; IR (CHC13, cm-1): rjmax 3012, 2950, 1718, 1655, 1584, 1431, 1165; 1H NMR (200 MHz, CDC13): δ 8.86 (t, J = 1.8 Hz, 1H), 8.29-8.48 (m, 2H), 7.63 (t, I = 8.0 Hz, 1H), 7.29-7.45 (m, 2H), 7.14-7.26 (m, 2H), 5.36 (s, 2H), 2.37 (s, 3H); 13C NMR (50 MHz, CDC13): δ 164.2, 148.3, 138.5, 135.3, 132.3, 132.1, 129.4, 128.7, 127.4, 124.7, 67.6, 21.3; HRMS (ESI): calc. for [(C15H13N04)H] (M+H) 272.0923, found 272.0920. Example 49:

Preparation of 3-methylbenzyl 3-nitrobenzoate:

Yield: 88%; 1.57 g; colorless liquid; IR (CHC13, cm-1): rjmax 3050, 2965, 1718, 1650, 1580, 1480, 1257, 1106; 1H NMR (200 MHz, CDC13): δ 8.85 (t, J = 1.9 Hz, 1H), 8.37 (dt, J = 8.0, 2.0 Hz, 2H), 7.62 (t, J = 8.0 Hz, 1H), 7.19-7.33 (m, 3H), 7.08-7.18 (m, 1H), 5.35 (s, 2H); 13C NMR (50 MHz, CDC13): δ 164.1, 148.3, 138.3, 135.2, 135.1, 131.9, 129.5, 129.3, 129.2, 128.6, 127.3, 125.6, 124.6, 67.6, 21.4; HRMS (ESI): calc. for [(C15H13N04)H] (M+H) 272.0923, found 272.0925.

Example 50:

Preparation of 3,5-dimethylbenzyl 3-nitrobenzoate:

Yield: 92%; 1.73 g; colorless liquid; IR (CHC13, cm-1): rjmax 3140, 2980, 1720, 1620, 1580, 1465, 1290, 1108; 1H NMR (200 MHz, CDC13): δ 8.88 (t, J = 1.8 Hz, 1H), 8.33- 8.56 (m, 2H), 7.65 (t, J = 8.0 Hz, 1H), 6.92-7.15 (m, 3H), 5.34 (s, 2H), 2.36 (s, 6H); 13C NMR (50 MHz, CDC13): δ 164.1, 148.3, 138.2, 135.2, 135.0, 132.0, 130.2, 129.4, 127.3, 126.4, 124.6, 67.6, 21.2; HRMS (ESI): calc. for [(C16H15N04)H] (M+H) 286.1079, found 286.1075.

Example 51:

Preparation of Ethyl 4-nitrobenzoate:

Yield: 80%; 1.03 g; colorless solid; mp. 97-99 oC (lit.4p mp. 97-98 oC); IR (CHC13, cm-1): umax 3102, 3010, 2950, 1724, 1620, 1580, 1456, 1140, 1011; 1H NMR (200 MHz, CDC13): δ 8.30 (d, J = 8.9 Hz, 2H), 8.21 (d, I = 8.9 Hz, 2H), 4.43 (q, I = 7.3, 14.6 Hz, 2H), 1.44 (t, J = 7.4 Hz, 3H); 13C NMR (50 MHz, CDC13): δ 164.4, 150.5, 135.8, 130.6, 123.5, 61.9, 14.2; HRMS (ESI): calc. for [(C9H9N04)H] (M+H) 196.0610, found 196.0615.

Example 52:

Preparation of Isopropyl-4-nitrobenzoate:

Yield: 78%; 1.07 g; colorless solid, mp.: 105-108 oC (lit.4p mp. 105-106 oC); IR (CHC13, cm-1): rjmax 3112, 2980, 1713, 1620, 1509, 1480, 1253, 1120; 1H NMR (200 MHz, CDC13): δ 8.27 (d, J = 8.5 Hz, 2H), 8.19 (d, J = 8.5 Hz, 2H), 5.24-5.33 (m, IH), 1.40 (d, J = 6.1 Hz, 7H); 13C NMR (50 MHz, CDC13): δ 164.1, 150.3, 136.2, 130.5, 123.4, 69.6, 21.8; HRMS (ESI): calc. for [(C10Hl lNO4)H] (M+H) 210.0766, found 210.0761. Example 53:

Preparation of Allyl-4-nitrobenzoate:

Yield: 82%; 1.12 g; colorless liquid; IR (CHC13, cm-1): umax 3115, 2980, 1720, 1620, 1580, 1470, 1320, 1153; IH NMR (200 MHz, CDC13): δ 8.17-8.34 (m, 4H), 5.93-6.14 (m, IH), 5.28-5.50 (m, 2H), 4.86 (d, J = 5.8 Hz, 2H); 13C NMR (50 MHz, CDC13): δ 164.1, 150.6, 135.5, 131.6, 130.7, 123.5, 119.0, 66.3; HRMS (ESI): calc. for [(C10H9NO4)H] (M+H) 208.0610, found 208.0615.

Example 54:

Preparation of Prop-2-yn-l-yl 4-nitrobenzoate:

Yield: 80%; 1.08 g; colorless liquid; IR (CHC13, cm-1): vmax 2990, 2975, 1716,

1620, 1580, 1410, 1260, 1150, 949, 748; IH NMR (200 MHz, CDC13): δ 8.19-8.36 (m, 4H), 4.97 (d, J = 2.5 Hz, 2H), 2.54 (t, J = 2.5 Hz, IH); 13C NMR (50 MHz, CDC13): δ 163.8, 150.8, 134.7, 130.9, 123.6, 75.8, 53.2; HRMS (ESI): calc. for [(C10H7NO4)H] (M+H) 206.0453, found 206.0459.

Example 55:

Preparation of tert-butyl 3-nitrobenzoate:

Yield: 52%; 0.76 g; colorless oil; IR (CHC13, cm-1): umax 2996, 1725, 1610, 1520, 1490, 1260, 1152, 1050; IH NMR (200 MHz, CDC13): δ 1.65 (s, 9H), 7.51-7.74 (m, IH), 8.25-8.53 (m, 2H), 8.79 (s, IH); 13C NMR (50 MHz, CDC13): δ 163.2, 148.22, 135.0, 133.7, 129.2, 126.8, 124.3, 82.3, 28.1; HRMS (ESI): calc. for [(C11H13N04)H] (M+H) 224.0923, found 224.0929.

Example 55:

Preparation of (IR, 2S, 4R)-l,7,7-trimethylbicyclo[2.2.1]heptan-2-yl benzoate :

Yield: 80%; 1.60 g; pale yellow gum; [a]D25 -44.8 (c 2.5, CHC13) {lit.lOa [a]D30 - 45 (c 1.0, CHC13); IR (CHC13, cm-1): umax 2980, 1720, 1630, 1528, 1470, 1125, 1080, 945; IH NMR (200 MHz, CDC13): δ 7.92-8.13 (m, 2H) , 7.36-7.61 (m, 3H), 5.01-5.19 (m, IH), 2.32-2.62 (m, IH), 1.98-2.23 (m, IH), 1.65-1.96 (m, 3H), 1.05-1.59 (m, 5H), 0.92 (s, 6H); 13C NMR (50 MHz, CDC13): δ 166.6, 132.7, 130.9, 129.5, 128.3, 80.4, 49.1, 47.9, 45.0, 37.0, 28.2, 27.4, 19.8, 19.0, 13.7; HRMS (ESI): calc. for [(C17H2202)H] (M+H) 259.1698, found 259.1690. Example 56:

Preparation of (IS, 2R, 5S)-2-isopropyl-5-methylcyclohexyl 3-nitrobenzoate:

Yield: 81%; 1.63 g; colorless gum; [a]D25 -83.5 (c 2, CHC13) {lit.10b [a]D25 -83.7 (c 1.5, CHC13); IR (CHC13, cm-1): vjmax 3110, 2950, 1725, 1580, 1425, 1350, 1230, 1050, 948; 1H NMR (200 MHz, CDC13): δ 8.84 (s, 1H), 8.32-8.47 (m, 3H), 7.65 (t, J = 8.0 Hz, 1H), 4.99 (td, J = 10.8, 4.5 Hz, 1H), 1.86-2.21 (m, 1H), 1.69-1.86 (m, 2H), 1.53-1.67 (m, 2H), 1.22- 1.34 (m, 1H), 1.01- 1.20 (m, 3H), 0.94 (dd, J = 6.7, 3.4 Hz, 8H), 0.80 (d, J = 7.0 Hz, 3H); 13C NMR (50 MHz, CDC13): δ 163.9, 148.4, 135.3, 132.6, 129.5, 127.2, 124.6, 76.1, 47.2, 40.9, 34.3, 31.5, 26.6, 23.6, 22.1, 20.8, 16.5; HRMS (ESI): calc. for [(C17H23N04)H] (M+H) 306.1705, found 306.1710.

Example 57:

Preparation of 2,2,6,6-tetramethylpiperidin-l-yl-3-nitrobenzoate:

To a stirred solution of 4-nitrobenzaldehyde (0.5 g, 3.3 mmol), 2,2,6,6- Tetramethylpiperidinyloxy (TEMPO) (0.51 g, 3.3 mmol) and Titanium superoxide (0.1 g, 10 wt%) in dry CH3CN (10 niL), TBHP (5-6 M solution in decane) (1.2 mL, 6.6 mmol) was added dropwise via a syringe and kept stirring at 25 oC for 6 h. After the reaction (checked by TLC), the reaction mixture was filtered through sintered funnel using CH2C12 as eluent. Then the organic layer was extracted with CH2C12, dried over anhydrous Na2S04, and evaporated under reduced pressure. The crude product was purified by column chromatography over silica (230-400 mesh) using petroleum ether/ ethyl acetate (4: 1 v/v) as eluent to give 6. Yield: 72%; 1.45 g; colorless gum; IR (CHC13, cm-1): vmax 2985, 1725, 1620, 1590, 1435, 1 156, 1085, 835; 1H NMR (200 MHz, CDC13): δ 8.29 (m, 1H), 8.09 (m, 1H), 7.40-7.65 (m, 2H), 1.70-1.87 (m, 3H), 1.62 (m, 2H), 1.41-1.53 (m, 1H), 1.29 (s, 6H), 1.13 (s, 6H); 13C NMR (50 MHz, CDC13): δ 166.3, 132.8, 130.6, 129.5, 128.4, 123.6, 60.4, 39.0, 31.9, 20.8, 17.0; HRMS (ESI): calc. for [(C16H22N204)H] (M+H) 307.1652, found 307.1648.

Example 58:

Preparation of (((2,2,6,6-tetramethylcyclohexyl)oxy)methyl)benzene To a well- stirred solution of 2,2,6,6-Tetramethylpiperidinyloxy (TEMPO) (1 g, 6.41 mmol) in dry toluene (10 mL), Ti superoxide (0.1 g, 10 wt%) and TBHP (5-6 M in decane) (2.3 mL, 12.82 mmol) were added in a dropwise manner and heated at 80 °C for 2 h. After that, the reaction mixture was filtered through sintered funnel using CH2C12 as eluent. Then the organic layer was extracted with CH2C12, dried over anhydrous Na 2 S0 4 , and evaporated in vacuu. The crude product was purified by column chromatography over silica (230-400 mesh) using petroleum ether/ ethyl acetate (19: 1 v/v) as eluent to give 7. Yield: 75%; 2.03 g; colorless liquid; IR (CHC13, cm-1): umax 3011, 2980, 2851, 1621, 1590, 1365, 1150, 890, 748; 1H NMR (200 MHz, CDC13): δ 7.29-7.43 (m, 5H), 4.84 (s, 2H), 1.43-1.65 (m, 6H), 1.27 (s, 6H), 1.16 (s, 6H); 13C NMR (50 MHz, CDC13): δ 138.3, 128.2, 127.4, 127.3, 78.7, 60.0, 39.7, 33.1, 20.3, 17.1; HRMS (ESI): calc. for [(C16H250)H] (M+H) 248.2009, found 248.2020.

Example 59:

Preparation of 3-butylphthalide:

To a stirred solution of ortho-tolualdehyde 8a (1 g, 8.32 mmol) in CH2C12 (25 mL), ethylene glycol (0.516 g, 8.32 mmol) and PTSA (0.316 g, 1.66 mmol) were added and kept stirring at 25 oC for 3 h. After the reaction was over (judged by TLC), the organic layer was extracted with CH2C12, washed with aqueous saturated NaHC03 solution, dried over dried over anhydrous Na2S04, and evaporated under reduced pressure. The crude product was purified by column chromatography over silica (230-400 mesh) using petroleum ether/ ethyl acetate (9: 1 v/v) as eluent to furnish 2-(o-tolyl)-l,3-dioxolane 8a' in 90% yield.

Then to a stirred solution of 8a' (1 g, 6.09 mmol) in dry THF (30 mL), nBuLi in hexane (1.6 M) (4.5 mL, 7.3 mmol) was added via syringe in a dropwise manner at 0 oC and kept stirring for 30 min at same temperature. Then nBuI (1.12 g, 6.09 mmol) in dry THF (5 mL) was added to the reaction mixture at 0 oC slowly and left for stirring at 25 oC for 2 h. After the reaction was over (checked by TLC), it was quenched with 2N HC1 (10 mL) and kept stirring for another 1 h. Then the organic layer was extracted with ether, dried over dried over dried over anhydrous Na2S04, and evaporated under reduced pressure. After that, the crude product without further purification and characterization, was subjected to intramolecular oxidative esterification using TBHP in decane (5-6 M) (3.3 mL, 18.27 mmol) and Titanium superoxide (0.1 g, 10 wt%) and it was heated at 80 oC for 3 h. After the reaction was over (checked by TLC), it was filtered through sintered funnel using CH2C12 as eluent. Then the organic layer was extracted with CH2C12, dried over anhydrous Na2S04, and evaporated under reduced pressure. The crude product was purified by column chromatography over silica (230-400 mesh) using petroleum ether/ ethyl acetate (9: 1 v/v) as eluent to give 3-butylphthalide 8b in 70% yield.

Example 60:

Preparation of 2-(o-tolyl)-l,3-dioxolane:

Yield: 90%; 1.23 g; colorless liquid; IR (CHC13, cm- 1): rjmax 31 12, 2920, 1645, 1580, 1360, 1050, 845, 755; 1H NMR (200 MHz, CDC13): δ 7.46-7.60 (m, 1H), 7.15-7.29 (m, 3H), 5.97 (s, 1H), 4.10-4.20 (m, 2H), 3.98-4.09 (m, 2H), 2.42 (s, 3H); 13C NMR (50 MHz, CDC13): δ 136.5, 135.3, 133.5, 130.5, 128.8, 125.7, 125.6, 102.0, 65.1, 18.7; HRMS (ESI): calc. for [(C10H12O2)H] (M+H) 165.0916, found 165.0912.

Example 61:

Preparation of 3-butylphthalide:

Yield: 70%; 0.81 g; colorless liquid; IR (CHC13, cm- 1): rjmax 31 12, 2920, 1735, 1612, 1520, 1186, 1070; 1H NMR (200 MHz, CDC13): δ 7.88 (d, J = 7.5 Hz, 1H), 7.61 -7.74 (m, 1H), 7.40-7.58 (m, 2H), 5.47 (dd, I = 7.6, 4.1 Hz, 1H), 1.94-2.16 (m, 1H), 1.65-1.87 (m, 1H), 1.23- 1.58 (m, 4H), 0.81-0.99 (m, 3H); 13C NMR (50 MHz, CDC13): δ 170.1, 150.0, 133.7, 128.8, 126.113.8, 125.5, 121.6, 81.1, 34.4, 26.8, 22.3; HRMS (ESI): calc. for [(C 12H1402)H] (M+H) 191.1072, found 191.1076.

Example 62:

Mechanistic studies

To gain some insight into the mechanism of the reaction, the following experiments were performed (Scheme 2): (i) a competetive esterification experiment involving benzoic acid and 4-nitrobenzaldehyde with toluene under the reaction condition produced the corresponding 4-nitrobenzyl benzoate in 88% yield. This rules out the in situ formation of benzoic acid during the reaction course; (ii) addition of BHT (2,6-di-ier/-butyl-4- methylphenol) as a radical scavenger resulted in decrease of yield (trace amount) of ester products.

Ti superoxide C0 2 Bn

(10 wt%)

(ii)

0 2 N BHT, PhCH 3 Ο,Ν

1a TBHP (2 equiv) 2a, trace

°C of toluene or

f aldehyde)

TBHP, 80 °C 7, 75%

2 h

CQ 2 Me

0 ζΝ

3a, 80%

Scheme 2 Control experiments demonstrating radical pathway

(iii) Further, when TEMPO (1 equiv) was treated with la in the absence of either toluene or MeOH, under the reaction conditions, the corresponding TEMPO-ester adduct 6 was isolated in 72% yield. This result indicates the involvement of benzoyl radical in the catalytic cycle; (iv) it was further evidenced that reaction between toluene and TEMPO (1 equiv), under oxidative esterification, in the absence of aldehyde, producing benzyl oxyaminated product 7 in 75% yield; (v) in the absence of either toluene or methanol, la under the same protocol with excess Ti superoxide gave the solid intermediate II, which was characterized by FTIR spectrum (a strong carbonyl absorption frequency at 1742 cm "1 ) (Fig. 1); compound II on further reaction with MeOH gave the methyl ester 3a in 80% yield; this study confirms the formation of species C in the catalytic cycle; (vi) when ethyl benzene was subjected to oxidation with TBHP (1 equiv) and Ti superoxide (10 wt%) in the absence of aldehyde gave 1-phenylethan-l-ol (60% yield); (vii) when the aforementioned reaction was carried out in presence of light without catalyst, no reaction took place. This rules out the role of light in the reaction. Based on above observation, a possible catalytic cycle is proposed in Scheme 4. Thermal decomposition of TBHP in presence of aldehyde generates acyl radical B, which subsequently couples with titanium superoxide radical ion to form a Ti peroxo species C. Nucleopholic attack of alcohol onto C produces ester with the liberation of hydroxyl species D. Finally, 1 mole of TBHP is utilized to oxidize D to regenerate catalyst A ready for the next catalytic cycle.

Scheme 3 Catalytic cycle for oxidative esterification of aldehydi

The catalyst can be recovered readily by simple filtration and was reused successfully for 5 cycles in the oxidative esterification of la with methanol. The results are shown in Fig. 2, wherein, a slight decrease in catalytic efficiency could be observed after 4 th cycle. However, by the addition of TBHP (1 equiv) to the 4 th cycle reaction mixture, its activity can be restored to the original level (yield of ester: 80%). The catalyst was found to be quite active and not deteriorated as proven by reusability study, powder XRD of used catalyst and A AS analysis of reaction sample for Ti leaching.

Finally, its intramolecular version is demonstrated in the short synthesis of 3- butylphthalide, an anti-convulsant agent used in the treatment of stroke. Thus, o- pentylbenzaldehyde, readily obtained from o-tolualdehyde (8a), was subjected to intramolecular oxidative esterification under the present protocol to afford 8b in 70% yield (Scheme 4).

Scheme 4 Synthesis of anti-convulsant drug 3-butylphthalide

AC-200 spectrometer unless mentioned otherwise. Infrared spectra were recorded on Shimadzu FTIR-8400 spectrometer and absorption is expressed in cm "1 . ESI-MS were recorded on a Thermo Finnigan LCQ Advantage spectrometer in ESI mode with a spray voltage of 4.8 kV. All chemicals are purchased from Sigma-Aldrich and used without further purification. Purification was done using column chromatography (230-400 mesh). In 13 C NMR spectrum, C-peak at 96.1 corresponds to CC1 4 , as we have used (CDCI 3 : CCI 4 7:3) solvent for NMR study. Optical rotations were measured using sodium D line on a IASCO- 181 digital polarimeter.

ADVANTAGES OF THE PRESENT INVENTION: 1. Ti-superoxide is a heterogeneous catalyst and its synthesis is simple and well characterized.

2. Large range of substrate scope. 3. Reaction procedure is simple, efficient and single step.