The present invention relates to a process (Mukaiyama Aldol reaction) for the preparation of compounds of formula I

wherein

R1 is Ci-4 alkyl, C3-6 cycloalkyl-C1-4 alkyl or aryl-C1-4 alkyl;

R2 is C1-4 alkyl, benzyl, substituted benzyl or allyl;

R3 is C1-4 alkyl or allyl;

R4 is C1-4 alkyl, allyl, benzyl or substituted benzyl;

R4 is benzyl or substituted benzyl; or

R1 and R4 together form a (CH2)3-group.

Mukaiyama Aldol reactions are known in the prior art. Dialkyl acetals are known to be substituted by Mukaiyama aldol reactions with silyl enol ethers or silyl ketene acetals affording β-alkoxy ketones or esters (K. Saigo, M. Osaki, T. Mukaiyama, Chem. Lett. 1976, 769-770; T. Mukaiyama, M. Murakami, Synthesis 1987, 1043-1054; S. Kano, T. Yokomatsu, H. Iwasawa, S. Shibuya, Chem. Lett. 1987, 1531-1534; M. A. Graham, A. H. Wadsworth, M. Thornten-Pett, B.Carrozzini, G. L. Cascarano, C. M. Rayner, Tetrahedron Lett. 2001, 42, 2865-2868; M. A. Graham, A. H. Wadsworth, M. Thornten- Pett, B.Carrozzini, G. L. Cascarano, C. M. Rayner, Org. Biomol. Chem. 2003, 1, 834-849).

No Mukaiyama aldol reactions have been described so far with compounds of formula II. Surprisingly, it has been found that N-benzyl-protected dialkyl acetal derivatives underwent the desired aldol reaction with high diastereoselectivity. The process for the preparation of compounds of formula I

wherein

R1 is Ci-4 alkyl, C3-6 cycloalkyl-C1-4 alkyl or aryl-Q.4 allcyl;

R2 is Ci-4 alkyl, benzyl, substituted benzyl or allyl;

R3 is Ci-4 alkyl or allyl;

R4 is Q-4 alkyl, allyl, benzyl or substituted benzyl;

R4 is benzyl or substituted benzyl; or

R1 and R4 together form a (CH2) 3-group;

comprises the reaction of a compound of formula II

wherein R1, R3, R4 and R4 are as defined above;

with a compound of formula III

O-R5

wherein R2 is as defined above;

R5 is a trialkylsilyl group;

in the presence of a Lewis acid and an organic solvent.

The term "Ci-4 alkyl" as used herein denotes straight or branched chain hydrocarbon residues containing 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl or tert-butyl. Ci-4 alkyl in R1 is methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl (the R or S isomer), isobutyl or tert-butyl. Preferred, C1^ alkyl in R1 is methyl, ethyl, isopropyl or sec- butyl (the R or S isomer); most preferably it denotes a (S)-sec-butyl group as depected in Example 1-12.

Ci-4 alkyl in R2 is preferably methyl, ethyl or tert-butyl, most preferably it denotes a tert-butyl group.

Ci-4 alkyl in R3 is preferably methyl or ethyl; most preferably it denotes a methyl group.

Q-4 alkyl in R4 is preferably methyl or ethyl; most preferably it denotes a methyl group.

The term "C3-6 cycloalkyl-Ci.4 alkyl" as used herein denotes a C3-6 cycloalkyl (cyclopropyl, cyclobutyl, cyclopentyl or cyclohexyl) linked to a Q-4 alkyl group as defined above. Preferably the term "C3-6 cycloalkyl-Q^ alkyl" as used herein denotes to a cyclohexylmethyl group.

The term "aryl-Q.4 alkyl" as used herein denotes a aryl group as defined below linked to a Ci-4 alkyl group as defined above. Preferably the term "aryl-Q.4 alkyl" as used herein denotes to a benzyl group.

The term "aryl" as used herein denotes an optionally substituted phenyl and naphthyl, both optionally benz-fused to an optionally substituted saturated, partially unsaturated or aromatic monocyclic, bicyclic or tricyclic heterocycle or carbocycle e.g. to cyclohexyl or cyclopentyl. Preferably the term "aryl" as used herein denotes to a phenyl group.

The term "substituted benzyl" as used herein for the substituents R2, R4 and R4 , denotes to the following substituents attached to the benzyl group: 2,4,6-trimethyl, 3-methoxy, 4-methoxy, 2,4-dimethoxy, 3,4-dimethoxy, 3,5-dimethoxy, 2-nitro, 4-nitro, 2,4-dinitro, 4-bromo, 4-phenyl and 3,4-methylene-dioxy.

The term "trialkylsilyl group" as used herein denotes a Si(Ci-6 alkyl)3, group wherein Ci-6 alkyl denotes straight or branched chain hydrocarbon residues containing 1 to 6 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, pentyl or hexyl. Preferably the term "trialkylsilyl group" denotes the following groups: dimethyl-tert-butyl-silyl, trimethyl-silyl or triethyl-silyl, most preferably it denotes a dimethyl-tert-butyl-silyl group. - A -

The term "Lewis acid" as used herein denotes to BF3, TMSOTf, TiCl4 or the corresponding solvent complexes, such as BFs-OEt2 or BF3-DMF, preferably BF3-DMF.

The term "organic solvent" as used for the synthesis of compound of formula I denotes to solvents, such as dichloromethane MeCN, THF, DMF (N,N- dimethylformamide), CHCI3, toluene or dichlorethane . Most preferably, dichloromethane maybe used as organic solvent.

The term "organic solvent" as used for the synthesis of a compound of formula II (reaction of the compound of formula IV and V) denotes alcohols, such as methanol, ethanol, propanol and butanol. In a preferred embodiment the alcohol depends on the substituent R3. If, for example, R3 is methyl the solvent is methanol.

The term "organic solvent" as used for the synthesis of the compound of formula II (reaction of the compound of formula VT and benzaldehyde) denotes a chlorinated solvent, such as dichloromethane, trichlormethane or dichlorethane. Most preferably, dichloromethane maybe used as organic solvent.

The term "acid" as used herein denotes HCl, HBr, H2SO4, CF3SO3H or p-Toluenesulfonic acid. Most preferably the term "acid" denotes H2SO4 or HCl.

The term "mineral acid" as used herein means HCl, HBr, H2SO4 or CF3SO3H, preferably HCl or H2SO4.

The term "reducing agent" as used herein denotes NaHB(OAc)3 or NaBH4. Most preferably the term "reducing agent" denotes NaHB(OAc)3.

The term "base" as used herein denotes typical N-containing organic bases, such as Me3N, Et3N, or pyridine. Most preferably, the term "base" denotes to Et3N.

The synthesis of the compound of formula I is carried out at a temperature range of -4O0C to 70°C, preferably at a temperature range of -200C to 300C, and most preferably at a temperature range of - 1O0C to 1O0C.

In a preferred embodiment of the invention the process for the preparation of the compound of formula II comprises the reaction of a compound of formula IV

wherein R1 is C1-4 alkyl, C3-6 cycloalkyl-Ci-4 alkyl or aryl-C1-4 alkyl; R4 is C1 -4 alkyl, allyl, benzyl or substituted benzyl;

R4 is benzyl or substituted benzyl, or

R1 and R4 together form a (CH2)3-group;

with a compound of formula V

HC(OR3)3 V

wherein R3 is C1-4 alkyl or allyl;

in the presence of an organic solvent and an acid;

or of a compound of formula VI

wherein R1 and R3 are as defined above;

in the presence of benzaldehyde or substituted benzaldehyde, a reducing agent, a base and an organic solvent.

In a preferred embodiment benzaldehyde is used.

The term "substituted benzaldehyde" as used herein for the synthesis of compounds of formula IV (from compounds of formula VI) , denotes to the following substituents attached to the phenyl group of the substituted benzaldehyde: 2,4,6- trimethyl, 3-methoxy, 4-methoxy, 2,4-dimethoxy, 3,4-dimethoxy, 3,5-dimethoxy, 2-nitro, 4-nitro, 2,4-dinitro, 4-bromo, 4-phenyl and 3,4-methylene-dioxy.

The substituted benzaldehyde is either commercially available or may be alternatively synthesized according to methods known from textbooks on organic chemistry (e.g. J. March (1992), "Advanced Organic Chemistry: Reactions, Mechanisms, and Structure", 4th ed. John Wiley & Sons).

In a further preferred embodiment of the invention the process is carried out wherein

R1 is methyl, ethyl, isopropyl or sec-butyl; R2 is methyl, ethyl or tert-butyl; R3 is methyl or ethyl; R4 is Ci-4 allcyl, ally! or benzyl; R4 is benzyl; R5 is dimethyl- tert-butyl- silyl, trimethyl- silyl or triethyl-silyl; the Lewis acid is BF3, TMSOTf, TiCl4, BF3OEt2 or BF3.DMF. In a further preferred embodiment of the invention the process is carried out wherein R1 is (S)-sec-butyl; R2 is tert-butyl; R3 is methyl; R4 is methyl; R4 is benzyl; R5 is dimethyl-tert-butyl-silyl; the Lewis acid is BF3.DMF. The compounds of formula I are new and therefore form part of the invention. Preferred are compounds of formula I

wherein R1 is Ci-4 alkyl, C3-6 cycloalkyl-Ci-4 alkyl or aryl-Ci-4 alkyl; R2 is Ci-4 alkyl, benzyl, substituted benzyl or allyl; R3 is Ci-4 alkyl or allyl; R4 is Ci-4 alkyl, allyl, benzyl or substituted benzyl; R4 is benzyl or substituted benzyl; or R1 and R4 together form a (CH2)3-group. Also preferred are compounds of formula I wherein R1 is methyl, ethyl, isopropyl, sec-butyl, cyclohexylmethyl, and benzyl R2 is methyl, ethyl or tert-butyl; R3 is methyl or ethyl; R4 is methyl, ethyl, allyl or benzyl; R4 is benzyl. A further preferred embodiment of the invention is a compound of formula I wherein R1 is (S)-sec-butyl; R2 is tert-butyl; R3 is methyl; R4 is methyl; R4' is benzyl. The compounds of formula II are new and therefore form part of the invention. Preferred are compounds of formula II

R ■

wherein R1 is C1-4 alkyl, C3-6 cycloalkyl-C1-4 alkyl or aryl-C1-4 alkyl; R3 is C1-4 alkyl or allyl; R4 is C1-4 alkyl, allyl, benzyl or substituted benzyl; R4 is benzyl or substituted benzyl; or R1 and R4 together form a (CH2)3-group. A further preferred embodiment of the invention are compounds of formula II wherein R1 is methyl, ethyl, isopropyl or sec-butyl; R3 is methyl or ethyl; R4 is methyl, ethyl, allyl or benzyl; and R4 is benzyl. A further preferred embodiment of the invention are compounds of formula II wherein R1 is (S)-sec-butyl; R3 is methyl; R4 is methyl; and R4 is benzyl. The compounds of formula IV are new and therefore form part of the invention. Preferred are compounds of formula IV

wherein R1 is Ci-4 alkyl, C3-6 cycloalkyl-C1-4 alkyl or aryl-C^ alkyl; R4 is C1-4 alkyl, allyl, benzyl or substituted benzyl; R4 is benzyl or substituted benzyl, or R1 and R4 together form a (CH2)3-group. A further preferred embodiment of the invention are compounds of formula IV wherein R1 is methyl, ethyl, isopropyl or sec-butyl; R4 is methyl, ethyl, allyl or benzyl; and

R4 is benzyl.

A further preferred embodiment of the invention are compounds of formula IV wherein

R1 is (S)-sec-butyl;

R4 is methyl; and

R4 is benzyl.

General synthesis of compounds of formula IV, wherein

R1 is Q-4 alkyl, C3-6 cycloalkyl-Ci-4 alkyl or aryl-C1-4 alkyl;

R4 is Ci-4 alkyl, allyl, benzyl or substituted benzyl;

R4 is benzyl or substituted benzyl; or

R1 and R4 together form a (CH2)3-group:

R' R4^ M N 0 H IV R4

The starting material compound of formula a, wherein R is C1.4 alkyl, C3-6 cycloalkyl-Ci-4 alkyl or aryl-Q.4 alkyl, is either commercially available or can be synthesized according to methods well known to the skilled artisan and as for example disclosed in textbooks on organic chemistry (e.g. J. March (1992), "Advanced Organic Chemistry: Reactions, Mechanisms, and Structure", 4 ed. John Wiley & Sons). General synthesis of compounds of formula VI, wherein

R1 is Ci-4 alkyl, C3-6 cycloalkyl-Q^ alkyl or aryl-C1-4 alkyl;

R3 is Ci-4 alkyl or allyi:

I OLJ a) reduction R HC(OR )3

O b) oxidation I H add

The starting material compound of formula d, wherein R1 is C1.4 alkyl, C3-6 cycloalkyl-Ci-4 alkyl or aiyl-Ci-4 alkyl, is either commercially available or can be synthesized according to methods well known to the skilled artisan and as for example described in textbooks on organic chemistry (e.g. J. March (1992), "Advanced Organic Chemistry: Reactions, Mechanisms, and Structure", 4 ed. John Wiley & Sons).

Compound of formula e is reacted with a compound of formula V, wherein R3 is Ci-4-alkyl or allyl, to obtain a compound of formula f (see also experimental part; example 3).

The compounds of formula I are important building blocks for the production of useful products in the chemical, agricultural and in the pharmaceutical industry. In particular they are useful for the production of anticancer substances as for example Dolastatin 10 or derivatives thereof as for example described in G.R. Pettit, "The Dolastatins", Progress in the Chemistry of Organic Natural Compounds, Springer, Vienna 1997, Vol. 70, 1-79, or in WO 03/008378.

Therefore, another embodiment of the present invention is the process as described above, wherein a compound of formula I is further reacted to give a compound of formula A

wherein

a) the benzyl or substituted benzyl group of R4 in formula I is cleaved in the presence of hydrochloric acid, hydrogen and a palladium catalyst to give a compound of formula I-A

b) said compound of formula I-A is further reacted with an N-protected valine derivative to give, after N-deprotection, a compound of formula B,

c) said compound of formula B is further reacted with a compound of formula C

to give a compound of formula D

d) the compound of formula D is further reacted with a compound of formula E to give a compound of formula A; and

R1, R2, R3 and R4 are as defined herein before;

R7, R8, R9 and R10 independently from each other represent alkyl; and

R11 is phenylalkyl-, or phenyldialkyiamino or phenylalkyloxy, having (C1-C4)- alkylene and wherein the phenyl group optionally may be substituted with one, two or three substituents selected from the group consisting of halogen, aLkoxycarbonyl, sulfamoyl, alkylcarbonyloxy, carbamoyloxy, cyano, mono- or di-alkylamino, alkyl, alkoxy, phenyl, phenoxy, trifluoromethyl, trifluoromethoxy, alkylthio, hydroxy, alkylcarbonylamino, 1,3-dioxolyl, 1,4-dioxolyl, amino and benzyl.

In a preferred embodiment according to the present invention, the N-protected valine derivative in step b) of the process as described above is the compound of formula F,

Reactions to deprotect N-protected amino acids, as for example valine and/or derivatives thereof as mentioned above are well known to the skilled artisan. According to the present invention, said deprotection of the N-protected valine derivative according to step b) of the process described above is preferably carried out by hydrogenolysis.

Still another embodiment of the present invention is the process as described above, wherein

R1 is sec-butyl;

R2 is tert-butyl; R3, R4, R7, R8, R9, and R10 are methyl; and R11 is 2-(3-hydroxyphenyl) ethyl-methyl amino.

Still another embodiment of the present invention is the process as described above for the manufacture of the compound of formula A-I

Yet another embodiment of the present invention is the use of the process according to the present invention in the manufacture of the compounds of formula A as defined above. Yet another embodiment of the present invention is the use of the process according to the present invention in the manufacture of the compound of formula A-I as defined above. In the following examples the abbreviations used have the following significations. NMR nuclear magnetic resonance spectroscopy IR infra red spectroscopy HV high vacuum min minute(s) h hour(s) RT room temperature Me methyl Et ethyl Example 1

(lS,2S)-(l-Hydxoxymethyl-2-methyl-butyl)-niethyl-carbamic acid tert-butyl ester

39.3g Boc-Melle-OH (0.160 mol; Synthetech) were dissolved in 160ml THF and cooled to 00C. 240ml IM BH3-THF (0.24 mol; Fluka) were added at 00C over 1 h and the clear, colorless reaction mixture was warmed up and stirred at RT for 1 h. The reaction mixture was again cooled to 00C, 100ml deionized water were carefully added at 0 - 50C over 0.5 h and after warming up to RT stirring was continued for 1 h. To the colorless solution were added 250ml 10% Na2CO3 all at once and after stirring for 1 h the reaction mixture was extracted with 1000ml and 500ml ethyl acetate. The organic layers were washed with brine and dried (Na2SO4). Removal of the solvent by rotary evaporation gave 36.9g (99.7%) product as colorless oil.

Example 2

(lS,2S')-(l-Formyl-2-methyl-butyl')-methyl-carbamic acid tert-butyl ester

To a solution of 37.Og Boc-N-methyl-isoleucinol (160 mmol) in 160ml dichloromethane was added a solution of 5.4g NaHCO3 (64 mmol) and 1.9g KBr (16 mmol) in 160ml deionized water. The reaction mixture was cooled to O0C and after the addition of 125mg 2,2,6,6-tetramethyl-piperidin-l-oxyl (TEMPO, 0.8 mmol), 122.6g 10.2% aqueous sodium hypochlorite (176 mmol Cl2) were added under stirring over 2.5 h at 0-5°. After additional stirring for 30 min the excess of NaOCl was destroyed by the addition of ca. 1ml 38% aqueous sodium bisulfite and the reaction mixture was warmed up to 20°. The aqueous layer was extracted with 160ml dichloromethane and the organic layers were washed with 10% brine and dried (Na2SO4). Removal of the solvent by rotary evaporation afforded 35.7g (97.2%) crude product as a light orange oil. Example 3

( 1 S,2S) - ( 1 -Dimethoxymet3iyl-2-metib.yl-butyl) -methyl- amine hydrochloride

35.6g Crude aldehyde (160 mmol) were dissolved in 200ml methanol and cooled to ~15°C. 111ml 2.8M HCl-MeOH (0.31 mol HCl) were added all at once and the yellowish solution was stirred at RT for 2 h. 155ml Trimethyl orthoformate (1.42 mol; Fluka) were now added and the reaction mixture was stirred at RT over night (18 h). The solvent and the excess of the orthoester were removed by rotary evaporation (40°C/> 10 mbar) and the resulting beige, crystalline residue (33.7g) was dissolved in ca. 310ml isopropyl acetate at ~70°C. After cooling to RT and crystallization at 00C for 17 h the crystal suspension was filtered and dried (50°C/10 mbar/16 h) affording 29.6g product as white needles, mp. 127-128°C. 1H-NMR:

Example 4

(lS,2S)-Benzyl-(l-dimethoxymethyl-2-methyl-butyl>)-met 3iyl-amine

To a solution of 31.76g the above described hydrochloride (150 mmol) in 600ml dichloromethane were added 15.94g triethylamine (157.5 mmol) and 17.51g benzaldehyde (165 mmol) and the clear light orange solution was stirred at RT for 1 h. 40.16g sodium triacetoxyborohydride (180 mmol; Aldrich) were added under ice cooling and the white suspension was stirred at RT for 24 h. The reaction mixture was washed with 600ml 10% Na2CO3 and twice with 300ml 10% brine. All three aqueous layers were extracted sequentially with 300ml dichloromethane and the combined organic layers were dried over Na2S(X Filtration and removal of the solvent by rotary evaporation (45°C/> 10 mbar) gave 41.3g orange oily residue. Purification by vacuum distillation gave 38.4g (96.5%) product, as colorless oil, b.p. 85-87°C/0.05 mbar. 1H-NMR:

Example 5

N-Benzyl-L-isoleucine (Bn-IIe-OH)

65.6g L-Isoleucine (500 mmol; Senn Chemicals) were added in portions to 250ml 2N NaOH (500 mmol) under stirring. After complete dissolution of the amino acid 53.1g benzaldehyde (500 mmol) were added all at once and stirring was continued at RT for 0.5 h. 5.7g Sodium borohydride (150 mmol) were now added under stirring in five portions at 5-15°C and stirring at RT was continued for 3.5 h. The reaction mixture was diluted with 250ml deionized water and extracted twice with 250ml diethyl ether. The clear aqueous layer (pH ~14) was now slowly neutralized under vigorous stirring with ca. 400ml 2N HCl to pH = 7 and the white, viscous suspension was stirred at RT for 0.5 h. After filtration and washing with deionized water (2 x 250ml), the filter cake was dried (70 h and 70°C/10 mbar/20 h) to yield 103.2g (93.2%) product as a white powder.

Example 6

N-Benzyl-N-methyl-L-isoleucine (Bn-MeIIe-OH)

To 110.7g of above described N-benzyl-isoleucine (0.50 mol) were added 69.Og formic acid (1.50 mol) and 49.4g formaldehyde 36.5% in water (0.60 mol) and the clear, colorless reaction mixture was heated under stirring to ~90°C for 2 h. The reaction mixture was concentrated by rotary evaporation (60°C/25 mbar) and the residue was triturated under stirring (~15 min) with 250ml acetone. After evaporation of the solvent, triturating was repeated twice using a total of 500ml acetone. Evaporation of the solvent (50°C/10 mbar) gave 129.9g white, crystalline residue which was stirred with 200ml acetone for 1 h at RT and 3 h at -2O0C. The crystal suspension was filtered, washed with cold acetone and dried (16 h / 500C / 10 mbar) affording 103.9g (88.3%) product as a white, crystalline powder.

Example 7

N-Benzyl-N-methyl-L-isoleucinol

To a grey suspension of 22.8g lithium aluminum hydride (0.60 mol) in 600ml tetrahydrofuran were added at 0-100C 94.1g N-ben∑yl-N-methyl-L-isoleucine (0.40 mol) in 6 portions over 20 min. The ice-methanol bath was removed and the reaction mixture was heated up and refluxed for 1.5 h. The reaction mixture was again cooled to 00C, diluted with 450ml diethyl ether and then hydrolyzed by the slow addition of 23ml deionized water. After the addition of 23ml 15% aqueous NaOH at 00C a thick grey suspension was formed. 70ml Deionized water were added over 0.5 h and the color of the suspension turned from grey to white. Stirring was continued at 00C for 15 min and at RT for 0.5 h. The white precipitate was filtered off, washed with 270ml diethyl ether and the filtrate was evaporated (35°C/> 10 mbar) affording 85.1g (96.1%) of the product as colorless oil.

Example 8

(2S,3S)-2-(Benzyl-methyl-amino')-3-methyl-pentanal

To a stirred solution of 36ml oxalyl chloride (0.42 mol; Fluka) in 1100ml dichloromethane were added at -700C a solution of 44ml dimethyl sulfoxide (0.62 mol) in 800ml dichloromethane over 0.5 h. After stirring at -70° for 15 min a solution of 77.5g N- benzyl-N-methyl-isoleucinol (0.35 mol) in 700ml dichloromethane was added at -700C over ~0.5 h and stirring was continued for 15 min. After the addition of 234ml triethylamine (1.68 mol) at -65°C stirring was continued for 5 min and the white suspension stirred at -500C for 1 h. The dry ice-bath was removed and 3000ml deionized water was added drop wise and under stirring while the reaction mixture was warmed up to RT. The organic layer was washed twice with 2000ml 10% brine and the organic layer was dried (Na2SO4). Removal of the solvent by rotary evaporation (40°C/> 10 mbar/0.1 mbar, 2h) yielded 76.9g (100.2%) yellow oily product which was used without purification in the next step.

Example 9

Benzyl-(dS,2S)-l-dimethoxymethyl-2-methyl-butyl)-methyl-a mine

To 76.9g of the above described aldehyde (0.35 mol) dissolved in 350ml methanol were added drop wise and under cooling 70ml cone. H2SO4 (~1.30 mol). After stirring for 0.5 h 350ml trimethyl orthoformate (3.20 mol; Fluka) were added all at once and stirring at RT was continued for 3 h. The reaction mixture was diluted with 2000ml ethyl acetate and washed with 2000ml 10% Na2CO3 and 2000ml 10% brine. The organic layer was dried (Na2SO^ and evaporated by rotary evaporation (45°C/> 10 mbar) affording 91.9g yellow oil. Purification by a vacuum distillation gave 86.Og (92.6%) product as a light yellow oil, b.p. 106°C/0.1 mbar. 1H-NMR:

Example 10

( 1 -tert-Butoxy-vinyloxy) -tert-butyl-dimethyl-silane

To a stirred solution of 58.2g diisopropylamine (575 mmol) in 500ml tetrahydrofuran were added at O0C 344ml 1.6M BuLi in hexane (550 mmol) over 20 min. After stirring for 15 min the solution was cooled to -700C and 58.1g tert-butγl acetate (500 mmol; Fluka) were added at -7O0C over 15 min and stirring continued for 15 min. After the addition of 75ml HMPA (Fluka) a solution of 81.6g tert- butyldimethylchlorosilane (525 mmol; Fluka) in 100ml tetrahydrofaran was added at - 700C over 15 min and the reaction mixture was warmed to RT over ~1 h. The reaction mixture was concentrated by rotary evaporation (40°C/> 10 mbar) and the honey-oily residue was partitioned between 1000ml hexane and 1000ml deionized water. The organic layer was washed with 10% brine (2 x 500ml) and dried (Na2SC^) affording after removal of the solvent by rotary evaporation (40°C/> 10 mbar) 116.1g bright yellow oil. Purification by vacuum distillation gave 106.Og (92.0%) product as a colorless oil, b.p. 53-54°C/2.0 mbar.1H-NMR:

Example 11

(3R4S,5S)-4-(Benzyl-mei3iyl-ammo')-3-methoxy-5-methyl-hep tanoic acidtert-butyl ester (Bn-DiI-OtBu)

To a stirred solution of the above described 13.27g dimethylacetal (50 mmol) and the above described 17.28g TBS-silylketene acetal (75 mmol) in 200ml dichloromethane was added at O0C a solution of 8.04g N,N-dimethylformamide and 14.19g boron trifluoride ethyl etherate (100 mmol = 12.56ml; Fluka) in 50ml dichloromethane over 15 min. After stirring at 0°C for 24 h the reaction mixture was washed with 250ml 10% Na2CCb and with 10% brine (2 x 125ml). The organic layer was (Na2SO4) and the solvent was removed by rotary evaporation (40°C/>10 mbar/0.1 mbar, 2h) yielding 17.5g (100.1%) crude product as a yellow oil which was used without purification in the next step. OD [α]D = -18.0° (CHCl3; c = 1). 1H-NMR:

Example 12

(3R,4S,5S)-3-Met3ioxy-5-methyl-4-methylainmo-heptanoic acid tert-butyl ester hydrochloride fH-Dil-OtBu.HCl)

To a stirred solution of 17.5g of the above described ester (50 mmol) in 250ml ethanol were added 0.87g Pd-C 10% (Degussa) and 4.59ml 37% HCl (55 mmol). The black suspension was hydrogenated under vigorous stirring at RT for 18 h. The flask was flashed with Ar and the black suspension was filtered. After removal of the solvent by rotary evaporation (40°C/> 10 mbar) the white crystalline residue (14.54g) was dissolved in 350ml ethyl acetate at ~80°C. After cooling to RT and crystallization under stirring at 00C for 17 h the crystal suspension was filtered, washed with -20° cold ethyl acetate and dried (50°C/10 mbar/16 h) affording 12.87g (87.0% over two steps) white crystalline product, m.p. 153-154°C (dec). OD [α]D = +6.71° (CHCl3; c = 1). MS ([M+l]+ of the free base). 1H-NMR:

Example 13

((S)-l-Hvdroxyτnethyl-2-methyl-proρyl)-methyl-carbamic acid tert-butyl ester

20.Og Boc-MeVal-OH (86.5 mmol; Fluka) were dissolved in 80ml THF and cooled to 00C. 130ml IM BH3-THF (0.13 mol; Fluka) were added at 00C over 1 h and the clear, colorless reaction mixture was warmed up and stirred at RT for 1 h. The reaction mixture was again cooled to 00C, 75ml deionized water were carefully added at 0 - 5°C over 0.5 h and after warming up to RT stirring was continued for 1 h. To the colorless solution were added 150ml 10% Na2CO3 all at once and after stirring for 1 h the reaction mixture was extracted with 600ml and 300ml ethyl acetate. The organic layers were washed with brine and dried (Na2SO:).). Removal of the solvent by rotary evaporation gave 17.4g (94%) product as colorless oil. 1H-NMR: Example 14

((S)-I -Formγl-2-methyl-ρropyl)-methyl-carbamic acid tβrt-butyl ester

To a solution of 10.5g Boc-N-methyl-valinol (48.3 mmol) in 50ml dichloromethane was added a solution of 1.63g NaHCO3 (19.3 mmol) and 0.58g KBr (4.8 mmol) in 50ml deionized water. The reaction mixture was cooled to 00C and after the addition of 77mg 2,2,6,6-tetramethyl-piperidin-l-oxyl (TEMPO, 0.48 mmol), 36.6g 10.3% aqueous sodium hypochlorite (53.1 mmol Cl2) were added under stirring over 2.5 h at 0-5°. After additional stirring for 30 min the excess of NaOCl was destroyed by the addition 38% aqueous sodium bisulfite and the reaction mixture was warmed up to 20°. The aqueous layer was extracted with 50ml dichloromethane and the organic layers were washed with 50ml 10% brine and dried (Na2SO4). Removal of the solvent by rotary evaporation afforded 9.9g (95%) crude product as a light orange oil, [α]D = -130 (CHCl3; c = 1).

1H-NMR: Example 15

((S)- l-Dimethoxymethyl-2-methyl-propyl)-methyl-arnine hydrochloride

5.Og Crude Boc-N-methyl-valinal (23.2 mmol) were dissolved in 40ml methanol and cooled to ~15°C. A solution of 3.3ml (46.4 mmol) acetyl chloride in 10ml methanol was added all at once and the yellowish solution was stirred at RT for 1 h (gas evolution). 22.2g Trimethyl orthoformate (209 mmol) were now added and the reaction mixture was stirred at RT over night (18 h). The solvent and the excess of the orthoester were removed by rotary evaporation (40°C/> 10 mbar) and the resulting beige, crystalline residue (4.6g) was dissolved in ca. 45ml isopropyl acetate at ~70°C. After cooling to RT and crystallization at -2O0C for 17 h the crystal suspension was filtered and dried (50°C/10 mbar/16 h) affording 3.2g (69%) product as greenish needles, [α]D = 40.3 (CHCl3; c = 1). 1H-NMR:

Example 16

Benzyl-((S)-l-dimethoxymethyl-2-methyl-t>roρyl)-methy l-amine

To a solution of 7.13g the above N-Me- Valinal dimethylacetal hydrochloride (36.1 mmol) in 140ml dichloromethane were added 3.83g triethylamine (37.9 mmol) and 4.21g benzaldehyde (39.7 mmol) and the solution was stirred at RT for 0.5 h. 10.2g sodium triacetoxyborohydride (43.3 mmol; Aldrich) were added under ice cooling and the white suspension was stirred at RT for 22h. The reaction mixture was washed with 100ml 10% Na2CC^ and twice with 100ml 10% brine. All three aqueous layers were extracted sequentially with 200ml dichloromethane and the combined organic layers were dried over Na2SO4. Filtration and removal of the solvent by rotary evaporation (45°C/> 10 mbar) gave 9.54g orange oily residue. Purification by vacuum distillation gave 8.34g (92%) product, as light yellow oil, b.p. 86°C/0.2 mbar, [α]D = -21.8 (CHCl3; c = 1). 1H-NMR:

Example 17

(3R,4S)-4-(Benzyl-methyl-amino)-3-methoxy-5-methyl-hexano ic acid tert-butyl ester

To a stirred solution of the above described dimethylacetal 7.54g (30 mmol) and the above described TBS-silylketene acetal 10.4g (45 mmol) in 110ml dichloromethane was added at 00C a solution of 4.83g (66 mmol) N,N-dimethylformamide and 8.52g boron trifluoride ethyl etherate (60 mmol = 12.56ml; Fluka) in 30ml dichloromethane over 15 min. After stirring at O0C for 69 h the reaction mixture was washed with 150ml 10% Na2CO3 and with 10% brine (2 x 80ml). The organic layer was dried (Na2SO4) and

the solvent was removed by rotary evaporation (40°C/>10 mbar/0.1 mbar, 2h) yielding

10. Ig (100%) crude product as a yellow oil which was used without purification in the

next step, [α]D = -20.2 (CHCl3; c = 1). 1H-NMR:

Exmaple 18

(3R,4S)-3-Methoxy-5-methyl-4-methylamino-hexanoic acid tert-butyl ester hydrochloride

To a stirred solution of 10.Og of the above described ester (30 mmol) in 150ml ethanol were added l.Og Pd-C 10% (Degussa) and 2.6ml 37% HCl (31.2 mmol). The black suspension was hydrogenated under vigorous stirring at RT for 18 h. The flask was flashed with Ar and the black suspension was filtered. After removal of the solvent by rotary evaporation (40°C/> 10 mbar) the white crystalline residue (8.76g) was dissolved in 25ml hot isopropyl acetate at ~80°C. After cooling to RT and crystallization under stirring at -15°C for 17 h the crystal suspension was filtered, washed with -20°cold isopropyl acetate and dried (50°C/10 mbar/16 h) affording 4.84g (57.0% over two steps) white crystalline product, [α]D = 7.9 (CHCl3; c = 1).1H-NMR:

Example 19

((S)-2-Hvdroxy-l-methyl-etliyl)-methyl-carbamic acid tert-bntyl ester

20.3g Boc-MeAla-OH (100 mmol; Fluka) were dissolved in 80ml THF and cooled to 00C. 150ml IM BH3-THF (150 mmol; Fluka) were added at 00C over 1 h and after additional stirring at 00C for 1 h, 65 ml deionized water were added carefully at 0 - 5°C. After warming up to RT 160ml 10% Na2CO3 were added and stirring continued for 1 h. The reaction mixture was extracted with 500ml and 400ml ethyl acetate and the organic layers were washed with brine and dried (Na2SO4). Removal of the solvent by rotary evaporation gave 18.5g (98%) product as a colorless oil, [α]π = -6.1 (CHCI3; c = 1).

1H-NMR: Example 20

Methγl-f fS)-l-methyl-2-oxo-ethyl)-carbamic acid tert-butyl ester

To a solution of 18.0g Boc-N-methyl-alaninol (95 mmol) in 95ml dichloromethane was added a solution of 3.2g NaHCO3 (38 mmol) and 1.14g KBr (9.5 mmol) in 95ml deionized water. The reaction mixture was cooled to 00C and after the addition of 152mg 2,2,6,6-tetramethyl-piperidin-l-oxyl (TEMPO, 0.95 mmol), 72g 10.3% aqueous sodium hypochlorite (105 mmol Cl2) were added under stirring over 2.5 h at 0-5°. After additional stirring for 30 min the excess of NaOCl was destroyed by the addition 38% aqueous sodium bisulfite (ImI) and the reaction mixture was warmed up to 20°. The aqueous layer was extracted with 100ml dichloromethane and the organic layers were washed with 100ml 10% brine and dried (Na2SO4). Removal of the solvent by rotary evaporation afforded 14.4g (80%) crude product as a light orange oil, [OC]D = -82 (CHCI3; C = I)- 1H-NMR: Example 21

((S)-2,2-Dimethoxy-l-methyl-emyl)-methyl-amme hydrochloride

13. Ig Crude Boc-N-methyl-alaninal (70,mmol) were dissolved in 100ml methanol and cooled to ~15°C. A solution of Hg (140 mmol) acetyl chloride in 30ml methanol was added all at once and the yellowish solution was stirred at RT for 1 h (gas evolution). 67.52g Trimethyl orthoformate (630 mmol) were now added and the reaction mixture was stirred at RT over night (18 h). The solvent and the excess of the orthoester were removed by rotary evaporation (40°C/> 10 mbar) and the resulting 11.9 (100%) beige, crystalline residue was crystallized from 120ml hot isopropyl acetate yielding after stirrung at -200C for 17 h 8.4g (71%) beige product, [α]D = 10.8 (CHCl3; c = 1). 1H-NMR:

Example 22

Benzyl- { (S ) -2,2-dimethoxy- 1 -methyl-ethyl) -metfayl-amine

To a solution of 7.63g the above N-Methyl-alaninal dimethylacetal hydrochloride (45 mmol) in 180ml dichloromethane were added 4.78g triethylamine (47.2 mmol) and 5.25g benzaldehyde (49.5 mmol) and the solution was stirred at RT for 0.5 h. 12.7g sodium triacetoxyborohydride (54 mmol; Aldrich) were added under ice cooling and the white suspension was stirred at RT for 22h. The reaction mixture was washed with 180ml 10% Na2CO3 and twice with 90ml 10% brine. All three aqueous layers were extracted sequentially with 100ml dichloromethane and the combined organic layers were dried over Na2SO4. Filtration and removal of the solvent by rotary evaporation (45°C/> 10 mbar) gave 10.0g orange oily residue. Purification by vacuum distillation gave 8.1g (80%) product, as light yellow oil, b.p. 119°C/0.8 mbar, [α]D = -2.2 (CHCl3; c = 1). 1H-NMR:

Example 23

(3R,4S)-4-(Benzyl-metJh.yl-amijio)-3-methoxy-pentanoic acid tert-butyl ester

To a stirred solution of the above described 2.9Og dimethylacetal (13 mmol) and the above described 8.99g TBS-silylketene acetal (39 mmol) in 50ml dichloromethane was added at 00C a solution of 5.7Og N,N-dimethylformamide (78 mmol) and 5.53g boron trifluoride ethyl etherate (39 mmol = 12.56ml; Fluka) in 13ml dichloromethane. After stirring at 00C for 24 h the reaction mixture was washed with 65ml 10% Na2COa and with 10% brine (2 x 30ml). The organic layer was dried (Na2SO4) and the solvent was removed by rotary evaporation (40°C/>10 mbar/0.1 mbar, 2h) yielding 4.66g crude product as a yellow oil which was chromatographed over silica (20Og) with toluene- ethyl acetate 19 : 1 (30ml fractions). Evaporation of fraction 21 - 40 gave 2.97g (74%) yellow oil. 1H-NMR:

Example 24

(3R,4S)-3-Metho:xy-4-methylammo-pentanoic acid tert-butyl ester hydrochloride

To a stirred solution of 1.5Ag of the above described ester (5 mmol) in 25ml ethanol were added 0.15g Pd-C 10% (Degussa) and 0.52g 37% HCl (5.2 mmol). The black suspension was hydrogenated under vigorous stirring at RT for 2 h. The flask was flashed with Ar and the black suspension was filtered. After removal of the solvent by rotary evaporation (40°C/> 10 mbar) the white crystalline residue (1.19g) was dissolved in hot acetonitrile (8ml) and crystallized at 00C yielding 1.02g (80%) beige product, [α]π = -6.2 (CHCl3; c = 1). 1H-NMR:

Example 25

(S)-2-Dimethoxymethγl-pyrrolidine hydrochloride

13.9g Crude Boc-prolinal (70 mmol; Omega Chem, freshly distilled) were dissolved in 11 OmI methanol and cooled to ~15°C. A solution of 11. Og (140 mmol) acetyl chloride in 30ml methanol was added all at once and the yellowish solution was stirred at RT for 1 h (gas evolution). 66.9g Trimethyl orthoformate (630 mmol) were now added and the reaction mixture was stirred at RT for 42 h. The solvent and the excess of the orthoester were removed by rotary evaporation (40°C/> 10 mbar) and the resulting 14.Og beige, crystalline residue was crystallized from 300ml hot ethyl acetate yielding after stirrung at 00C for 17 h 8.9g (70%) white needles, [α]D = -15.4 (CHCl3; c = 1). 1H-NMR:

Example 26

(S)-l-Benzyl-2-dimethoxymethyl-ρyrrolidine

To a solution of 8.2g of the above described prolinal dimethylacetal hydrochloride (45 mmol) in 150ml dichloromethane were added 4.78g triethylamine (47.2 mmol) and 5.25g benzaldehyde (49.5 mmol) and the solution was stirred at RT for 0.5 h. 12.7g sodium triacetoxyborohydride (54 mmol; Aldrich) were added under ice cooling and the white suspension was stirred at RT for 26h. The reaction mixture was washed with 180ml 10% Na2Cθ3 and twice with 90ml 10% brine. All three aqueous layers were extracted sequentially with 90ml dichloromethane and the combined organic layers were dried over Na2SU4. Filtration and removal of the solvent by rotary evaporation (45°C/> 10 mbar) gave 10.5g yellow oily residue. Purification by vacuum distillation gave 8.93g (84%) product, as a colorless oil, b.p. 120°C/0.4 mbar, [α]D = -73.8 (CHCl3; c = 1). 1H-NMR: I— I— I L=I

Example 27

(R)-3-rfS)-l-Benzyl-pyrrolidin-2-yl)-3-methoxyr-propionic acid tert-butyl ester

To a stirred solution of the above described dimethylacetal 4.71g (20 mmol) and the above described TBS-silylketene acetal 13.83g (60 mmol) in 75ml dichloromethane was added at 00C a solution of 6.43g (88 mmol) N,N-dimethylformamide and 11.35g boron trifluoride ethyl etherate (80 mmol) in 25ml dichloromethane. After stirring at 00C for 24 h the reaction mixture was washed with 100ml 10% Na2COs and with 10% brine (50ml). The organic layer was dried (Na2SO4) and the solvent was removed by rotary evaporation (40°C/>10 mbar/0.1 mbar, 2h) yielding 10.2g crude oily product as a ca. 2 : 1 mixture of two diastereoisomers. Chromatography over silica (70Og) with hexane-ethyl acetate 14 : 1 (200ml fractions) gave 2.49g oily (3R,4S)-diastereomer (39%; fractions 14- 30) and 1.23g (3S,4S)-diastereomer (19%; fractions 35-44). (3R,4S)-diastereomer: [α]D = -88.7 (CHCl3; c = 1)

(3R,4S)-diastereomer: 1H-NMR:

(3S,4S)-diastereomer: IH-NMR:

Example 28 (R)-3-Methoxy-3-fS)-pyrrolidin-2-yl-propionic acid tert-butyl ester hydrochloride

configurat d by X-ray

To a stirred solution of 1.92g of the above described ester (6 mmol) in 30ml ethanol were added 0.2Og Pd-C 10% (Degussa) and 0.62g 37% HCl (6.3 mmol). The black suspension was hydrogenated under vigorous stirring at RT for 2 h. The flask was flashed with Ar and the black suspension was filtered. After removal of the solvent by rotary evaporation (40°C/> 10 mbar) the white crystalline residue (1.57g) was dissolved in 7.5ml hot isopropyl acetate at ~80°C. Crystallization at -200C yielding 1.37g (86%) white crystalline product, [α]o = -36.4 (CHCI3; c = 1). 1H-NMR: