BACKGROUND OF THE INVENTION Deoxygenation of cis vicinal diols into olefms, especially in natural products, nucleosides, antibiotics and carbohydrates, is a challenge. Efficient and mild methodologies, compatible with other sensitive functional groups and ring systems, are needed (see E. Block, Org. Reacts., 1984, 30, 457). A good summary of deoxygenation techniques for converting vicinal diols to unsaturated systems was published by Aldrich Chemical Co., J. Org. Chemi, December 1990. Included are the Corey-Winter and Eastwood methods, which generate a carbene intermediate, the Barton-McCombie method, which uses free radical fragmentation of bis-xanthates with tributyltin hydride or with certain silanes, and the Robins-Moffatt method which uses an α- acetoxyisobutyryl bromide reagent. The conversion of 1,2-dibromides into olefms with tellurium or sellurium compounds has been reported (see P. Prince et al., J. Org. Chem., 1966, 31, 4292; L. Engman, Tetrahedron Lett., 1982, 23, 3601, and T.K. Raja, Indian J. Chem., 1980, 19B, 812). However, the preparation of vicinal dibromides is generally not simple. Olefms are commonly protected as dibromides, thus necessitating debromination by the above techniques. Deoxygenation of nucleosides has recently received a great deal of attention. Acquired immunodeficiency (AIDS) is a consequence of infection by the human immunodeficiency virus (HIV). Several 2',3'-dideoxynucleosides have been shown to be effective in the treatment of cells infected with HIV. One compound, 3'-azido-3'-deoxythymidine (AZT), has been approved by the FDA in the United States for the treatment of individuals with AIDS. 2',3'- Dideoxyinosine (DDI) has recently received FDA approval for use in patients for whom AZT is no longer effective (Chem. and Eng. News, 1991, Oct. 14, p.17). These, and related nucleoside derivatives, are believed to inhibit viral reverse

transcriptase by competing with the natural substrates at the nucleotide binding site on the enzyme, .and the modified nucleosides are incorporated into proviral DNA, which then stops growing. Other nucleosides of interest in respect of their activity against HTV include the unsaturated nucleoside l-(2,3-dideoxy-β-D- glyceropent-2-enofuranosyl)thymine, (D4T) also known as 2',3'-dideoxy-2',3'- didehydro-5-methyluridine, 2',3'-dideoxyadenosine (DDA), and 2\3'- dideoxycytidine (DDC). D4T has been reported to have a comparable potency with AZT against HTV in culture. Various approaches for an efficient preparation of D4T and related compounds are under investigation (see Mansuri, M et. al., J.Org.Chem. 1989, 54, 4785). Cosford et al. (J. Org. Chem., 1991, 56, 2161), report the preparation of several thymidine derivatives with nucleophilic selenium reagents to produce, after selenoxide elimination, the desired unsaturation at the 2',3'-position in the sugar moiety of the nucleosides. In spite of considerable effort in this area there is still a need for a mild, efficient method for converting cis vicinal diols into olefins, particularly for the introduction of 2',3'-unsaturation in the sugar moiety of nucleosides.

SUMMARY OF THE INVENTION The inventor discovered that cis vicinal diols can be converted to olefins in very high yield, under mild conditions, using telluride or selenide reagents. In accordance with the process of this invention, a cis vicinal diol is reacted to convert the hydroxyl groups into good leaving groups for nucleophilic substitution. Leaving groups which replace the hydroxyl hydrogen but which leave the hydroxyl oxygen intact are used. Particularly preferred leaving groups are alkyl or aryl sulfonate groups such as mesylates and tosylates. The product is then reacted with a source of Te ^2" or Se ^2' , preferably an alkali metal telluride or selenide, to form the desired olefin. The process is particularly suited for generating 2',3'-unsaturation in the sugar moiety of nucleosides. It should be understood that the term cis vicinal diols is meant to include hydrocarbon substructures with hydroxyl groups on adjacent C-atoms, the

hydroxy groups being either in a cis relationship or being able to adopt a cis relationship during the reaction, as discussed more fully hereinafter. Without being bound by the same, it is believed that the reaction proceeds via the generation of an epitelluride or episelenide intermediate as shown in equation 1 (with the leaving groups being illustrated by mesylate groups (OMs):

Te ^2' z Te _N -» C = C + Te (1) C - C

OH OH OMs OMs

(See D. Clive et al., J. Org. Chem., 1980, 45, 2347, the epitellurides being generated by different techniques).

DESCRIPTION OF THE DRAWINGS Figure 1 is a formula sheet of representative dideoxy nucleosides.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Generally, any cis vicinal diol compound may be converted to an olefin by the process of this invention. For cyclic structures, cis vicinal idols are those diols having a pair of hydroxyl groups on adjacent carbons of the ring and that are on the s.ame side of the reference plane (adapted from "Naming and Indexing of Chemical Substances for Chemical Abstracts, A Reprint of Appendix IV to 1982 Index Guide", A. Chem. Soc, para 203. See also IUPAC Nomenclature of Organic Chemistry, Sections A,B,C,D,E,F and H, 1979, Pergamon Press, Oxford). Cis vicinal diol groups may be present in a wide range of hydrocarbons, including straight chain or branched alkanes and cycloalkanes. These hydrocarbon units may contain double and/or triple bonds and/or heteroatoms. Aryl and heteroaryl units may also be present. Any of these hydrocarbon, aryl or heteroaryl units may contain substituents and other functional groups such as ester, carbonyl or amide groups. Aliphatic bromide and iodide units should be avoided. Particularly important cis vicinal diols are natural

products, such as nucleosides, antibiotics and carbohydrates. If other reactive functional groups (ie. apart from the vicinal diol groups) such as nitrogen atoms (especially in the form of primary or secondary amines) or oxygen atoms (especially as alcohols or phenols) are present, in the diol, these can be N- or 0- protected, by procedures and protecting groups which are known in the art. For instance, nitrogen may be protected by conversion to aliphatic or aromatic amide groups or by benzylation. Oxygen may be protected by conversion to aliphatic or aromatic ester groups, or by silylation or benzylation. Exemplary protecting groups are (a) for nitrogen - acetamides, benzamides, (dimethylamino)methylene and silyl, and (b) for oxygen - acetates, benzoates, trityl (triphenylmethyl), dimethoxytrityl [bis (4-methoxylphenyl) phenylmethyl], and silyl. Other reactive functional groups can be protected, for example sulphur can be protected as esters and phenolic hydroxyl groups may be protected as methyl ethers or esters such as acetates. Numerous protecting groups for oxygen and nitrogen are given in Greene and Wuts (T.W. Greene .and P.G.M. Wuts, Protective Groups in Organic Synthesis, 2d Ed., Wiley, 1991). In accordance with the process of this invention, cis vicinal diols are first reacted to convert the adjacent hydroxyl groups into good leaving groups for nucleophilic substitution. Leaving groups which replace the hydroxyl hydrogen but leave the hydroxyl oxygen intact are used. Particularly preferred leaving groups are alkyl or aryl sulfonates. The alkyl group is typically a - C ₁₆ alkyl group which is branched, straight chain or cyclic and which may contain or carry non reactive substituents, for instance halides such as chloro, fluoro, alkoxy, aryloxy, alkyl esters, carboxamides [CONR',R" where R',R"=H, alkyl, aryl, heteroaryl], alkylthio, arylthio, aralkylthio, heteroarylthio, alkylamino, cycloalkylamino, aralkylamino, arylamino or heteroarylamino. The aryl group is typically a C ₆ - C _j6 -aryl group, which may contain and carry non reactive substituents such as those set out for alkyl sulfonates. Non reactive substituents include those substituents which will not undergo nucleophilic displacement by reaction with the telluride or selenide ions. Particularly preferred alkyl or aryl sulfonates are tosylates and mesylates. Other leaving groups include

trifluoromethane sulfonate (triflate), benzenesulfonate and, p- nitrobenzenesulfonate. Generation of a mesylate or tosylate leaving groups is accomplished by known techniques, see for example L. I. Fieser et al., Reagents for Organic Synthesis, Vol. 1, Wiley, New York, 1967, p. 662. In general, the diol is reacted with methanesulfonyl chloride or p-toluenesulfonyl chloride and an organic base such as triethylamine or pyridine, in an inert solvent, such as dichloromethane, ether, tetrahydrofuran, and chloroform. The reaction is preferably commenced at a low temperature (about 0°C) and the mixture is allowed to warm to room temperature. The converted diol is then reacted with a source of Te ^2" or Se ^2" to form the olefin. Preferably the telluride or selenide is provided as an alkali or alkaline earth metal salt (eg. Na, Li, K, Mg, and Ca). Sodium or lithium compounds are particularly preferred. Preparation of such compounds is by methods known in the art, (see "Tellurium", W. C. Cooper, Ed., Van Nostrand Reinhold, New York, 1971; "Selenium", R.A. Zingaro et al., Eds, Van Nostrand Reinhold, New York, 1974). The Li compounds are preferably generated in situ from metallic Te or Se .and lithium triethylborohydride (Super-Hydride, trade mark of Aldrich Chemical Co., Inc.) as described by D. Clive et al., J. Org. Chem., 1982, 47, 1641. The Na compounds are preferably prepared from sodium metal and elemental Te or Se in liquid ammonia (see G. Brauer, "Handbuch der Praparativen Anorganischen Chemie", E. Enke, Stuttgart, 1975, Vol. I, 431; A.B. Harvey et al., J. Chem. Phys. 1969, 50, 4949). The reaction . between the alkali metal telluride or selenide is performed under mild conditions (preferably room temperature) in a solvent in which the organic starting materials have some solubility. Ethereal solvents such as tetrahydrofuran (THF) and dioxane or acetonitrile are preferred, although alcoholic solvents such as ethanol may also be used. An inert atmosphere is preferred in order to avoid premature oxidation of the selenium or tellurium species. Once the desired olefin product is obtained, the protecting groups may be removed by well known techniques. For instance methods of removing

5'-0-trityl groups and N-acetyl groups are discussed in M.M. Mansuri et al., J. Org. Chem. 1989, 54,4785, N.D.P; Cosfard et al., J. Org. Chem., 1991, 56, 2161; B. Kaskar et al., J. Heterocyclic Chem., 1989, 26, 1531; and M. Sekine et al., J. Org. Chem., 1990, 55, 924. Hydrogenation of the olefin, particularly in respect of the nucleoside olefin products, also proceeds by well known techniques such as with hyrogen/Pd/charcoal. The process has been demonstrated with naturally occuring purine and pyrimidine nucleosides (O- and N- protected as appropriate). However, it should be understood that the process will also work for nucleosides in which the bases have been modified. Exemplary base-modified nucleic acids relevant to the treatment of AIDS are described in T. Yamaguchi et al., Nucleic Acids and Nucleotides, 1992, 11, 373 and P. Kumar et al., Nucleic Acids and Nucleotides, 1992, 11, 404. Thus the term "nucleoside", as used herein and in the claims is meant to include those with natural or modified bases. Exemplary saturated and unsaturated nucleosides relevant to AIDS treatment are shown in Figure 1. The invention is further illustrated by the following non-limiting examples.

Examples In the examples, compounds isolated by flash chromatography were homogeneous by TLC and, unless otherwise stated, were pure as judged by high field Η NMR spectra.

Example 1 (a) Preparation of Sodium Telluride (Na ₂ Te) A three-necked round-bottomed flask was charged with tellurium powder (200 mesh, 2.2053 g, 17.28 mmol) and a stirring bar. Sodium (0.7947 g, 34.57 mmol) was placed in a side-arm addition tube, and the central neck of the flask was fitted with a condenser charged with dry-ice/acetone and closed by a septum carrying both an entry needle for argon and an exit needle leading to an

oil bubbler. The third neck of the flask was temporarily closed by a septum and the flask was flushed with argon. The septum in the third neck was removed and immediately replaced by an adaptor (fitted with a tap) connected to a tank of liquid ammonia. The flask was now cooled with dry-ice/acetonitrile and ammonia was led in until ca. 200 mL had collected. The ammonia inlet was closed and a slow purge of argon was maintained. The stirrer was started and the sodium was added portionwise by tapping the side-arm addition tube. The mixture changed from red to bluish-green to white, by which stage formation of sodium telluride was complete. The cooling bath was removed from beneath the flask, and stirring was continued overnight, during which period the coolant in the condenser attained room temperature and the ammonia evaporated. The resulting beige sodium telluride (ca. 100% yield) was transferred in an argon-filled glove bag to a storage flask. (Cf. G. Brauer, Ed. "Handbuck der Praparativen Anorganischen Chemie", Ferdinand Enke: Stuttgart, 1975; Vol. I, p.431; A.B. Harvey et al., J. Chem. Phys. 1969, 50 4949).

(b) Preparation of Sodium Selenide (Na ₂ Se) A three-necked round-bottomed flask was charged with selenium powder (325 mesh, 2.8476 g, 36.0657 mmol) and a stirring bar. Sodium (1.7412 g, 75.7380 mmol) was placed in a side-arm addition tube, and the central neck of the flask was fitted with a condenser charged with dry-ice/acetone and closed by a septum carrying both .an entry needle for argon and an exit needle leading to an oil bubbler. The third neck of the flask was temporarily closed by a septum and the flask was flushed with argon. The septum in the third neck was removed and immediately replaced by an adaptor (fitted with a tap) connected to a flask containing a small amount (ca. 1 g) of sodium (to remove the water). This latter flask was in turn connected to a tank of liquid ammonia and was then cooled with dry-ice/acetonitrile. Ammonia was led in until ca. 200 mL had collected. The cooling bath was removed and the ammonia was transferred to the reaction vessel which was cooled with dry-ice/acetonitrile. The ammonia inlet was closed and a slow stream of argon was maintained. The stirrer was started and the sodium was added portionwise by tapping the side-arm addition tube. The mixture

changed color and eventually became white, by which stage formation of sodium selenide was complete. The cooling bath was removed and stirring was continued overnight, during which period the coolant in the condenser attained room temperature and the ammonia evaporated. The resulting slightly orange sodium selenide (ca. 100% yield) was transferred in an argon-filled golve bag to a storage flask.

Example 2 - Preparation of l-(3-butenyl)napthalene (a) 4-(l-naphthyl)-l 2-butanediol

Osmium tetroxide (1.7 mL, 2.5 % w/w solution of OsO ₄ in t-BuOH) was added to a stirred solution of l-(3-butenyl)-naphthalene (See J.B. Lambert et al., J. Org. Chem., 1979, 44, 1480) (1.1215 g, 6.1533 mmol) and 4- methylmorpholine-N-oxide (1.0331 g, 7.6526 mmol) in acetone (30 mL) and water (15 mL). Stirring at room temperature was continued for 43 h. EtOAc (100 mL) was then added and the organic layer was washed with water (1 x 100 mL) and 10% aqueous Na^O _j (2 x 50 mL). The organic extract was dried (MgSO ₄ ) and evaporated. Flash chromatrography of the residue over silica gel (5 x 20 cm), using 70% EtOAc in hexane, gave the diol (1.2004 g, 90%): FITR (CH ₂ C1 ₂ cast) 3360 cm ^"1 ; Η NMR (CDC1 ₃ , 200 MHZ) 6 1.70-2.05 (m, 4 H), 3.05- 3.45 (m, 2 H), 3.50 (dd, J= 7, 11 Hz, 1 H), 3.71 (dd, J = 3, 11 Hz, 1 H), 3.75- 3.95 (m, 1 H), 7.30-7.60 (m, 4 H), 7.60-7.80 (m, 1 H), 7.80-8.20 (m, 1 H); ¹³ C NMR (CDC1 ₃ , 75.469 MHz) 628.93, 34.02, 66.86, 71.89, 123.74, 125.55, 125.58, 125.92, 126.07, 126.82, 128.85, 131.81, 133.97, 137.89; exact mass, m/z calcd for C ₁₄ H ₁₆ O ₂ 216.1151, found 216.1151.

(b) 4-(l-Naphthyl)butane-l,2-diol dimethanesulfonate

Methanesulfonyl chloride (1.60 mL, 20.77 mmol) in CH ₂ C1 ₂ (10 mL) was added dropwise to a stirred and cooled (0°C) solution of 4-(l-naphthyl)- 1,2-butanediol (1.1229 g, 5.192 mmol) and pyridine (3.4 mL, 41.54 mmol) in CH ₂ C1 ₂ (10 mL) (argon atmoshpere). The ice bath was removed and stirring was continued for 16 h. The mixture was poured onto ice (ca. 50 g) and extracted with EtOAc (1 x 100 mL). The organic extract was washed with 10% aqueous CuSO ₄ (2 x 50 mL), dried (MgSO ₄ ) and evaporated. Flash chromatography of the residue over silica gel (3 x 30 cm), using 50:50 EtOAc-hexane, gave the dimesylate (1.8493 g, 96%): FITR (CH ₂ C1 ₂ cast) 1356, 1173 cm ^"1 ; *H NMR (CDC1 ₃ , 200 MHz) δ 2.05-2.40 (m,2 H), 3.0-3.10 (s, 3 H), 3.10-3.15 (s, 3 H), 3.15-3.45 (m, 2 H), 4.30 (dd, J = 6, 11 Hz, 1 H), 4.44 (dd, J = 3, 11 Hz, 1 H), 4.95-5.10 (m, 1 H), 7.30-7.65 (m, 4 H), 7.70-7.80 (m, 1 H), 7.93-8.05 (m, 1 H); ¹³ C NMR (CDCI ₃ , 75.469 MHz) 5 28.25, 32.08, 37.74, 38.90, 69.46, 78.66, 123.26, 125.63, 125.76, 126.30, 127.40, 129.01, 131.49, 134.00, 135.99; exact mass m/z calcd for C ₁₆ H ₂₀ O ₂ S ₂ 372.0702, found 372.0694.

(c) l-(3-Butenyl)naphthalene from dimesylate

Tellurium powder (200 mesh, .1674 g, 1.311 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 3.4 mL, 3.4 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). 4-(l- Naρhthyl)butane-l,2-diol dimethanesulfonate (488.3 mg, 1.311 mmol) in THF (5 mL) was then injected dropwise and the mixture was stirred for 20 h. The mixture was washed out of the flask with acetone and evaporated at room temperature. Flash chromatography of the residue over silica gel (2 x 30 cm) with hexane gave the pure (TLC, silica, hexane) olefin (.2105 g, 88.1%). (Cf. J.B.Lambert et al.)

Example 3 - Preparation of Oleic Acid Benzyl Ester (a) Benzyl (±)-(9S*,10R*)-9,10-dihydroxyoctadecanoate

HO OH

_ MXO ), <CH _j > _O _j Bn

Osmium tetroxide (3.95 mL, 2.5% w/w solution of OsO ₄ in t- BuOH) was added to a solution of oleic acid benzyl ester (see H.A. Shonle et al., J. Am. Chem. Soc. 1921, 43, 361) (5.6586 g, 15.1872 mmol) and 4- methylmorpholine-N-oxide (3.749 g, 27.77 mmol) in acetone (500 mL) and water (38 mL). The mixture was stirred at room temperature for 24 h, and then evaporated at room temperature to ca. 100 mL. EtOAc (200 mL) was added, the organic layer was washed with water (1 x 200 mL) and 10% aqueous Νa ₂ SO ₃ (3 x 200 mL), dried (MgSO ₄ ) and evaporated. Flash chromatrography of the residue over silica gel (10 x 50 cm), using 3.2% MeOH in CHC1 ₃ , gave the diol (4.4327 g, 72%): FTIR (CHC1 ₃ , cast) 3280, 1735 cm ^"1 ; Η NMR (CDC1 ₃ , 400 MHz) δ 0.80-1.00 (m, 3 H), 1.20-1.58 (m, 24 H), 1.58-1.75 (m, 2 H), 1.95 (broad s, 2 H), 2.35 (t, J = 7.2, 2 H), 3.50-3.70 (m, 2 H), 5.11 (s, 2 H), 7.28-7.45 (m, 5 H); ¹³ C

NMR (CDC1 ₃ , 75.469 MHz) δ 14.13, 22.70, 24.93, 25.95, 26.06, 29.06, 29.18, 29.31, 29.46, 29.59, 29.73, 31.21, 31.91, 34.34, 66.12, 74.69, 74.76, 128.20, 128.58, 173.70; exact mass m/z calcd for C ₂₅ H ₄₂ O ₄ 406.6015, C^H^O^H 370.2873, found 370.2869. Chemical ionization mass m/z calcd for [^ ₂ ^420., + NH ₄ ] ⁺ 424, found 424.

(b) Benzyl (±)-(9S*,10R*)-9,10-dihydroxyoctadecanoate dimethanesulfonate

Methanesulfonyl chloride (1.8 mL, 23.02 mmol) in CHC1 ₃ (4 mL), was added dropwise to a stirred and cooled (0°C) solution of benzyl (±)- (9S*,10R*)-9,10-dihydroxyoctadecanoate (1.1700 g, 2.878 mmol) and pyridine (3.80 ml, 46.04 mmol) in CHC1 ₃ (11 mL) (argon atmosphere). The ice bath was removed and stirring was continued for 40 h. The mixture was poured onto ice (ca. 50 g) and extracted with CHC1 ₃ (200 mL). The organic extract was washed with 10% aqueous CuSO ₄ (2 x 100 mL) and aqueous NaOH (.5 M, 1 x 50 mL), dried (MgSO ₄ ) and evaporated. Flash chromatography of the residue over silica gel (3 x 30 cm), using 5% MeOH in CHC1 ₃ , gave the dimesylate (1.5326 g, 95%), which contained a trace of impurity (signals at δ 3.0 and 3.1) but was suitable for the next stage: FOR (CHC1 ₃ , cast) 1734.720, 1357.482, 1175.355 cm ^"1 ; 'H NMR (CDC1 ₃ , 200 MHz) δ 0.78-0.98 (m,3 H), 1.18-1.88 (m, 26 H), 2.35 (t, J = 7 Hz, 2 H), 3.09 (s, 6 H), 4.68-4.88 (m, 2 H), 5.10 (s, 2 H), 7.25-7.38 (m, 5 H); ¹³ C NMR (CDC1 ₃ , 75.469 MHz) δ 14.07, 22.50, 22.61, 24.81, 25.36, 25.45, 28.91, 29.14, 29.27, 29.58, 29.65, 31.77, 34.22, 38.82, 66.06, 82.81, 82.91, 128.15, 128.54, 136.14, 173.52; exact mass m/z calcd for C ₂₇ H ₄₆ O _g S ₂ 562.2636, C ₂₇ H ₄₆ O _g S ₂ +lH ⁺ 563.2714, found 563.2732.

(c) Oleic acid benzyl ester from dimesylate. Use of Te—

Tellurium powder (200 mesh, 52.8 mg, 0.412 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 0.78 mL, 0.78 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). The dimesylate (108.3 mg, 0.1924 mmol) in dioxane (5 mL) was then injected dropwise and the mixture w.as stirred for 14 h. Starting material (TLC, silica, 40:60 CH ₂ C1 ₂ - hexane) was still present and so the mixture was heated at 100°C for 2 h (TLC control). The mixture was cooled, washed out of the flask with hexane, and evaporated at room temperature. Flash chromatography of the residue over silica gel (1.5 x 20 cm), using 40:60 CH ₂ Cl ₂ -hexane, gave the olefin (59.2 mg, 83%). (Cf. H.A. Shonle et al.).

(d) Oleic acid benzyl ester from dimesylate. Use of Se"

Selenium powder (325 mesh, 28.6 mg, 0.3593 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux

condenser. The flask was closed with a septum and flushed with .argon. Super- Hydride (1 M in THF, 0.68 mL, 0.68 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 20 min). The dimesylate (101.1 g, 0.1796 mmol) in dioxane (5 mL) was then injected dropwise and the mixture was stirred for 24 h. Starting material was still present (TLC, silica gel, 40:60 CH ₂ Cl ₂ -hexane), and the mixture was therefore heated at 100°C for 4 h. The mixture was cooled, washed out of the flask with hex.ane, and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 30 cm), using 35:65 CH ₂ Cl ₂ -hexane, gave the olefin (50.8 mg, 76%).

Example 4 - Preparation of 5-0-Benzyl-23-dideoxy-β-D-pent-2-enefuranoside (a) Methyl 5-0-benzyl-2 -Di-0-mesyl-β-D-ribofuranoside

Methanesulfonyl chloride (1.58 mL, 20.49 mmol) in CH ₂ C1 ₂ (10 mL), ws added dropwise to a stirred and cooled (0°C) solution of methyl 5-0- benzyl-β-D-ribofuranoside (See M. Kawana et al, Bull. Chem. Soc. Jpn., 1981, 54, 1492) (1.3025 g, 5.1223 mmol) and pyridine (3.31 mL, 40.98 mmol) in CH ₂ C1 ₂ (10 mL) (argon atmosphere). The ice-bath was removed and stirring was continued for 24 h. The mixture was poured onto ice (ca. 50 g) and extracted with EtOAc (100 mL). The organic extract was washed with 10% aqueous CuSO ₄ (2 x 50 mL), dried (MgSO ₄ ), and evaporated. Flash chromatography of the residue over silica gel (3 x 30 cm), using 30:70 EtOAc-hexane, gave the dimesylate (1.9635 g, 93%): FTIR (CH ₂ C1 ₂ , cast) 1384, 1180 cm ^"1 ; Η NMR (CDC1 ₃ , 300 MHz) δ 2.97 (s, 3 H), 3.15 (s, 3 H), 3.14 (s, 3 H), 3.62 (dd, J = 5.0, 10.5 Hz, 1 H), 3.70 (dd, J = 4.4, 10.5 Hz, 1 H), 4.40 (ddd, J = 4.5, 5.0, 6.5 Hz, 1 H) 4.58 (q, J = 12.0, 17.0 Hz, 2 H), 4.98 (dd, J = 1.5, 5.0 Hz, 1 H) 5.08 (d, J

= 1.5 Hz, 1 H), 5.20 (dd, J = 5.0, 6.5 Hz, 1 H), 7.28-7.45 (m, 5 H); ^,3 C NMR (CDC1 ₃ , 75.469 MHz) δ 38.12, 38.50, 55.65, 69.79, 73.74, 77.26, 79.15, 79.79, 105.68, 127.91, 128.02, 128.54, 137,49; exact mass m/z calcd for Cι ₅ H ₂₂ O ₉ S ₂ 410.0706, found 410.0734.

(b) Methyl 5-0-benzyl-2,3-dideoxy-β-D ^« pent-2-enofuranoside

B BnπOO-— i , o-, O ?Me

Tellurium powder (200 mesh, 72.1 mg, 0.565 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 1.27 ml, 1.27 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). Methyl 5-0-benzyl- 2,3-di-0-mesyl-β-D-ribofuranoside (100.3 mg, 0.244 mmol) in dioxane (5 mL) was then injected dropwise and the mixture was refluxed for 20 h. At this stage all of the dimesylate had reacted (TLC, silica, 30:70 ethyl acetate-hexane). The mixture was cooled, washed out of the flask with acetone, and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 20 cm), using 10% EtOAc in hexane, gave the olefin (37.3 mg, 69%). (Cf. M. Taniguchi et al., Tetrahedron 1974, 30, 3547 and K. Koga et al., Tetrahedron Lett. 1971, 263).

Example 5 - Preparation of 2',3'-Didehydro-2',3'-dideoxy-5'-0- (triphenylmethyl)uridine (a) 5'-0-(Triphenylmethyl)uridine

Uridine (155 mg, 0.6347 mmol), trityl chloride (199.4 mg, 0.7153 mmol), and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Pyridine (1.90 mL) was injected and the mixture was stirred at room temperature for 48 hi The mixture was then heated for 0.5 h at 100°C (oil bath temperature), cooled, and poured onto ice (ca.25 g). The gummy product was filtered off, washed with water, and dissolved in acetone. Evaporation of the solvent and flash chromatography of the residue over silica gel (2 x 30 cm), using 5% MeOH in CH ₂ C1 ₂ gave the pure (TLC) product (250.7 mg, 81%). (Cf. J.F. Codington et al., J. Org. Chem. 1964, 29, 558 and W.W. Zorbach et al. Ed. "Synthetic Procedures in Nucleic Acid Chemistry"; Wiley 1968, Vol I, p. 441).

(b) 5'-0-(Triphenylmethyl)uridine 2' '-dimethanesulfonate

Methanesulfonyl chloride ( 1.45 mL, 18.76 mmol) in CH ₂ C1 ₂ (8 mL) was added dropwise to a stirred and cooled (0°C) solution of S'-O- (triphenylmethyl)uridine (2.2816 g, 4.69 mmol) and pyridine (3.03 mL, 37.5 mmol) in CH ₂ C1 ₂ (10 mL) (argon atmoshphere). The ice-bath was removed and stirring was continued for 48 h. The mixture was poured onto ice (ca. lOOg) and extracted with EtOAc (2 x 100 mL). The organic extract was washed with water (2 x 100 mL), aqueous NaOH (.5 M, 1 x 50 mL), and 10% aqueous CuSO ₄ (1 x 100 mL, dried (MgSO ₄ ) and evaporated. Flash chromatography of the residue over silica gel (4 x 30 cm), using 3% MeOH in CH ₂ C1 ₂ , gave the pure ['H NMR (200 MHz)] dimesylate (2.6032 g, 86%): FTIR (CH ₂ C1 ₂ , cast) 1694, 1364, 1179 cm ^'1 ; Η NMR (CDC1 ₃ , 200 MHz) δ 3.10 (s, 3 H), 3.21 (s, 3 H), 3.50-3.75 (m, 2 H), 4.25-4.50 (m, 1 H), 5.25-5.65 (m, 3 H) 6.02 (d, J = 3 Hz, 1 H), 7.10-7.60 (m, 15 H), 7.72 (d, J = 8 Hz, 1 H), 9.32 (broad s, 1 H); ¹³ C NMR (CDC1 ₃ , 100 MHz) δ 38.62, 38.86, 60.87, 73.58, 78.24, 80.93, 88.18, 88.43, 103.20, 127.69, 128.24, 128.73, 139.95, 142.68, 150.49, 163.02; FABMS m/z calcd for [C ₃₀ H ₃₀ N ₂ O ₁₀ S ₂ + H] ⁺ 643.1412, found 643.1401.

(c) 2'3'-Didehydro-2' '-dideoxy-5'-0-(triphenylmethyl)uridine

Tellurium powder (200 mesh, 40.0 mg, 0.3135 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 0.66 mL, 0.66 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). The dimesylate (100

mg, 0.1556 mmol) in dioxane (5 mL) was then injected dropwise and the mixture was stirred for 48 h. The mixture was washed out of the flask with CH ₂ C1 ₂ , and evaporated at room temperature. Flash chromatography of the residue over silica gel (2 x 25 cm), using 50:35:15 CH ₂ Cl ₂ -toluene-MeCN, gave the olefin (55.9 mg, 80%). (Cf. M.M. Masuri et al., J. Organ. Chem. 1989, 54, 4780).

(d) 2' '-Didehydro-2' ^, -dideoxy-5 ^, -0-(triphenyhnethyl)-uridine (i) Use of sodium selenide

N^Se (0.0302 g, 0.2417 mmol) (prepared from the elements, as described above) and a small stirring bar were placed in a dry round-bottomed flask fused onto a condenser. The flask was closed with a septum and flushed with argon. The dimesylate (595 mg, 0.0967 mmol) in THF (2 mL) was then injected and the mixture was stirred for 48 h. The mixture was washed out of the flask with CH ₂ C1 ₂ and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 25 cm), using 55:25:20 CH ₂ Cl ₂ -toluene-MeCN, gave, after a second chromatography under the same conditions, the olefin (21.3 mg, 51%). (ii) Use of lithium selenide

Selenium powder (325 mesh, 14.8 mg, .1867 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with .argon. Super- Hydride (1 M in THF, 0.37 mL, 0.37 mmol) was injected and the mixture was stirred for ca. 4 h. A milky white suspension was formed after 10 min. The dimesylate (59.0 mg, 0.0934 mmol) in THF (3 mL), was then injected dropwise and the mixture was stirred for 20 h. The mixture turned brown on initial addition of the dimesylate solution. The mixture was washed out of the flask with CH ₂ C1 ₂ , and K ₂ CO ₃ was added. The mixture was then evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 20 cm), using 50:35:15 CH ₂ Cl ₂ -toluene-MeCN, gave the olefin (27.1 mg, 65%). (iii) Use of sodium telluride

Na ₂ Te (0.0940 g, 05415 mmol) (prepared from the elements, as described above) and a small stirring bar were placed in a dry round-bottomed flask fused onto a condenser. The flask was closed with a septum and flushed with argon. The dimesylate (139.2 mg, 0.2166 mmol) in THF (2 mL) was then injected and the mixture was stirred for 20 h at room temperature. The mixture was washed out of the flask with CH ₂ C1 ₂ , and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 25 cm), using 55:25:20 CH ₂ Cl ₂ -toluene-MeCN, gave the olefin (91.7 mg, 93%).

(iv) Use of lithium telluride in the presence of ethanol

Telluride powder (200 mesh, 41.7 mg, 0.3268 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 0.73 mL, 0.7313 mmol) was injected and the mixture stirred until a milky white suspension had formed (ca. 5 h). Ethanol (1 mL) was added. The dimesylate (100.0 mg, 0.1556 mmol) in ethanol (2 mL) was then injected dropwise and the mixture was stirred for 16 h. The reaction mixture was washed out of the flask with CH ₂ C1 ₂ and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 30 cm), using 55:25:20 CH ₂ Cl ₂ -toluene-MeCN, gave the olefin (26.5 mg, 38%).

(v) Use of lithium telluride in the presence of acetonitrile

Tellurium powder (200 mesh, 41.7 mg, 0.3268 mmol) and a small sitπing bar were placed in a dry round-bottomed flask fused onto a reflux

condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 0.73 mL, 0.7313 mmol) was injected and the mixture stirred until a milky white suspension had formed (ca. 5 h). The dimesylate (100.0 mg, 0.1556 mmol) in acetonitrile (2 mL) was then injected dropwise and the mixture was stirred for 16 h. The reaction mixture was washed out of the flask with CH ₂ C1 ₂ and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 30 cm), using 55:25:20 CH ₂ Cl ₂ -toluene-MeCN, gave the olefin (70 mg, 99%). Example 6 - Preparation of 2' '-Didehydro-2',3 ^, -dideoxy-5-methyl-5'-0- (triphenylmethyl)uridine (a) 5-Methyl-5'-0-(triphenylmethyl)uridine

Ribothymidine (194.4 mg, 0.7529 mmol), trityl chloride (233.9 mg, 0.8390 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Pyridine (2.2 mL) was injected and the mixture was stirred at room temperature for 24 h. The mxiture was poured onto ice (ca. 25 g) and the gummy product was filtered off, washed with water and dissolved in acetone. Evaporation of the solvent and flash chromatography of the residue over silica gel (2 x 25 cm), using 5% MeOH in CH ₂ C1 ₂ , gave the product (221.0 mg, 59%). (Cf. J.J. Fox et al., J. Am. Chem. Soc. 1957, 79, 2775).

(b) 5-Methyl-5'-0-(triphenylmethyl)uridine 2 ,3 -dimethan-sulfonate

Methanesulfonyl chloride (0.11 mL, 1.391 mmol) in CH ₂ C1 ₂ ( 1 mL) was added dropwise to a stirred and cooled (0°C) solution of 5-methyl-5'-O- (triphenylmethyl)uridine (174.1 mg, 0.3478 mmol) and pyridine (0.46 mL, 5.6 mmol) in CH ₂ C1 ₂ (3 mL) (argon atmosphere). The ice bath was removed and stirring was continued for 48 h. The mixture was poured onto ice (ca. 50 g) and extracted with EtOAc (2 x 50 mL). The organic extract was washed with water (2 x 50 mL), aqueous NaOH (.1 M, 1 x 50 mL), and 10% aqueous CuSO ₄ , dried (MgSO ₄ ), and evaporated. Flash chromatography of the residue over silica gel (2 x 30 cm), using 3% MeOH in CH ₂ C1 ₂ , gave the pure [Η NMR (200 MHz)] dimesylate (0.1898 g, 83%): FTIR (CH ₂ C1 ₂ , cast) 1693, 1364, 1180 cm ^"1 ; Η NMR (CDC1 ₃ , 400 MHz) δ 1.42 (s, 3 H), 3.08 (s, 3 H), 3.20 (s, 3 H), 3.48 (dd, J = 2.2, 11.2 Hz, 1 H), 3.64 (dd, J = 2.2, 11.2 Hz, 1 H), 4.30-4.45 (m, 1 H), 5.40- 5.55 (m, 2 H), 6.08 (d, J = 4.5 Hz, 1 H), 7.20-7.60 (m, 16 H), 9.69 (broad s, 1 H); ¹³ C NMR (CDC1 ₃ , 50.323 MHz) δ 11.75 38.68, 38,84, 61.92, 74.96, 77.24, 81.48, 87.83, 88.23, 112.38, 127.71, 128.22, 128.77, 135.31, 142.92, 150.64, 163.39; FABMS m/z calcd for [C ₃₁ H ₃₂ N ₂ O ₁₀ S ₂ + H]+ 657.1578, found 657.1548. (c) 2' '-Didehydro-2 ^, 3'-dideoxy-5-methyl.5'-0-(triphenyl. methyl)uridine

Tellurium powder (200 mesh, 24.9 mg, 0.1951 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 0.50 mL, 0.50 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). The dimesylate (60.1 mg, 0.0915 mmol) in THF (3 mL) was then injected dropwise and the mixture was stirred for 48 h. The mixture was washed out of the flask with CH ₂ C1 ₂ and evaporated at room temperature. Flash chromatography of the residue over silica gel (2 x 30 cm), using 50:35:15 CH ₂ Cl ₂ -toluene-MeCN, gave the pure [Η NMR (200 MHz)] olefin (38.6 mg, 90%). (Cf. N.D.P. Cosford et al., J. Org. Chem. 1991, 56, 2161).

Example 7 - Preparation of 2',3'-Didehydro-2',3'-dideoxy-5'-0- (triphenylmethyl)uridine (a) 5'-0-(Triphenyhnethyl)uridine 2'3'-di(p-toluenesulfonate)

p-Toluenesulfonyl chloride (470 mg, 1.466 mmol) in CH ₂ C1 ₂ (2 mL) was added dropwise to a stirred and cooled (0°C) solution of 5'-0- (triphenylmethyl)uridine (200 mg, 0.4111 mmol), pyridine (0.80 mL, 9.9 mmol) and 4-(dimethylamino)pyridine (5 mg) in CH ₂ C1 ₂ (2 mL) (argon atmosphere). The ice bath was removed, stirring was continued for 24 h and the mixture was then heated at 50°C for a further 24 h. The mixture was poured onto ice (ca. 25 g) and extracted with CH ₂ C1 ₂ (1 x 100 mL). The organic extract was washed with 10% aqueous CuSO ₄ (2 x 50 mL), dried (MgSO ₄ ) and evaporated. Flash chromatography of the residue over silica gel (1 x 30 cm), using 55:25:20 CH ₂ Cl ₂ -toluene-MeCN, gave the ditosylate (93.8 mg, 29%): 'H NMR (CDC1 ₃ ,

200 MHz) δ 2.40 (s, 3 H), 2.45 (s, 3 H), 3.30-3.50 (m, 2 H), 4.30-4.45 (m, 1 H), 5.00-5.35 (m, 3 H), 6.10 (d, J = 6 Hz, 1 H), 7.15-7.45 (m, 20 H), 7.64 (d, J = 8 Hz, 2 H), 7.77 (d, J = 8 Hz, 2 H), 7.96 (broad s, 1 H).

(b) Conversion of 5'-0-(Triphenylmethyl)uridine 2',3'-di(p-toluenesulfonate) into 2' '-Didehydro-2' 3'-dideoxy-5'-O-(triphenylmethyl)uridine

Tellurium powder (200 mesh, 11.7 mg, 0.0919 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with .argon. Super- Hydride (1 M in THF, 0.21 mL, 0.2101 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). The ditosylate (34.8 mg, 0.0438 mmol) in THF (1 mL) was then injected dropwise and the mixture was stirred for 24 h. The mixture was washed out of the flask with CH ₂ C1 ₂ , and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 30 cm), using 50:25:20 CH ₂ Cl ₂ -toluene-MeCN, gave the olefin (11.8 mg, 60%).

Example 8 - Preparation of N-Acetyl-2' '-didehydro-2',3'-dideoxy-5'-0- (triphenylmethyl)cytidine and N-Acetyl(-2',3'-dideoxy-5'-0- (triphenylmethyl)cytidine (a) N-AcetyI-5'-0-(triphenylmethyl)cytidine

N-Acetylcytidine (see D.M. Brown et al., J. Chem. Soc. 1956, 2384) (1.000 g, 3.5057 mmol), trityl chloride (1.0751 g, 3.8563 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Pyridine (10.2 mL) was injected and the mixture was stirred at room temperature for 36 h. The mixture was evaporated, diluted with CH ₂ C1 ₂ , and again evaporated. The gummy residue was washed with water and the residue was dissolved in acetone. The solution was dried (MgSO ₄ ) and evaporated. Rash chromatography of the residue over silica gel (4.5 x 30 cm), using 7% MeOH in CH ₂ C1 ₂ , gave the product (1.4752 g, 80%). (Cf. H.U. Blank et al., Justus Liebigs Ann. Chem. 1970, 742, 16). (b) N-Acetyl-5'-0-(triphenylmethyl)cytidine 2 ,3 -dimethane-sulfonate

Methanesulfonyl chloride (0.0609 mL, 0.7862 mmol) in CH ₂ C1 ₂ (0.6 mL) was added dropwise to a stirred and cooled (0°C) solution of N-acetyl- 5'-0-(triphenylmethyl)cytidine (0.1037 g, 0.1965 mmol) and triethylamine (0.0604 mL, 0.4339 mmol) in CH ₂ C1 ₂ (1 mL) (argon atmosphere). The mixture was stirred at 0°C for 25 min, poured onto ice (ca. 100 g), and extracted with CH ₂ C1 ₂ (100 mL). The organic extract was washed with water (1 x 100 mL), saturated aqueous ΝaHCO ₃ , (1 x 100 mL), and water (1 x 100 mL), dried (MgSO ₄ ) and evaporated. Flash chromatography of the residue over silica gel (1 x 30 cm), using 3.5% MeOH in CH ₂ C1 ₂ , gave the pure [Η NMR (200 MHz)] dimesylate (0.1086 g, 81%): FTIR (CH ₂ C1 ₂ , cast) 1722, 1666.049, 1490, 1366, 1181 cm ^"1 ; Η NMR (CD ₂ C1 ₂ , 200 MHz) δ 2.18 (s, 3 H), 3.06 (s, 3 H), 3.35 (s, 3 H), 3.56 (dd, J = 2.2, 11.5 Hz, 1 H), 3.68 (dd, J = 2.2, 11.5 Hz, 1 H), 4.30-4.50 (m, 1 H), 5.37-5.55 (m, 2 H), 5.97 (s, br, 1 H), 7.10 (d, J = 7 Hz, 1 H), 7.20-7.60 (m, 15 H), 8.25 (d, J = 7 Hz, 1 H), 8.90 (broad s, 1 H); ¹³ C NMR (CD ₂ C1 ₂ , 100.614 MHz) δ 25.01, 38.90, 39.24, 60.49, 72.58, 79.89, 80.58, 88.22, 90.44, 97.46, 127.87, 128.47, 128.65, 129.02, 143.12, 143.30, 144.85, 155.29, 163.71, 171.23; FABMS m/z calcd for [C ₃₂ H ₃₃ N ₃ O ₁₀ S ₂ + H] ⁺ 684.1687, found 684.1651. (c) N-Acetyl^'^'-didehydro^'^'-dideoxy-S'-O-ttriphenyl-methy^cyt idine (i) Use of lithium telluride

Tellurium powder (200 mesh, 39.2 mg, 0.3071 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 0.66 mL, 0.6581 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). The dimesylate

(100.0 mg, 0.1463 mmol) in THF (2 mL) was then injected dropwise .and the mixture was stirred for 14 h. The mixture was washed out of the flask with CH ₂ C1 ₂ , and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 15 cm), using 50:30:20 MeCN-CH ₂ Cl ₂ -toluene, gave the olefin (60.3 mg, 83%): Η NMR (CD ₂ C1 ₂ , 200 MHz) δ 2.18 (s, 3 H), 3.30- 3.50 (ms, 2 H), 4.95-5.15 (m, 1 H), 5.93-6.08 (m, 1 H), 6.18-6.43 (m 1 H), 6.87 (d, J = 7 Hz, 1 H), 6.92-7.05 (m, 1 H), 7.15-7.55 (m, 15 H), 8.0 (d, J = 7 Hz, 1 H), 8.92 (broad, s, 1 H).

(ii) Use of sodium telluride

Na ₂ Te (.0682 g, 0.3929 mmol) (prepared from the elements, as described above) and a small stirring bar were placed in a dry round-bottomed flask fused onto a condenser. The flask was closed with a septum and flushed with argon. The dimesylate (107.5 mg, 0.1572 mmol), in THF (2 mL) was then injected and the mixture was stirred for 24 h. The mixture was washed out of the flask with CH ₂ C1 ₂ , and evaporated at room temperature. Flash chromatography of the residue over silica gel (1 x 25 cm), using 50:30:20 MeCN-CH ₂ Cl ₂ -toluene, gave the olefin (33.0 mg, 42%).

(d) N-Acetyl-2' '"dideoxy-5'-0-(triphenylmethyl)cytidine by Hydrogenation of N-Acetyl.2' '-didehydro-2',3'-dideoxy-5'-0-(triphenylmethyl)cytidine

N-Acetyl-2',3'-didehydro-2',3'-dideoxy-5'-O- (triphenylmethyl)cytidine (0.498 g, 0.1009 mmol), EtOAc (3 mL) and MeOH (1 mL) were placed in a test tube along with Pd/charcoal (10%w/w, 10 mg). The test tube was supported with glass woold in a Parr vessel and shaken with hydrogen (50 psi) for 4 h. The mixture was filtered and evaporated. Flash chromatography of the residue over silica gel (1 cm x 30 cm), using 50:30:20 MeCΝ-CH ₂ Cl ₂ -toluene, gave the product (30.4 mg, 61%): Η NMR (CD ₂ C1 ₂ , 200 MHz) δ 1.82-2.03 (m, 1 H), 2.20 (s, 3 H), 2.35-2.63 (m, 1 H), 3.28-3.58 (m, 2 H), 4.17-4.38 (m, 1 H), 5.96-6.10 (m, 1 H), 7.12 (d, J = 7 Hz, 2 H), 7.20-7.60 (m, 15 H), 8.32 (d, J = 7 Hz, 2 H), 9.68 (broad s, 1 H).

Example 9 - Preparation of 5-0-Acetyl-2'-3'-didehydro-2' '-dideoxyuridine (a) Preparation of 5'-0-Acetyluridine 2' '-dimethanesulfonate (i) 2' '-0-Isopropylideneuridine

Uridine (1.000 g, 4.095 mmol), p-toluenesulfonic acid (101.3 mg, 0.5324 mmol), and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Dry acetone (15 mL) and 2,2-dimethoxypropane (3.22 mL) were injected into the flask and the mixture was stirred at room temperature for 15 h. Sodium methoxide was then added until the solution became slightly basic (moist litmus paper). The mixture was evaporated at room temperature and flash chromatography of the residue over silica gel (3 x 30 cm), using 5% MeOH in CH ₂ C1 ₂ , gave the isopropylidene derivative (1.0587 g, 91%). (Cf. H.P.M. Fromageot et al., Tetrahedron 1967, 22, 2315).

(ii) 5'-0-Acetyluridine

( 130.2 mg, 0.4580 mmol) and a small stirring bar were placed in a round-bottomed flask. The flask was sealed with a septum and flushed with argon. Pyridine (1 mL) and acetic anhydride (0.11 mL) were injected and the mixture was stirred at room temperature for 15 h. Methanol (0.37 mL) was added and the mxiture was stirred for 1 h. The solution was evaporated three times from a 1:1 mixture of EtOH and water. The product was dissolved in formic acid (60%, 1.44 mL), and the solution was stirred for 3 h and then evaporated. Flash chromatography of the residue over silica gel (2 x 30 cm), using 7% MeOH in CH ₂ C1 ₂ , gave the product. (Cf. H.P.M. Fromageot et al.).

(iii) 5'-0-Acetyluridine 2' '-dinιethanesulfonate

Methansulfonyl chloride (0.90 mL, 11.589 mmol), in CH ₂ C1 ₂ (1.6 mL), was added dropwise to a stilted and cooled (ice bath) solution of 5'-0- acetyluridine (0.3317 g, 1.159 mmol) and pyridine (1.50 mL, 18.542 mmol) in CH ₂ C1 ₂ (3 mL) (argon atmosphere). The ice bath was removed and stirring was continued for 24 h. The mixture was evaporated at room temperature, and flash chromatography of the residue over silica gel (3.5 x 30 cm), using 3% MeOH in CH ₂ C1 ₂ , gave, after a second chromatography under the same conditions, the pure [Η NMR (200 MHz)] dimesylate (0.4177 g, 81%). FTIR (MeOH, cast) 1365, 1180 cm ^"1 ; Η NMR (acetone-d ₆ , 200 MHz) δ 2.07 (s, 3 H), 3.26 (s, 3 H), 3.32 (s, 3 H), 4.30-4.60 (m, 3 H), 5.48 (t, J = 6 Hz, 1 H), 5.55-5.80 (m, 2 H), 6.0 (d, J = 3 Hz), 7.76 (d, J = 8 Hz, 1 H), 10.23 (broad s, 1 H); ¹³ C NMR (acetone-d ₆ , 50 MHz) 620.61, 38.66, 38.74, 62.58, 75.14, 78.61, 80.24, 91.11, 103.34, 141.93, 151.33, 163.36, 170.57; FABMS m/z calcd for [Cι ₃ H _I8 N ₂ O _n S ₂ + H] ⁺ 443.0431, found 443.0398.

(b) 5'-0-Acetyl-2' '-didehydro-2' '-dideoxyuridine

Tellurium powder (200 mesh, 60.6 mg, 0.4747 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 1.17 mL, 1.175 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). The dimesylate (100.0 mg, 0.2260 mmol) in THF (3 mL) ws then injected dropwise and the mixture was stirred for 96 h. The mixture was washed out of the flask with CH ₂ C1 ₂ and evaporated at room temperature. Hash chromatography of the residue over silica gel (1 x 30 cm), using 3% MeOH in CH ₂ C1 ₂ , gave the olefin (7.7 mg, 14%). (Cf. Y. Amino et al., Bull. Chem. Soc. 1991, 39, 622).

Example 10 - Preparation of 2\3'-Didehydro-2',3'-dideoxy-N- [ (dimethylamino)methylene] -5'-0- [bis(4-methoxyph enyl) - phenylmethyl]adenosine (a) N-[(Dimethylamino)methylene]-5'-0-[bis(4-methoxyphenyl)- phenylmethyl]adenosine 2',3 -dimethanesulfonate

Methanesulfonyl chloride (0.37 mL, 4.8073 mmol) in CH ₂ C1 ₂ (5 mL) was added dropwise to a stirred and cooled (0°C) solution of N- [(dimethylamino)methylene]-5'-0-[bis(4-methoxyphenyl)phenylm ethyl]adenosine (see R. Vinayak et al., Nucleic Acids Research, 1992, 20, 1265) (1.001 g, 1.6024 mmol) and triethylamine (1.34 mL, 9.6145 mmol) in CH ₂ C1 ₂ (8 mL) (argon atmoshphere). The mixture was stirred at 0°C for 30 min, poured onto ice (ca. 200 g), and extracted with CH ₂ C1 ₂ (2 x 150 mL). The organic extract was washed with water (1 x 100 mL), saturated aqueous NaHCO ₃ (1 x 100 mL), and

water (1 x 100 mL), dried (MgSO ₄ ) and evaporated. Flash chromatography of the residue over silica gel (3 x 30 cm), using 49:30:20: 1 CH ₂ Cl ₂ -toluene-MeCN-Et ₃ N, gave the pure ['H NMR (200 MHz)] dimesylate (1.0895 g, 87%: FITR (CH ₂ C1 ₂ , cast) 1365, 1180 cm ^"1 ; 'H NMR (acetone-d ₆ , 200 MHz) δ 3.10-3.30 (m, 12 H), 3.40 (dd, J = 4, 11 Hz, 1 H), 3.62 (dd, J = 3.5, 11 Hz, 1 H), 3.75 (s, 3 H), 3.76 (s, 3 H), 4.40-4.60 (m, 1 H), 5.85-6.00 (m, 1 H), 6.30-6.55 (m,2 H), 6.70-6.90 (m, 4 H), 7.10-7.38 (m, 7 H), 7.38-7.55 (m, 2 H), 8.30 (s, 1 H), 8.31 (s, 1 H), 8.85- 9.00 (s, br, 1 H); ¹³ C NMR (acetone-d ₆ , 50 MHz) δ 35.02, 38.74, 38.80, 41.13, 55.60, 62.99, 77.08, 77.47, 82.51, 87.67, 114.06, 127.68, 128,63, 129.14, 131.04, 136.53, 136.65, 145.76, 152.45, 153.25, 159.14, 159.82, 161.16; FABMS m/z calcd for [C _3β H ₄ oN ₆ 0,oS ₂ + H] ⁺ 781.2328, found, 781.2337.

(b) 2'3'-Didehydro-2' _; 3'-dideoxy-N.[(dimethylamino)methylene]-5'-0-[bis(4- methoxyphenyI)phenylmethyl]adenosine

Tellurium powder (200 mesh, 19.9 mg, 0.156 mmol) and a small stirring bar were placed in a dry round-bottomed flask fused onto a reflux condenser. The flask was closed with a septum and flushed with argon. Super- Hydride (1 M in THF, 0.33 mL, 0.33 mmol) was injected and the mixture was stirred until a milky white suspension had formed (ca. 5 h). The dimesylate (58 mg, 0.0742 mmol) in THF (2 mL) was then injected dropwise and the mixture was stirred for 16 h. The mixture was washed out of the flask with CH ₂ C1 ₂ , and evaporated at room temperature. Flash chromatography of the residue over silica

gel (1 x 30 cm), using 29:20:50:1 CH ₂ Cl ₂ -toluene-MeCN-Et ₃ N, gave the olefin (39.1 mg, ca.89%), containing [ ^J H NMR (200 MHz)] trace impurities. ^l H NMR (acetone-d ₆ , 200 MHz) δ 3.02-3.30 (m, 6 H), 3.30-3.46 (m, 1 H), 3.46-3.65 (m, 1 H), 3.74 (s, 3 H), 3.75 (s, 3 H), 5.02-5.18 (m, 1 H), 6.15-6.30 (m, 1 H), 6.48- 6.60 (m, 1 H), 6.60-6.90 (m, 4 H), 7.00-7.32 (m, 7 H), 7.32-7.50 (m, 2 H), 8.01 (s, 1 H), 8.42 (s, 1 H), 8.86-9.05 (s, 1 H). The terms and expressions used in this specification are used as terms of description and not of limitation. There is no intention, in using such terms and expressions, of excluding equivalents of the features shown and described, it being recognized that the scope of the invention is defined and limited only by the claims which follow. All publications referred to in the specification are incorporated herein by reference.