PREPARATION OF SUBSTITUTED ISOSERINE ESTERS USING METAL ALKOXIDES AND beta -LACTAMS

Abstract: A process for preparing N-acyl, N-sulfonyl and N-phosphoryl substituted isoserine esters in which a metal alkoxide is reacted with a beta -lactam.

Description: PREPARATION OF SUBSTITUTED ISOSERINE ESTERS USING METAL ALKOXIDES AND β-LACTAMS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part application of U.S. Serial No. 07/863,849, filed April 6, 1992, which was a continuation-in-part application of U.S. Serial No. 07/862,955, filed April 3, 1992, which was a continuation-in-part application of U.S. Serial No. 07/763,805, filed September 23, 1991, now abandoned. BACKGROUND OF THE INVENTION Three esters of N-acyl phenyl isoserine, taxol, taxotere and cephalomannine have been found to possess significant properties as antitumor . agents. This application describes a process for the preparation of N-acyl, N-sulfonyl and N-phosphoryl substituted isoserine esters, in general and to a semi-synthesis for the preparation of taxane derivatives such as taxol, taxotere and other biologically active derivatives involving the use of metal alkoxides and β-lactams, in particular. The taxane family of terpenes, of which taxol is a member, has attracted considerable interest in both the biological and chemical arts. Taxol is a promising cancer chemotherapeutic agent with a broad spectrum of antileukemic and tumor-inhibiting activity. Taxol has the following structure: SUBSTITUTE SHEET wherein Ph is phenyl and Ac is acetyl. Because of this promising activity, taxol is currently undergoing clinical trials in both France and the United States. The supply of taxol for these clinical trials is presently- being provided by the bark from Taxus brevifollia (Western Yew) . However, taxol is found only in minute quantities in the bark of these slow growing evergreens, causing considerable concern that the limited supply of taxol will not meet the demand. Consequently, chemists in recent years have expended their energies in trying to find a viable synthetic route for the preparation of taxol. So far, the results have not been entirely satisfactory. One synthetic route that has been proposed is directed to the synthesis of the tetracyclic taxane nucleus from commodity chemicals. A synthesis of the taxol congener taxusin has been reported by Holton, et al. in JACS 110. 6558 (1988). Despite the progress made in this approach, the final total synthesis of taxol is, nevertheless, likely to be a multi-step, tedious, and costly process. A semi-synthetic approach to the preparation of taxol has been described by Greene, et al. in JACS 110, 5917 (1988), and involves the use of a congener of taxol, 10-deacetyl baccatin III which has the structure of formula II shown below: SUBSTITUTE SHEET 10-deacetyl baccatin III is more readily available than taxol since it can be obtained from the needles of Taxus baccata. According to the method of Greene et al., 10-deacetyl baccatin III is converted to taxol by attachment of the C-10 acetyl group and by attachment of the C-13 β-amido ester side chain through the esterification of the C-13 alcohol with a β-amido carboxylic acid unit. Although this approach requires relatively few steps, the synthesis of the β-amido carboxylic acid unit is a multi-step process which proceeds in low yield, and the coupling reaction is tedious and also proceeds in low yield. However, this coupling reaction is a key step which is required in every contemplated synthesis of taxol or biologically active derivative of taxol, since it has been shown by Wani, et al. in JACS 93, 2325 (1971) that the presence of the β-amido ester side chain at C13 is required for anti-tumor activity. More recently, it has been reported in Colin et al. U.S. Patent No. 4,814,470 that taxol derivatives of the formula III below, have an activity significantly greater than that of taxol (I). OCOCgHg R' represents hydrogen or acetyl and one of R" and R" * represents hydroxy and the other represents tert-butoxy- SUBSTITUTESHEET carbonylamino and their stereoisomeric forms, and mixtures thereof. According to Colin et al., U.S. Patent 4,418,470, the products of general formula (III) are obtained by the action of the sodium salt of tert-butyl N-chlorocarbamate on a product of general formula: in which R' denotes an acetyl or 2,2,2-trichloroethoxy- carbonyl radical, followed by the replacement of the 2,2,2-trichloroethoxycarbonyl group or groups by hydrogen. It is reported by Denis et al. in U.S. Patent No. 4,924,011, however, that this process leads to a mixture of isomers which has to be separated and, as a result, not all the baccatin III or 10-deactylbaccatin III employed for the preparation of the product of general formula (IV) can be converted to a product of general formula (III). In an effort to improve upon the Colin et al. process, Denis et al. disclose a different process for preparing derivatives of baccatin III or of 10-deactyl- baccatin III of general formula SUBSTITUTESHEET C 6 in which R' denotes hydrogen or acetyl wherein an acid of general formula: in which R-^ is a hydroxy-protecting group, is condensed with a taxane derivative of general formula: OCOC 6 H 5 in which R 2 is an acetyl hydroxy-protecting group and R 3 is a hydroxy-protecting group, and the protecting groups R^, R 3 and, where appropriate, R 2 are then replaced by SUBSTITUTESHEET hydrogen. However, this method employs relatively harsh conditions, proceeds with poor conversion, and provides less than optimal yields. A major difficulty remaining in the synthesis of taxol and other potential anti-tumor agents is the lack of a readily available method for easy attachment, to the C-13 oxygen, of the chemical unit which provides the β-amido ester side chain. Development of such a process for its attachment in high yield would facilitate the synthesis of taxol as well as related anti-tumor agents having a modified set of nuclear substituents or a modified C-13 side chain. This need has been fulfilled by the discovery of a new, efficient process for attachment, to the C-13 oxygen, of the chemical unit which provides the β-amido ester side chain. Another major difficulty encountered in the synthesis of taxol is that known processes for the attachment of the β-amido ester side chain at C-13 are generally not sufficiently diastereoselective. Therefore the side chain precursor must be prepared in optically active form to obtain the desired diastereomer during attachment. The process of this invention, however, is highly diastereoselective, thus permitting the use of a racemic mixture of side chain precursor, eliminating the need for the expensive, time-consuming process of separating the precursor into its respective enantiomeric forms. The reaction additionally proceeds at a faster rate than previous processes, thus permitting the use of less side-chain precursor than has been required by such previous processes. SUMMARY OF THE INVENTION Among the objects of the present invention, therefore, is the provision of a process for the preparation of N-acyl, N-sulfonyl and N-phosphoryl esters SUBSTITUTESHEET of isoserine; the provision of a side chain precursor for the synthesis of taxane derivatives; the provision of a process for the attachment of the side chain precursor in relatively high yield to provide an intermediate which is readily converted to the desired taxane derivative; and the provision of such a process which is highly diastereo¬ selective. In accordance with the present invention, a process is provided for the preparation of isoserine esters having the formula comprising reacting a β-lactam with a metal alkoxide, the β-lactam having the formula and the metal alkoxide having the formula MOCE 1 E 2 E 3 wherein R-L is -OR 6 , -SR-, or -NRgRg; R 2 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; R 3 and R 4 are independently hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, or acyl, provided, however, that R and R 4 are not both acyl; SUBSTITUTESHEET R 5 is -COR 10 , -COOR 1Q , -COSR 10 , -CONR 8 R 10 , R 6 is hydrogen, alkyl, alkenyl, alkynyl, aryl, - heteroaryl, hydroxy protecting group, or a functional grou which increases the water solubility of the taxane derivative, R 7 is alkyl, alkenyl, alkynyl, aryl, heteroaryl, or sulfhydryl protecting group, R 8 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; Rg is an amino protecting group; R 10 is alkyl, alkenyl, alkynyl, aryl, or heteroaryl, R±l is alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR 1Q , or -NR 8 R 14 , R 12 and R 13 are independently alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR 10 , or -NR g R 14 , R 14 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; E^, E 2 and E 3 are independently hydrogen, hydrocarbon or cyclic, provided, at least one of E^, E and E 3 is other than hydrogen. Preferably, two of E j , E 2 , and E 3 together with the carbon to which they are attached comprise a mono- or polycyclic skeleton. In accordance with another aspect of the present invention, the metal alkoxide and β-lactam are selected so as to provide a process for preparing taxol, taxotere and other biologically active taxane derivatives having the following structural formula: SUBSTITUTESHEET wherein R ] _ - R 14 are as previously defined, R-L5 and R^g are independently hydrogen, hydroxy, lower alkanoyloxy, alkenoyloxy, alkynoyloxy, aryloyloxy or together form an oxo; R j 7 and R^g are independently hydrogen or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy or R-^- and R^ 8 together form an oxo; R 19 and R 20 are independently hydrogen or hydroxy or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy; R and R 22 are independently hydrogen or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy or R 21 and R 22 together form an oxo; R 2 is hydrogen or hydroxy or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy; or R 23 and R 24 together form.an oxo or methylene or R 23 and R 24 together with the carbon atom to which they are attached form an oxirane ring or R 23 and R 22 together with the carbon atom to which they are attached form an oxetane ring; 2 5 is hydrogen, hydroxy, or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy or SUBSTITUTESHEET R 26 is hydrogen, hydroxy, or lower alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy; or R 2 and R 5 taken together form an oxo; and R 27 is hydrogen, hydroxy or lower alkoxy, alkanoyloxy, alkenoyloxy, alkynoyloxy, or aryloyloxy. Briefly, therefore, the taxane derivatives are prepared by reacting a β-lactam (2) with a metal alkoxide having the bi-, tri- or tetracyclic taxane nucleus to form a β-amido ester intermediate. The intermediate is then converted to the taxane derivative. β-lactam (2) has the general formula: wherein R- j^ - R^ are as previously defined. The metal alkoxide preferably has the tricyclic taxane nucleus corresponding to the general formula: SUBSTITUTE SHEET wherein M is a metal, and 15-R27 are as Previously defined. Most preferably, the metal alkoxide has the tetracyclic taxane nucleus corresponding to metal alkoxide (3) wherein R 22 and R 23 together form an oxetane ring. Other objects and features of this invention will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION The present invention is directed to a process for preparing substituted isoserine esters, in general, and taxol, taxotere and other taxane derivatives which are biologically active using β-lactam (2), the structure of which is depicted hereinbelow: wherein R- j _, R 2 , R 3 , R 4 and R 5 are as previously defined. In accordance with the present invention, R 5 of β-lactam (2) is preferably -COR 10 with R 10 with R 10 being aryl, heteroaryl, p-substituted phenyl, or lower alkoxy, and most preferably phenyl, methoxy, ethoxy, tert-butoxy ("tBuO"; (CH 3 ) 3 CO-), or SUBSTITUTESHEET wherein X is Cl, Br, F, CH 3 0-, or N0 2 ~. Preferably R 2 and R 4 are hydrogen or lower alkyl. R 3 is preferably aryl, most preferably, naphthyl, phenyl, wherein X is as previously defined, Me is methyl and Ph is phenyl. Preferably, R± is selected from -ORg, -SR 7 or -NRgR g wherein Rg, R 7 and R 9 , are hydroxy, sulfhydryl, and amine protecting groups, respectively, and Rg is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl. Most preferably, R χ is -ORg wherein Rg is triethylsilyl ("TES"), 1-ethoxyethyl ("EE") or 2,2,2-trichloroethoxymethyl. The β-lactam alkyl groups, either alone or with the various substituents defined hereinabove are preferably lower alkyl containing from one to six carbon atoms in the principal chain and up to 15 carbon atoms. They may be straight or branched chain and include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, aryl, hexyl, and the like. The β-lactam alkenyl groups, either alone or with the various substituents defined hereinabove are preferably lower alkenyl containing from two to six carbon atoms in the principal chain and up to 15 carbon atoms. They may be straight or branched chain and include ethenyl, propenyl, isopropenyl, butenyl, isobutenyl, aryl, hexenyl, and the like. The β-lactam alkynyl groups, either alone or with the various substituents defined hereinabove are preferably lower alkynyl containing from two to six carbon atoms in the principal chain and up to 15 carbon atoms. They may be straight or branched chain and include ethynyl, propynyl, butynyl, isobutynyl, aryl, hexynyl, and the like. The β-lactam aryl moieties described, either alone or with various substituents, contain from 6 to 15 carbon atoms and include phenyl, α-naphthyl or β-naphthyl, etc. Substituents include alkanoxy, protected hydroxy, halogen, alkyl, aryl, alkenyl, acyl, acyloxy, nitro, amino, amido, etc. Phenyl is the more preferred aryl. As noted above, R of β-lactam (2) may be -ORg with Rg being alkyl, acyl, ethoxyethyl ("EE"), triethylsilyl ("TES"), 2,2,2-trichloroethoxymethyl, or other hydroxyl protecting group such as acetals and ethers, i.e., methoxymethyl ("MOM"), benzyloxymethyl; esters, such as acetates; carbonates, such as methyl carbonates; and alkyl and aryl silyl such as triethylsilyl, trimethylsilyl, dimethyl-t-butylsilyl, dimethylarylsilyl, dimethyl- heteroarylsilyl, and triisopropylsilyl, and the like. A variety of protecting groups for the hydroxyl group and the synthesis thereof may be found in "Protective Groups in Organic Synthesis" by T. W. Greene, John Wiley and Sons, 1981. The hydroxyl protecting group selected should be easily removed under conditions that are sufficiently mild, e.g., in 48% HF, acetonitrile, pyridine, or 0.5% HCl/water/ SUBSTITUTESHEET ethanol, and/or zinc, acetic acid so as not to disturb the ester linkage or other substituents of the taxol intermediate. However, Rg is preferably triethylsilyl, 1-ethoxyethyl or 2,2,2-trichloroethoxymethyl, and most preferably triethylsilyl. Also as noted previously, R 7 may be a sulfhydryl protecting group and R g may be an amine protecting group. Sulfhydryl protecting groups include hemithioacetals such as 1-ethoxyethyl and methoxymethyl, thioesters, or thiocarbonates. Amine protecting groups include carbamates, for example, 2,2,2-trichloroethylcarbamate or tertbutylcarbamate. A variety of sulfhydryl and amine protecting groups may be found in the above-identified text by T. W. Greene. Since β-lactam (2) has several asymmetric carbons, it is known to those skilled in the art that the compounds of the present invention having asymmetric carbon atoms may exist in diastereomeric, racemic, or optically active forms. All of these forms are contemplated within the scope of this invention. More specifically, the present invention includes enantiomers, diastereomers, racemic mixtures, and other mixtures thereof. β-lactam (2) can be prepared from readily available materials, as is illustrated in schemes A and B below: SUBSTITUTE SHEET Scheme A Scheme B reagents: (a) triethylamine, CH 2 Cl 2 ,. . 25°C, 18h; (b) 4 equiv eerie ammonium nitrate, CH 3 CN, -10°C, 10 min; (c) KOH, THF, H 2 0, 0°C, 30 min; (d) ethyl vinyl ether, THF, toluene sulfonic acid (cat.), 0°C, 1.5h; (e) n-butyllithium, ether, -78°C, 10 min; benzoyl chloride, -78°C, lh; (f) lithium diisopropyl amide, THF -78°C to -50°C; (g) lithium hexa- ethyldisilazide, THF -78°C to 0°C; (h) THF, -78°C to 25°C, 12h. SUBSTITUTESHEET The starting materials are readily available. In scheme A, α-acetoxy acetyl chloride is prepared from glycolic acid, and, in the presence of a tertiary amine, it cyclocondenses with imines prepared from aldehydes and p-methoxyaniline to give l-p-methoxyρhenyl-3-acyloxy-4- arylazetidin-2-ones. The p-methoxyphenyl group can be readily removed through oxidation with eerie ammonium nitrate, and the acyloxy group can be hydrolyzed under standard conditions familiar to those experienced in the art to provide 3-hydroxy-4-arylazetidin-2-ones. The 3-hydroxyl group is protected with 1-ethoxyethyl, but may be protected with variety of standard protecting groups such as the triethylsilyl group or other trialkyl (or aryl) silyl groups. In Scheme B, ethyl-α-triethylsilyloxyacetate is readily prepared from glycolic acid. The racemic β-lactams may be resolved into the pure enantiomers prior to protection by recrystallization of the corresponding 2-methoxy-2-(trifluoromethyl) phenylacetic esters. However, the reaction described hereinbelow in which the β-amido ester side chain is attached has the advantage of being highly diastereo¬ selective, thus permitting the use of a racemic mixture of side chain precursor. The 3-(l-ethoxyethoxy)-4-phenylazetidin-2-one of scheme A and the 3-(l-triethylsilyloxy)-4-phenylazetidin- 2-one of scheme B can be converted to β-lactam (2), by treatment with a base, preferably n-butyllithium, and an acyl chloride, alkylchloroformate, sulfonyl chloride, phosphinyl chloride or phosphoryl chloride at -78 °C or below. The process of the present invention is particularly useful for the esterification of mono- or polycyclic metal alkoxides which are represented by the formula SUBSTITUTESHEET in which E l E 2 and the carbon to which they are attached define a carbocyclic and/or heterocyclic skeleton which may be mono- or polycyclic and E 3 is hydrogen or hydrocarbon, preferably lower alkyl. Most preferably, the carbocyclic and/or heterocyclic skeleton comprises about 6 to 20 atoms and the hetero atoms are oxygen. The cyclic skeleton may be hydrocarbon and/or heterosubstituted with heterosubsti- tuents including, for example, esters, ethers, amines, alcohols, protected alcohols, carbonyl groups, halogens, oxygen, substituted oxygen or substituted nitrogen. When the metal alkoxides have the bi-, tri- or tetracyclic taxane nucleus, the process of the present invention may advantageously be used to prepare taxane derivatives, many of which have been found to have significant biological activity. As used herein, a metal alkoxide having the bicyclic taxane nucleus has the carbocyclic skeleton corresponding to rings A and B of metal alkoxide (3): SUBSTITUTESHEET M and i5 _ 27 are as previously defined. A metal alkoxide having the tricyclic taxane nucleus has the carbocyclic skeleton corresponding to rings A, B and C of metal alkoxide (3). A metal alkoxide having the tetracyclic taxane nucleus has carbocyclic rings A, B and C of metal alkoxide (3) and the oxetane ring defined by R 22 , K-23' and the carbons to which they are attached. Preferably, the metal alkoxide used in the process of the present invention is metal alkoxide (3). Most preferably, R 15 is -OT 2 or -OCOCH 3 ; R 16 is hydrogen; R 17 and R 18 together form an oxo; ^g is -OT 1 ; R 2Q and R 21 are hydrogen; R 22 and R 23 together with the carbons to which they are attached form an oxetane ring; R 24 is CH 3 COO-; R 25 is PhCOO-; R 26 is hydrogen; R 27 is hydroxy; and T± and T 2 are independently hydrogen or hydroxy protecting group. Metal substituent, M, of metal alkoxide (3) is a Group IA, IIA, IIIA, lanthanide or actinide element or a SUBSTITUTESHEET transition, Group IIIA, IVA, VA or VIA metal. Preferably, it is a Group IA, IIA or transition metal, and most preferably, it is lithium, magnesium, sodium, potassium or titantium. The metal alkoxide alkyl groups, either alone or with the various substituents defined hereinabove are preferably lower alkyl containing from one to six carbon atoms in the principal chain and up to 10 carbon atoms. They may be straight or branched chain and include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, aryl, hexyl, and the like. The metal alkoxide alkenyl groups, either alone or with the various substituents defined hereinabove are preferably lower alkenyl containing from two to six carbon atoms in the principal chain and up to 10 carbon atoms. They may be straight or branched chain and include ethenyl, propenyl, isopropenyl, butenyl, isobutenyl, aryl, hexenyl, and the like. The metal alkoxide alkynyl groups, either alone or with the various substituents defined hereinabove are preferably lower alkynyl containing from two to six carbon atoms in the principal chain and up to 10 carbon atoms. They may be straight or branched chain and include ethynyl, propynyl, butynyl, isobutynyl, aryl, hexynyl, and the like. Exemplary alkanoyloxy include acetate, propionate, butyrate, valerate, isobutyrate and the like. The more preferred alkanoyloxy is acetate. The metal alkoxide aryl moieties, either alone or with various substituents contain from 6 to 10 carbon atoms and include phenyl, α-naphthyl or β-naphthyl, etc. Substituents include alkanoxy, hydroxy, halogen, alkyl, aryl, alkenyl, acyl, acyloxy, nitro, amino, amido, etc. Phenyl is the more preferred aryl. SUBSTITUTESHEET Metal alkoxides (3) are prepared by reacting an alcohol having two to four rings of the taxane nucleus and a C-13 hydroxyl group with an organometallic compound in a suitable solvent. Preferably, the alcohol is a derivative of baccatin III or 10-deacetyl baccatin III having the structure wherein T-^ is a hydroxy protecting group, and Z is -OT 2 wherein T 2 is acyl, preferably acetyl, or other hydroxy protecting group. Most preferably, the alcohol is a protected baccatin III, in particular, 7-O-triethylsilyl baccatin III (which can be obtained as described by Greene, et al. in JACS 110, 5917 (1988) or by other routes) or 7,10-bis-O-triethylsilyl baccatin III. As reported in Greene et al., 10-deacetyl baccatin III is converted to 7-O-triethylsilyl-lO-deacetyl baccatin III according to the following reaction scheme: S U BSTIT (5) (6a) Under what is reported to be carefully optimized conditions, 10-deacetyl baccatin III is reacted with 20 equivalents of (C 2 H 5 ) 3 SiCl at 23°C under an argon atmosphere for 20 hours in the presence of 50 ml of pyridine/mmol of 10-deacetyl baccatin III to provide 7-triethylsilyl-10-deacetyl baccatin III (6a) as a reaction product in 84-86% yield after purification. The reaction product is then acetylated with 5 equivalents of CH 3 COCl and 25 mL of pyridine/mmol of (6a) at 0 °C under an argon atmosphere for 48 hours to provide 86% yield of 7-O-tri- ethylsilyl baccatin III (6b). Greene, et al. in JACS 110. 5917 at 5918 (1988) . Alternatively, 7-triethylsilyl-10-deacetyl baccatin III (6a) can be protected at C-10 oxygen with an acid labile hydroxyl protecting group. For example, treatment of (6a) with n-butyllithium in THF followed by triethylsilyl chloride (1.1 mol equiv.) at 0°C gives 7,10-bis-O-triethylsilyl baccatin IΪI (6c) in 95% yield. Also, (6a) can be converted to 7-O-triethylsilyl-10-(l- ethoxyethyl) baccatin III (6d) in 90% yield by treatment with excess ethyl vinyl ether and a catalytic amount of methane sulfonic acid. These preparations are illustrated in the reaction scheme below. SUBSTITUTESHEET 7-0-triethylsilyl baccatin III (6b) , 7 , 10-bis- O-triethylsilyl baccatin III (6c) , or 7-O-triethylsilyl- lθ-(l-ethoxyethyl) baccatin III (6d) is reacted with an organometallic compound such as n-butyllithium in a solvent such as tetrahydrofuran (THF) , to form the metal alkoxide 13-0-lithium-7-0-triethylsilyl baccatin III (7b) 13-O-lithium-7 , 10-bis-O-triethylsilyl baccatin III (7c) , or SUBSTITUTE SHEET 13-0-lithium-7-O-triethyIsily1-10-(1-ethoxyethyl) baccatin III (7d) as shown in the following reaction scheme: THF As illustrated in the following reaction scheme, a suitable metal alkoxide of the present invention such as 13-0-lithium-7-0-triethylsilyl baccatin III derivative (7b, 7c, or 7d) reacts with a β-lactam of the present invention to provide an intermediate (8b, 8c, or 8d) in which the C-7 hydroxyl group is protected with a triethylsilyl or 1-ethoxyethyl group. SUBSTITUTESHEET 7 b-d Intermediate compound (8b) readily converts to taxol when R-^ is -ORg, R 2 and R are hydrogen, I is phenyl, R 5 is benzoyl and Rg is a hydroxy protecting group such as triethylsilyl. Intermediate compound (8c) readily converts to taxotere when R-i is -OR. l 2 and R 3 are hydrogen, R 4 is phenyl, R 5 is tertbutoxycarbonyl and Rg is a hydroxy protecting group such as triethylsilyl. Intermediate compound (8d) readily converts to 10-deacetyl taxol when R-^ is -ORg, R 2 and R 3 are hydrogen, R 4 is phenyl, R5 is benzoyl, and Rg is a hydroxy protecting group such as triethylsilyl. Intermediate compounds (8b, 8c and 8d) may be converted to the indicated compounds by hydrolyzing the triethylsilyl and 1-ethoxyethyl groups under mild conditions so as not to disturb the ester linkage or the taxane derivative substituents. 8b TAXOL 8c TAXOTERE 8d 10-DEACETYL TAXOL Other taxane derivatives may readily be prepared by selection of the proper substituents R^ - R5 of β-lactam (2) or R 15 - R 7 of metal alkoxide (3). The preparation of such other compounds is illustrated in the examples which follow. Both the conversion of the alcohol to the metal alkoxide and the ultimate synthesis of the taxol can take place in the same reaction vessel. Preferably, the β-lactam is added to the reaction vessel after formation therein of the metal alkoxide. The organometallic compound n-butyllithium is preferably used to convert the alcohol to the corresponding metal alkoxide, but other sources of metallic substituent such as lithium diisopropyl amide, other lithium or magnesium amides, ethylmagnesium bromide, methylmagnesium bromide, other organolithium compounds, other organo agnesium compounds, organosodium, organotitanium, organozirconium, organozinc, organocadmium or organopotassium or the corresponding amides may also be used. Organometallic compounds are readily available, or may be prepared by available methods including reduction of organic halides with metal. Lower alkyl halides are preferred. For example, butyl bromide can be reacted with lithium metal in diethyl ether to give a solution of n-butyllithium in the following manner: -10°C CH 3 CH 2 CH 2 CH 2 Br + 2Li * ■ CH 3 CH 2 CH 2 CH 2 Li + LiBr Et-O Alternatively, the lithium alkoxide may be induced to undergo exchange with metal halides to form alkoxides of aluminum, boron, cerium, calcium, zirconium or zinc. SUBSTITUTESHEET Although THF is the preferred solvent for the reaction mixture, other ethereal solvents, such as dimethoxyethane, or aromatic solvents may also be suitable. Certain solvents, including some halogenated solvents and some straight-chain hydrocarbons in which the reactants are too poorly soluble, are not suitable. Other solvents are not appropriate for other reasons. For example, esters are not appropriate for use with certain organometallic compounds such as n-butyllithium due to incompatibility therewith. Although the reaction scheme disclosed herein is directed to the synthesis of certain taxol derivatives, it can be used with modifications in either the β-lactam or the tetracyclic metal alkoxide. Therefore metal alkoxides other than 13-0-lithium-7-0-triethylsilyl baccatin III may be used to form a taxol intermediate according to the method of this invention. The β-lactam and the tetracyclic metal alkoxide can be derived from natural or unnatural sources, to prepare other synthetic taxols, taxol derivatives, 10-deacetyltaxols, and the enantiomers and diastereomers thereof contemplated within the present invention. The process of the invention also has the important advantage of being highly diastereoselective. Therefore racemic mixtures of the side chain precursors may be used. Substantial cost savings may be realized because there is no need to resolve racemic β-lactams into their pure enantiomers. Additional cost savings may be realized because less side chain precursor, e.g., 60-70% less, is required relative to prior processes. The water solubility of compounds of formula (1) may be improved if R± is -ORg and R^ is -OT , and Rg and/or T-^ are a functional group which increases solubility, such as -COGCOR 1 wherein TITUTESHEET G is ethylene, propylene, CHCH, 1,2-cyclohexane, or 1,2-phenylene, R 1 = OH base, NR 2 R 3 , OR 3 , SR 3 , OCH 2 CONR 4 R 5 , OH R 2 = hydrogen, methyl R 3 = (CH 2 ) n NR 6 R 7 ; (CH 2 ) n N Θ R 6 R 7 R 8 X 1 Θ n = 1 to 3 R 4 = hydrogen, lower alkyl containing 1 to 4 carbons R 5 = hydrogen, lower alkyl containing 1 to 4 carbons, benzyl, hydroxyethyl, CH 2 C0 2 H, dimethylaminoethyl R°R' = lower alkyl containing 1 or 2 carbons, benzyl or R^ and R' together with the nitrogen atom of NR°R' form the following rings c-O Q OO CH, R 8 = lower alkyl containing 1 or 2 carbons, benzyl X T ® - halide base = NH 3 , (HOC 2 H 4 ) 3 N, N(CH 3 ) 3 , CH 3 N(C 2 H 4 OH) 2 , NH 2 (CH 2 ) 6 NH 2 , N-methylglucamine, NaOH, KOH. The preparation of compounds in which Rg or T-^ is -COGCOR 1 is set forth in Hangwitz U.S. Patent 4,942,184 which is incorporated herein by reference. The following examples illustrate the invention. SUBSTITUTESHEET EXAMPLE 1 Preparation of 2'-ethoxyethyl-7-triethylsilyl taxol, and subsequently taxol, from racemic β-lactam: To a solution of 7-triethylsilyl baccatin III (20mg, 0.028 mmol) in 1 ml of THF at -78°C was added dropwise 0.17 ml of a 0.164M solution of nBuLi in hexane. After 30 min at -78°C, a solution of cis-l-benzoyl-3- (l-ethoxyethoxy)-4-phenylazetidin-2-one (47.5 mg, 0.14 mmol) in 1 ml of THF was added dropwise to the mixture. The solution was allowed to slowly warm (over 1.5 h) to 0°C and was then stirred at 0°C for 1 h and 1 ml of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by flash chromatography to give 23 mg (80%) of (2*R, 3*S)-2'-ethoxyethyl-7-tri- ethylsilyl taxol and 3.5 mg (13%) of 2' ,3'-epi(2'S,. 3'R)-2'-ethoxyethyl-7-triethylsilyl taxol. A 5 mg sample of (2*R, 3'S)-2'-ethoxyethyl- 7-triethylsilyl taxol was dissolved in 2 ml of ethanol, and 0.5 ml of 0.5% aqueous HC1 solution was added. The mixture was stirred at 0°C for 30 h and diluted with 50 ml of ethyl acetate. The solution was extracted with 20 ml of saturated aqueous sodium bicarbonate solution, dried over sodium sulfate and concentrated. The residue was purified by flash chromatography to provide 4.5 mg (ca.90%) taxol, which was identical with an authentic sample in all respects. A 5 mg sample of 2' ,3'-epi(2'S,3'R)-2'-ethoxy- ethyl-7-triethylsilyl taxol was dissolved in 2 ml of ethanol and 0.5 ml of 0.5% aqueous HC1 solution was added. The mixture was stirred at 0°C for 30 h and diluted with 50 ml of ethyl acetate. The solution was extracted with 20 ml SUBSTITUTESHEET of saturated aqueous sodium bicarbonate solution, dried over sodium sulfate and concentrated. The residue was purified by flash chromatography to provide 4.5 mg (ca.90%) of 2' ,3'-eρitaxol. EXAMPLE 2 Preparation of 2' ,7-(bis)triethylsilyl taxol, and subsequently taxol, from racemic β-lactam: To a solution of 7-triethylsilyl baccatin III (lOOmg, 0.143 mmol) in 1 ml of THF at -45°C was added dropwise 0.087 ml of a 1.63M solution of nBuLi in hexane. After 1 h at -45°C, a solution of cis-l-benzoyl-3- . triethylsilyloxy)-4-phenylazetidin-2-one (274 mg, 0.715 mmol) in 1 ml of THF was added dropwise to the mixture. The solution was allowed to warm to 0°C and held at 0°C for 1 h. One ml of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by flash chromatography followed by recrystallization to give 131 mg (85%) of (2'R, 3 , S)-2' ,7-(bis)triethylsilyl taxol and 15 mg (10%) of 2' ,3 , -epi(2 , S,3'R)-2* ,7-(bis)triethylsilyl taxol. To a solution of 121.3 mg (0.112 mmol) of (2'R, 3'S)-2' ,7-(bis)triethylsilyl taxol in 6 ml of acetonitrile and 0.3 ml of pyridine at 0°C was added 0.9 ml of 48% aqueous HF. The mixture was stirred at 0°C for 8 h, then at 25°C for 6 h. The mixture was partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 113 mg of material which was purified by flash chromatography and recrystallization to give 94 mg (98%) taxol, which was identical with an authentic sample in all respects. SUBSTITUTESHEET To a solution of 5 mg of (2'R, 3'S)-2' ,7-(bis) triethylsilyl taxol in 0.5 ml of acetonitrile and 0.03 ml of pyridine at 0°C was added 0.09 ml of 48% aqueous HF. The mixture was stirred at 0°C for 8 h, then at 25°C for 6 h. The mixture was partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 5 mg of material which was purified by flash chromatography and recrystallization to give 4.6 mg (ca. 95%) of 2' ,3'-epitaxol. EXAMPLE 3 Preparation of 2' ,7-(bis)triethylsilyl taxol, and subsequently taxol, from optically active β-lactam: To a solution of 7-triethylsilyl baccatin III (100 mg, 0.143 mmol) in 1 ml of THF at -45°C was added dropwise 0.087 ml of a 1.63M solution of nBuLi in hexane. After 1 h at -45°C, a solution of (+)-cis-l-benzoyl-3- triethylsilyloxy-4-phenylazetidin-2-one (82 mg, 0.215 mmol) in 1 ml of THF was added dropwise to the mixture. The solution was allowed to warm to 0°C and held at 0°C for 2 hours. One ml of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by flash chromatography followed by recrystallization to give 145 mg (94%) of (2'R, 3'S)-2' ,7-(bis)triethylsilyl taxol. To a solution of 121.3 mg (0.112 mmol) of (2'R, 3*S)-2' ,7-(bis)triethylsilyl taxol in 6 ml of acetonitrile and 0.3 ml of pyridine at 0°C was added 0.9.ml of 48% aqueous HF. The mixture was stirred at 0°C for 8 h, then at 25°C for 6 h. The mixture was -partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 113 mg of SUBSTITUTE SHEET material which was purified by flash chromatography and recrystallization to give 94 mg (98%) taxol, which was identical with an authentic sample in all respects. EXAMPLE 4 Preparation of taxotere. To a solution of 7,10-bis-triethylsilyl baccatin III (200 mg, 0.248 mmol)) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-(tert- butoxycarbonyl)-3-triethylsilyloxy-4-phenylazetidin-2-one (467 mg, 1.24 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 280 mg of crude 2' ,7,10-tris-triethylsilyl taxotere. To a solution of 280 mg of the crude product obtained from the previous reaction in 12 mL of acetonitrile and 0.6 mL of pyridine at 0 °C was added 1.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 215 mg of material which was purified by flash chromatography to give 190 mg (95%) of taxotere, which was recrystallized from methanol/water. All analytical and spectral data were identical with that reported for taxotere in U.S. Patent 4,814,470. SUBSTITUTESHEET EXAMPLE 5 wherein N p2 is Preparation of 3'-desphenyl-3*-(2-naρhthyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3- triethylsilyloxy-4-(2-naphthyl)azetidin-2-one (620 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °-C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 320 mg of a mixture containing (2*R,3'S)-2* ,7-(bis)triethylsilyl-3'- desphenyl-3'-(2-naphthyl) taxol and a small amount of the (2'S,3 « R) isomer. SUBSTITUTESHEET To a solution of 320 mg (0.283 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 255 mg of material which was purified by flash chromatography to give 166 mg (64%) of 3'-desphenyl-3'-(2-naphthyl) taxol, which was recrystallized from methanol/water. m.p 164-165 °C; [α] 25 Na -52.6° (c 0.005, CHC1 3 ) . 1 H NMR (CDC1 3 , 300 MHz) S 8.14 (d, J = 7.3 Hz, 2H, benzoate ortho) , 7.96 ( , IH, aromatic), 7.90 (m, IH, aromatic), 7.85 (m, 2H, aromatic), 7.76 (m, 2H, aromatic), 7.60 (m, 3H, aromatic), 7.52 (m, 4H, aromatic), 7.41 (m, 2H, aromatic), 7.01 (d, J = 8.8 Hz, IH, NH) , 6.27 (s, IH, H10) , 6.26 (dd, J = 9.2, 9.2 Hz, IH, H13), 5.97 (dd, J = 8.8, 2.5 Hz, IH, H3'), 5.68 (d, J = 7.1 Hz, IH, H2β) , 4.93 (m, IH, H5), 4.92 (m, IH, H2*), 4.39 (m, IH, H7) , 4.30 (d, J - 8.5 Hz, IH, H20α), 4.20 (d, J = 8.5 Hz, IH, H20β) , 3.81 (d, J = 7.1 Hz, IH, H3), 3.60 (d, J = 5 Hz, IH, 2'OH), 2.48 (m, IH, H6 ), 2.45 (br, IH, 70H) , 2.39 (s, 3H, 4Ac) , 2.30 (m, 2H, H14), 2.24 (s, 3H, lOAc) , 1.83 (m, IH, H6β) - 1.82 (br s, 3H, Mel8), 1.68 (s, IH, 10H) , 1.68 (s, 3H, Mel9), 1.24 (s, 3H, Mel7), 1.14 (s, 3H, Mel6) . SUBSTITUTESHEET EXAMPLE 6 wherein N pl is Preparation of 3'-desphenyl-3*-(l-naphthyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(l-naρhthyl)azetidin-2-one (620 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 325 mg of a mixture containing (2"R,3'S)-2' ,7-(bis)triethylsilyl-3'- desphenyl-3'-(1-naphthyl) taxol and a small amount of the (2'S,3'R) isomer. SUBSTITUTESHEET To a solution of 325 mg (0.287 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 260 mg of material which was purified by flash chromatography to give 166 mg (64%) of 3 '-(1-naphthyl) taxol, which was recrystallized from methanol/water. m.p. 164-165 °C; [α] 25 Na -52.6° (c.0.005,- CHC1 3 ) . 1 H NMR (CDC1 3 , 300 MHz) 6 8.11 (d, J - 7.1 Hz, 2H, benzoate ortho), 8.11 (m, 3H, aromatic), 7.91 (m, 3H, aromatic), 7.70 (m, 2H, aromatic), 7.63-7.46 (m, 7H, aromatic), 6.75 (-, J _ 8.8 Hz, IH, NH), 6.52 (dd, J = 8.8, 1.6 Hz, IH, H3 1 ), 6.27 (s, IH, H10), 6.27 (dd, J = 9.1, 9.1 Hz, IH, H13), 5.68 (d, J = 7.1 Hz, IH, H2B) , 4.85 (dd, J - 7.6, 2.2 Hz, IH, H5), 4.97 (dd, J = 1.6 Hz, IH, H2 • ) , 4.39 (m, . IH, H7), 4.24 (d, J = 8.5 Hz, IH, H20α) , 4.17 (d, J = 8.5 Hz, IH, H20β), 3.80 (d, J = 7.1 Hz, IH, H3), 3.65 (br, IH, 2'OH), 2.55 (m, IH, H6α) , 2.48 (br, IH, 70H) , 2.41 (s, 3H, 4Ac), 2.38 (m, IH, H14), 1.96 (s, 3H, lOAc) , 1.86 (m, IH, H6β), 1.80 (br s, 3H, Mel8), 1.76 (s, IH, IOH) , 1.69 (s, 3H, Mel9), 1.28 (s, 3H, Mel7), 1.16 (s, 3H, Mel6). SUBSTITUTE SHEET EXAMPLE 7 Preparation of 3'-desphenyl-3'-(4-methoxyphenyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(4-methoxyphenyl)azetidin-2-one (590 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 320 mg of a mixture containing (2'R,3'S)-2' ,7-(bis)triethylsilyl-3'- desphenyl-3'-(4-methoxyphenyl) taxol and a small amount of the (2"S,3*R) isomer. To a solution of 320 mg (0.288 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 SUBSTITUTESHEET mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 255 mg of material which was purified by flash chromatography to give 172 mg (68%) of 3 '-desphenyl-3 '-(4-methoxyphenyl) taxol, which was recrystallized from ethanol/water. m p. 174-176 °C; [α] 25 Na -48.86° (c 0.05, CHC1 3 ) ^ • H NMR (CDC1 3 , 300 MHz) S 8.12 (d, J - 7.1 Hz, 2H, benzoate ortho), 7.72 (m, 2H, aromatic), 7.59 (m, IH, aromatic), 7.53-7.36 (m, 8H, aromatic), 6.96 (d, J = 8.8 Hz, IH, NH) , 6.90 (m, 2H, aromatic), 6.26 (s, IH, H10), 6.21 (dd, J = 9.3, 9.3 Hz, IH, H13), 5.70 (dd, J = 8.8, 2.7 Hz, IH, H3 ' ) , 5.66 (d, J = 6.8 Hz, IH, H2β) , 4.93 (dd, J = 9.9, 2.2 Hz, IH, H5), 4.74 (dd, J _ 5.5, 2.7 Hz, IH, H2 ' ) , 4.39 (m, IH, H7), 4.29 (d, J = 8.8 Hz, IH, H20 ) , 4.18 (d, J = 8.8.Hz, IH, H20B), 3.78 (d, J - 6.8 Hz, IH, H3), 3.78 (s, 3H, ArQMe), 3.67 (d, J = 5.5 Hz, IH, 2'OH), 2.61 (m, IH, H6α) , 2.50 (d, J = 4.4 Hz, IH, 70H) , 2.37 (s, 3H, 4Ac) , 2.31 (m, 211, H14), 2.22 (s, 3H, lOAc) , 1.84 (m, IH, H6β) , 1.79 (br s, 3H, Mel8), 1.79 (s, IH, lOH) , 1.67 (s, 3H, Mel9), 1.22 (s, 3H, Mel7), 1.13 (s, 3H, Mel6) . SUB S TITUTE SHEET EXAMPLE 8 Preparation of 3'-desphenyl-3'-(4-chlorophenyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(4-chlorophenyl)azetidin-2-one (595 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 320 mg of a mixture containing (2*R,3'S)-2' ,7-(bis)triethylsilyl 3'-desρhenyl-3'-(4-chlorophenyl) taxol and a small amount of the (2'S,3'R) isomer. To a solution of 320 mg (0.287 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. The mixture was stirred at 0 ° " C for SUBSTITUTESHEET 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 255 mg of material which was purified by flash chromatography to give 158 mg (62%) of 3 '-desphenyl-3 '-(4-chlorophenyl) taxol, which was recrystallized from methanol/water. m.p. 173-175 °C; [α] 25 Na -50.8° (c 0.01, CHC1 3 ). 1 H NMR (CDC1 3 , 300 MHz) S 8.13 (d, J = 7.1 Hz, 2H, benzoate ortho), 7.72 (d, J = 8.2 Hz, 2H, benzamide ortho) , 7.65-7.35 (m, 10H, aromatic), 6.97 (d, J = 8.8 Hz, IH, NH) , 6.27 (s, IH, H10), 6.25 (dd, J = 8.3, 8.3 Hz, IH, H13), 5.78 (dd, J = 8.8, 2.2 Hz, IH, H3 • ) , 5.67 (d, J = 7.1 Hz, IH, H2β), 4.95 (dd, J = 8.8, 2.2 Hz, IH, H5) , 4.77 (br s, IH, H2'), 4.40 (m, IH, H7) , 4.31 (d, J = 8.2 Hz, IH, H20α) , 4.19 (d, J = 8.2 Hz, IH, H20β) , 3.80 (d, J = 7.1 Hz, IH, H3) > 3.61 (br s, IH, 2'OH), 2.54 (m, IH, H6α) , 2.38 (s, 3H, 4Ac), 2.32 (m, 2H, H14), 2.24 (s, 3H, lOAc) , 1.85 (m, IH, H6β), 1.80 (br s, 3H, Mel8) , 1.68 (s, 3H, Mel9), 1.23 (s, 3H, Mel7), 1.14 (s, 3H, Mel6) . SUBSTITUTESHEET Preparation of 3'-desphenyl-3'-(4-bromophenyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution in nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(4-bromophenyl)azetidin-2-one (660 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture.. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 330 mg of a mixture containing (2"R,3'S)-2' ,7-(bis)triethylsilyl-3'- desρhenyl-3'-(4-bromophenyl) taxol and a small amount of the (2'S,3'R) isomer. To a solution of 330 mg (0.284 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. • The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between SUBS TITUTE S HEET saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 265 mg of material which was purified by flash chromatography to give 186 mg (64%) of 3'-desphenyl-3'-(4-bromophenyl) taxol, which was recrystallized from methanol/water. m 170-172 °C; [α] 25 Na -50.94° (c 0.01, CHC1 3 ) λ H NMR (CDC1 3 , 300 MHz) δ 8.12 (d, J = 7.2 Hz, 2H, benzoate ortho), 7.71 (m, 2H, aromatic), 7.61 (m, IH, aromatic), 7.50-7.47 (m, 6H, aromatic), 7.38 (m, 3H, aromatic), 7.04 (d, J = 8.8 Hz, IH, NH), 6.27 (s, IH, H10) , 6.23 (dd, J = 8.2, 8.2 Hz, IH, H13), 5.75 (dd, J - 8.8, 2.2 Hz, IH, H3') , 5.66 (d, J = 7.1 Hz, IH, H2β) , 4.94 (dd, J = 9.3, 1.7 Hz, IH, H5), 4.75 (dd, J a 2.2 Hz, IH, H2* ) , 4.38 (m, IH, H7) , 4.29 (d, J = 8.2 Hz, IH, H20α) , 4.18 (d, J = 8.2 Hz, IH, H20B), 3.79 (d, J = 7.1 Hz, IH, H3), 3.7 (br, IH, 2'OH), 2.53 (m, IH, H6α) , 2.38 (br, IH, 70H), 2.37 (s, 3H, 4Ac) , 2.30 (m, 2H, H14), 2.23 (s, 3H, lOAc) , 1.87 (m, IH, H6β) , 1.80 (br s, 3H, Melδ), 1.80 (s, IH, lOH) , 1.67 (s, 3H, Mel9), 1.22 (s, 3H, Mel7) , 1.13 (s, 3H, Mel6) . SUBSTITUTE SHEET EXAMPLE 10 Preparation of 3'-desphenyl-3'-(3,4-methylene- dioxyphenyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(3,4-methylenedioxyphenyl)azetidin-2-one (610 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 320 mg of a mixture containing (2'R,3'S)-2*,7-(bis) riethylsilyl-3'- desphenyl-3'-(3,4-methylenedioxyphenyl) taxol and a small amount of the (2*S,3*R) isomer. To a solution of 320 mg (0.284 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 SUBSTITUTE SHEET mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 113 mg of material which was purified by flash chromatography to give 165 mg (64%) of 3-desphenyl-3'-(3,4-methylenedioxyphenyl) taxol, which was recrystallized from methanol/water. m p. 178-180 °C;[α] 25 Na -46.6° (c 0.005, CHC1 3 ). ^ • H NMR (CDC1 3 , 300 MHz) S 8.14 (d, J = 7.2 Hz, 2H, benzoate ortho), 7.72 (m, 2H, aromatic), 7.15 (m, IH, aromatic), 7.50 (m, 2H, aromatic), 7.38 (m,2H, aromatic), 7.0 (m, IH, aromatic), 6.94 (m, 2H, aromatic), 6.88 (d, J = 9.1 Hz, IH, NH), 6.83 (m, IH, aromatic), 6.28 (s, IH, H10) , 6.23 (dd, J = 9.1, 9.1 Hz, IH, H13), 5.97 (s, 2H, methylene), 5.69 (dd, J = 9.1, 2.5 Hz, IH, H3') , 5.68 (d, J = 6.9 Hz, IH, H2β) , 4.95 (dd, J = 9.6, 2.2 Hz, IH, H5), 4.72 (dd, J = 2.5 Hz, IH, H2'), 4.41 (m, IH, H7), 4.31 (d, J = 8.4 Hz, IH, H20α) , 4.20 (d, J = 8.4 Hz, IH, H20β) , 3.81 (d, J = 6.9 Hz, IH, H3), 3.60 (br, IH, 2OH) , 2.56 (m, IH, H6α) , 2.43 (d, J = 4.1 Hz, IH, 70H) , 2.39 (s, 3H, 4Ac) , 2.31 (m, 2H, H14), 2.24 (s, 3H, lOAc), 1.88 (m, IH, H6B), 1.82 (br s, 3H, Mel8), 1.69 (s, IH, 10H), 1.68 (s, 3H, Mel9), 1.24 (s, 3H, Mel7), 1.15 (s, 3H, Mel6) . SUBSTITUTESHEET Preparation of 3'-desphenyl-3'-(3,4-dimethoxy- phenyl) taxo1. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(3,4-dimethoxyphenyl)azetidin-2-one (630 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 hr before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 330 mg of a mixture containing (2'R,3'S)-2' ,7-(bis)triethylsilyl-3'- desphenyl-3'-(3,4-dimethoxyphenyl) taxol and a small amount of the (2'S,3'R) isomer. To a solution of 330 mg (0.286 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 SUBSTITUTE SHEET mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 260 mg of material which was purified by flash chromatography to give 175 mg (67%) of 3'-desρhenyl-3 '-(3,4-dimethoxyphenyl) taxol, which was recrystallized from methanol/water. m .p. 165-167 °C; t ] 25 Na -42.0° (c 0.005, CHC1 3 ). 1 H NMR (CDC1 3 , 300 MHz) δ 8.12 (d, J = 8.3 Hz, 2H, benzoate ortho), 7.73 (d, J = 8.2 Hz, 2H, benzamide ortho), 7.65-7.35 (m, 6H, aromatic), 7.1-7.0 (m, 2H, aromatic), 6.94 (d, J - 8.8 Hz, IH, NH) , 6.88 (d, J = 8.3 Hz, 2H, aromatic), 6.27 (s, IH, H10), 6.21 (dd, J = 9.3, 9.3 Hz, IH, H13), 5.69 (m, 2H, H3 , H2β) , 4.94 (dd, Hz, J = 9.9, 2.2 Hz, IH, H5), 4.77 (d, J = 2.8 Hz, IH, H2 • ) , 4.39 (dd, J = 11.0, 6.6 Hz, IH, H7), 4.30 (d, J = 8.5 Hz, IH, H20α) , 4.19 (d, J = 8.5 Hz, IH, H20B), 3.88 (s, 3H, ArOMe) . 3.87 (s, 3H, ArOMe), 3.80 (d, J = 7.1 Hz, IH, H3), 3.59 (d, J = 4.4 Hz, IH, 2'OH), 2.54 (m, IH, H6α) , 2.38 (s, 3H, 4Ac) , 2.36 (m, 2H, H14α, H14B) , 2.23 (s, 3H, lOAc) , 1.86 (m, IH, H6β) , 1.80 (br s, 3H, Mel8), 1.68 (s, 3H, Mel9), 1.23 (s, 3H, Mel7), 1.14 (s, 3H, Mel6) . SUBSTITUTE SHEET EXAMPLE 12 Preparation of N-debenzoyl-N-ethoxycarbonyl taxol. To a solution of 7-triethylsilyl baccatin III (155 mg, 0.221 mmol) in 2 mL of THF at -45 °C was added dropwise 0.136 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-1-ethoxycarbonyl- 3-triethylsilyloxy-4-phenylazetidin-2-one (386 mg, 1.11 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 252 mg of a mixture containing (2*R,3'S)-2' ,7-(bis)triethylsilyl-N- debenzoyl-N-ethoxycarbonyl taxol and a small amount of the (2'S,3'R) isomer. To a solution of 252 mg (0.112 mmol) of the mixture obtained from the previous reaction in 12 mL of acetonitrile and 0.6 mL of pyridine at 0 °C was added 1.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. SUBSTITUTESHEET Evaporation of the ethyl acetate solution gave 216 mg of material which was purified by flash chromatography to give 155 mg (85%) of N-debenzoyl-N-ethoxycarbonyl taxol, which was recrystallized from methanol/water. m 161.5-162.5 °C; [α] 2° (c 0.51, CHC1 3 ) -H NMR (CDC1 3 , 300 MHz) δ 8.12 (d, J = 7.7 Hz, 2H, benzoate ortho), 7.65-7.3 (m, 8H, aromatic), 6.28 (m, IH, H10) 6.27(m, IH, H13), 5.67 (d, J = 7.1 Hz, IH, H2β), 5.53 (d, J = 9.3 Hz, IH, H3'), 5.29 (d, J = 9.3 Hz, IH, NH) , 4.94 (dd, J = 9.3, 2.2 Hz, IH, H5), 4.64 (dd, J = 5.0, 2.8 Hz, IH, H2'), 4.41 (m, IH, H7) , 4.29 (d, J = 8.5 Hz, IH, H20α) , 4.17 (d, J = 8.5 Hz, IH, H20B) , 4.01 (q, J = 7.1 Hz, 2H, COOCH 2 CH 3 ), 3.79 (d, J = 7.1 Hz, IH, H3), 3.45 (d, J = 5 Hz, IH, 2'OH), 2.54 (m, IH, H6α) , 2.47 (d, J = 3.9 Hz IH, 70H) , 2.36 (s, 3H, 4Ac),2.24 (s, 3H, lOAc) , 2.22 (m, 2H, H14α, H14β), 1.87 (m, IH, H6α) , 1.83 (br S, 3H, Mel8), 1.77 (s, IH, 10H), 1.68 (s, 3H, Mel9), 1.27 (s, 3H, Mel7) , 1.15 (s, 3H, Mel6), 1.14 (t, J = 7.1 Hz, 2H, COOCH CH3) . SUBSTITUTESHEET EXAMPLE 13 Preparation of 3'-desphenyl-3'-(4-nitrophenyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(4-nitrophenyl)azetidin-2-one (610 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 320 mg of a mixture containing (2'R,3'S)-2' ,7-(bis)triethylsilyl-3'- desphenyl-3'-(4-nitrophenyl) taxol and a small amount of the (2'S,3*R) isomer. To a solution of 320 mg (0.284 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 SUBSTITUTESHEET mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 255 mg of material which was purified by flash chromatography to give 147 mg (57%) of 3'-desphenyl-3'-(4-nitrophenyl) taxol, which was recrystallized from methanol/water. m.p. 188-190 °C; [α] 25 Na -63.7° (c 0.01, CHC1 3 ). λ H NMR (CDC1 3 , 300 MHz) δ Ω 8.26 (d, J = 8.8 Hz, 2H, benzoate ortho), 8.20 (m, 2H, aromatic), 7.73 (m, 4H, aromatic), 7.60 (m, IH, aromatic), 7.52 (m, 4H, aromatic), 7.41 (m, IH, aromatic), 7.15 (d, J = 8.8 Hz, IH, NH) , 6.26 (s, IH, H10), 6.26 (dd, J = 9.3, 9.3 Hz, IH, H13), 5.93 (dd, J = 8.8, 2.8 Hz, IH, H3* ) , 5.66 (d, J = 6.6 Hz, IH, H2β) , 4.94 (dd, J = 9.3, 1.7 Hz, IH, H5) , 4.82 (dd, J = 3.9, 2.8 Hz, IH, H2'), 4.38 (m, IH, H7) , 4.30 (d, J = 8.8 Hz, IH, H20α) , 4.19 (d, J = 8.8 Hz, IH, H20β) , 3.86 (d, J = 3.9 Hz, IH, 2'OH), 3.79 (d, J = 6.6 Hz, IH, H3), 2.55 (m, IH, H6 ) , 2.46 (d, J = 3.8 Hz, IH, 70H) , 2.41 (s, 3H, 4Ac) , 2.38 (m, 2H, H14), 2.23 (s, 3H, lOAc) , 1.82 (m, IH, H6β) , 1.80 (br . s, 3H, MelB), 1.74 (s, IH, lOH) , 1.68 (s, 3H, Mel9), 1.21 (s, 3H, Mel7), 1.13 (s, 3H, Mel6) . SUBSTITUTESHEET EXAMPLE 14 Preparation of 3'-desphenyl-3'-(2-furyl) taxol. To a solution of 7-triethylsilyl baccatin III (100 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.087 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(2-furyl)azetidin-2-one (266 mg, 0.715 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 143 mg of a mixture containing (2'R,3*S)-2' ,7-(bis)triethylsilyl- 3'-desphenyl-3'-(2-furyl) taxol and a small amount of the (2*S,3*R) isomer. To a solution of 143 mg of the mixture obtained from the previous reaction in 6 mL of acetonitrile and 0.3 mL of pyridine at 0 °C was added 0.9 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for SUBSTITUTESHEET 13 h, and partitioned between saturated aqueous bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 115 mg of material which was purified by flash chromatography to give 98 mg (81%) of 3'-desphenyl- 3'-(2-furyl) taxol, which was recrystallized from methanol/water. m .p. 174-176 °C;[α] 25 Na -47.8° (c 0.045, CHC1 3 ) 1 H NMR (CDC1 3 , 300 MHz) δ 8.14 (d, J = 7.0 Hz, 2H, benzoate ortho), 7.74 (m, 2H, aromatic), 7.51 (m, 7H, aromatic), 6.86 (d, J = 9.2 Hz, IH, NH) , 6.40 (d, J = 1.2 Hz, 2H, furyl), 6.29 (s, IH, H10), 6.24 (dd, J = 9.2, 9.2 Hz, -IH, H13), 5.89 (dd, J = 9.2, 2.4 Hz, IH, H3' ) , 5.69 (d, J = 7.0 Hz, IH, H2β), 4.96 (dd, J = 9.5, 1.8 Hz, IH, H5) , 4.83 (d, J = 2.4 Hz, IH, H2'), 4.42 (dd, J = 10.7, 6.7 Hz, IH, H7) , 4.31 (d, J = 8.6 Hz, IH, H20α) , 4.20 (d, J = 8.6 Hz, IH, H20β), 3.83 (d, J = 7.0 Hz, IH, H3), 2.56 (m, IH, H6α) , 2.43 (s, 3H, 4Ac), 2.35 (m, 2H, H14), 2.24 (s, 3H, lOAc) , 1.89 (m, IH, H6β), 1.87 (br s, 3H, Mel8), 1.87 (s, IH, 10H), 1.69 (s, 3H, Mel9), 1.25 (s, 3H, Mel7) , 1.15 (s, 3H, Mel6). SUBSTITUTESHEET EXAMPLE 15 Preparation of 3'-desρhenyl-3*-(4-fluorophenyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-benzoyl-3-tri- ethylsilyloxy-4-(4-fluorophenyl)azetidin-2-one (570 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 315 mg of a mixture containing (2'R,3'S)-2' ,7-(bis)triethylsilyl-3'- desphenyl-3'-(4-fluorophenyl) taxol and a small amount of the (2'S,3'R) isomer. To a solution of 315 mg (0.286 mmol) of the mixture obtained from the previous reaction in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 SUB S TITUTE SHE mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 250 mg of material which was purified by flash chromatography to give 160 mg (64%) of 3 '-desphenyl-3 '-(4-fluorophenyl) taxol, which was recrystallized from methanol/water. m.p.171-173 °C; [α] 25 Na -49.0° (c 0.005, CHC1 3 ). 1 H NMR (CDC1 3 , 300 MHz) δ 8.13 (d, J = 7.5 Hz, 2H, benzoate ortho), 7.25 (m, 2H, aromatic), 7.61 (m, IH, aromatic), 7.50 (m, 4H, aromatic), 7.43 (m, 2H, aromatic), 7.10 (m, 2H, aromatic), 6.96 (d, J = 8.7 Hz, IH, NH) , 6.27 (s, IH, H10), 6.25 (dd, J = 8.7, 8.7 Hz, IH, H13), 5.79 (dd, J = 8.7, 2.4 Hz, IH, H3 ' ) , 5.67 (d, J = 7.1 Hz, IH, H2B) , 4.45 (dd, J - 7.9 Hz, IH, H5), 4.76 (dd, J = 4.8, 2.4 Hz, IH, H2'), 4.39 (m, IH, H7) , 4.31 (d, J = 8.9 Hz, IH, H20α) - 4.20 (d, J = 8.9 Hz, IH, H20B) , 3.80 (d, J = 7.1 Hz, IH, H3), 3.57 (d, J = 4.8 Hz, IH, 2'OH), 2.58 (m, IH, H6a) , 2.43 (d, J = 4.3 Hz, IH, 70H) , 2.38 (s, 3H, 4Ac) , 2.30 (m, 2H, H14), 2.24 (s, 3H, lOAc) , 1.85 (m, IH, H6β) , 1.80 (br s, 3H, Mel8), 1.69 (s, IH, 1OH) , 1.55 (s, 3H, Mel9), 1.23 (s, 3H, Mel7), 1.14 (s, 3H, Mel6) . SUBSTITUTESHEET EXAMPLE 16 Preparation of 3 '-Desphenyl-3'-(2-thienyl) taxol. To a solution of 7-triethylsilyl baccatin III (100 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.087 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-(4-benzoyl)-3- triethylsilyloxy-4-(2-thienyl)azetidin-2-one (277 mg, 0.715 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 169 mg of a mixture containing (2'R,3*S)-2' ,7-(bis)triethylsilyl- 3'-des henyl-3'-(2-thienyl) taxol and a small amount of the (2'S,3'R) isomer. To a solution of 169 mg of the mixture obtained from the previous reaction in 6 mL of acetonitrile and 0.3 mL of pyridine at 0 °C was added 0.9 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for SUB S TITUTESHEET 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 140 mg of material which was purified by flash chromatography to give 93 mg (76%) of 3 '-desphenyl- 3'-(2-thienyl) taxol, which was recrystallized from methanol/water. m p. 173-175 °C; [α] 25 N --42.1° (c 0.515, CHCl ) 1 H NMR (CDC1 3 , 300 MHz) δ 8.14 (d, J = 7.1 Hz, 2H, benzoate ortho), 7.72 (d, J = 8.7 Hz, 2H, benzamide ortho), 7.65-7.35 (m, 6H, aromatic), 7.31 (dd, J = 5.5, 1.1 Hz, IH, thienyl), 7.19 (dd, J =3.9, 1.1 Hz, IH, thienyl), 7.03 (dd, J - 5.5, 3.9 Hz, IH, thienyl), 6.96 (d, J = 8.8 Hz, IH, NH), 6.28 (s, IH, H10), 6.24 (dd, J = 8.8, 7.7 Hz, IH, H13), 6.05 (dd, J = 8.8, 1.7 Hz, IH, H3' ) , 5.68 (d, J = 7.1 Hz, IH, H2), 4.95 (dd, J = 9.3, 1.7 Hz, IH, H5) , 4.78 (d, J = 2.2 Hz, IH, H2'), 4.40 (dd, J = 11.0, 6.6 Hz, IH, H7) , 4.31 (d, J = 8.5 Hz, IH, H20α) , 4.20 (d, J = 8.5 Hz, IH, H20B), 3.81 (d, J = 7.1 Hz, IH, H3), 3.72 (br. s, IH, 2'OH), 2.54 (m, IH, H6α) , 2.41 (s, 3H, 4Ac) , 2.37 (m, 2H, H14α, H14β), 2.23 (s, 3H, lOAc) , 1.88 (m, IH, H6α) , 1.82 (br s, 3H, Mel8), 1.68 (s, 3H, Mel9), 1.23 (s, 3H, Mel7) , 1.14 (s, 3H, Mel6). SUBSTITUTE SHEET EXAMPLE 17 Preparation of 2' ,7-hydroxy protected Taxol using magnesium alkoxide: To a solution of 7-triethylsilyl baccatin III (100 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.048 mL of a 3.0 M solution of methyl magnesium bromide in ether. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-triethylsilyloxy-4-phenylazetidin-2-one (82 mg, 0.215 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 4 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by flash chromatography followed by recrystalli¬ zation to give 148 mg (96%) of (2'R,3 • S)-2',7-(bis)tri¬ ethylsilyl taxol. EXAMPLE 18 Preparation of 2',7-hydroxy protected Taxol using potassium alkoxide: To a solution of 7-triethylsilyl baccatin III (100 mg, 0.143 mmol) in 1 mL of THF at -45°C was added dropwise 0.286 mL of a 0.5 M solution of potassium hexamethyldisilazide in toluene. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-triethylsilyloxy-4-phenyl- azetidin-2-one (82 mg, 0.215 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0°C and kept at that temperature for 3 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer S UB S T IT UTE S HEET gave a residue which was purified by flash chromatography followed by recrystallization to give 139 mg (90%) of (2^,3*8)-2' ,7-(bis)triethylsilyl taxol. EXAMPLE 19 Preparation of 2',7-hydroxy protected Taxol using lithium alkoxide from lithium hexamethyldisilazide: To a solution of 7-triethylsilyl baccatin III (100 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.143 mL of a 1.0 M solution of lithium hexa- methyldisilazide in THF. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-triethylsilyloxy-4-phenylazetidin- 2-one (82 mg, 0.215 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0°C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by flash chromatography followed by recrystalli¬ zation to give 151 mg (98%) of (2'R,3'S)-2' ,7-(bis)tri- ethylsilyl taxol. EXAMPLE 20 Preparation of Taxol using lithium alkoxide (from lithium hexamethyldisilazide) : To a solution of 7-triethylsilyl baccatin III (100 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.143 mL of a 1.0 M solution of lithium hexa¬ methyldisilazide in THF. After 1 h at. -45 °C, a solution of (+)-cis-l-benzoyl-3- (2-methoxy-2-propyloxy)-4-phenyl- azetidin-2-one (58 mg, 0.172 mmol) in 1 mL of THF was added dropwise. to the mixture. The solution was warmed to 0°C SUBSTITUTESHEET and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by recrystallization to give 147 mg (99%) of (2'R,3'S)-2'-(2-methoxy-2-propyloxy)- 7-triethylsilyl taxol. To a solution of 116 mg (0.112 mmol) of (2'R,3*S)-2*-(2-methoxy-2-propyloxy)-7-triethylsilyl taxol in 6 mL of acetonitrile and 0.3 mL of pyridine at 0°C was added 0.9 mL of 48% aqueous HF. The mixture was stirred at 0°C for 8 h, then at 25°C for 10 h. The mixture was partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 113 mg of material which, was purified by recrystallization to give 95 mg (99%) of taxol, which was identical with an authentic sample.in all respects. EXAMPLE 21 Menthyl N-benzoyl-(2'R,3'S)-phenylisoserine ester. To a solution of (-) -menthol (22 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.143 . mL of a 1.0 M solution of lithium hexamethyldisilazide in THF. After 1 h at -45 °C, a solution of (+) -cis-l-benzoyl-3-(2-methoxy-2- propyloxy)-4-phenylazetidin-2-one (58 mg, 0.172 mmol) in 1 SUBSTITUTE SHEET L of THF was added dropwise to the mixture. The solution was warmed to 0°C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave 77 mg of a residue which was dissolved in 6 mL of THF at 0°C. To this solution was added 0.9 mL of glacial acetic acid and .9 L of water. The mixture was stirred at 0°C for 3 h, then partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 70 mg of material which was purified by chromatography on silica gel to give 48 mg (80%) of methyl N-benzoyl-(2'R,3'S)-phenylisoserine ester. EXAMPLE 22 Bornyl N-benzoyl-(2'R,3'S)-phenylisoserine ester. To a solution of (-)-borneol (22 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.143 mL of a 1.0 M solution of lithium hexamethyldisilazide in THF. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-(2-methoxy-2- propyloxy)-4-phenylazetidin-2-one (58 mg, 0.172 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0°C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the SUBSTITUTESHEET organic layer gave 75 mg of a residue which was dissolved in 6 mL of THF at 0°C. To this solution was added 0.9 mL of glacial acetic acid and .9 mL of water. The mixture was stirred at 0°C for 3 h, then partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 70 mg of material which was purified by chromatography on silica gel to give 54 mg (90%) of bornyl N-benzoyl-(2'R,3'S)-phenylisoserine ester. EXAMPLE 23 S-verbenyl N-benzoyl-(2*R,3'S)-phenylisoserine ester. To a solution of S-cis-verbenol (22 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.143 mL of a 1.0 M solution of lithium hexamethyldisilazide in THF. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-(2-methoxy-2- propyloxy)-4-phenylazetidin-2-one (58 mg, 0.172 mmol) in 1 mL of THF was added dropwise to the mixture. The solution . was warmed to 0°C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave 79 mg of a residue with was dissolved in 6 mL of THF at 0°C. To this solution was added 0.9 mL of glacial acetic acid and .9 mL of water. The mixture was stirred at 0°C for 3 h, then partitioned between saturated SU B S T IT UTE S HEET aqueous sodium bicarbonate and ehtyl acetate. Evaporation of the ethyl acetate solution gave 70 mg of material which was purified by chromatography on silica gel to give 55 mg (92%) of S-verbenyl N-benzoyl-(2'R,3'S)-phenylisoserine ester. EXAMPLE 24 Terpinen-4-yl N-benzoyl-(2'R,3'S)-phenylisoserine ester. To a solution of (+)-terpinene-4-ol (22 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.143 mL of a 1.0 M solution of lithium hexamethyldisilazide in THF. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-(2-methoxy- 2-propyloxy)-4-phenylazetidin-2-one (58 mg, 0.172 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0°C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave 80 mg of a residue which was dissolved in 6 mL of THF at 0°C for 3 h, then partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 70 mg of material which was purified by chromatography on silica gel to give 50 mg (83%) of terpinen-4-yl N-benzoyl- (2*R,3'S)-phenylisoserine ester. S UBSTITUTESHEET EXAMPLE 25 Isopinocamphenyl N-benzoyl-(2 • R,3'S)-phenyl- isoserine ester. To a solution of (-)-isopinocamphenyl (22 mg, 0.143 mmol) in 1 mL of. THF at -45 °C was added dropwise 0.143 mL of a 1.0 M solution of lithium hexamethyldisilazide in THF. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-(2- methoxy-2-propyloxy)-4-phenylazetidin-2-one (58 mg, 0.172 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0°C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave 77 mg of a residue which was dissolved in 6 mL of THF at 0°C. To this solution was added 0.9 mL of glacial acetic acid and .9 mL of water. The mixture was stirred at 0°C for 3 h, then partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 70 mg of material which was purified by chromatography on silica gel to give 53 mg (89%) of isocamphenyl N-benzoyl- (2'R,3'S)-phenylisoserine ester. SUBSTITUTE S HEET EXAMPLE 26 α-terpineyl N-benzoyl-(2'R^.'Sj-phenylisoserine ester. To a solution of (-)-menthol (22 mg, 0.143 mmol) in 1 mL of THF at -45 °C was added dropwise 0.143 mL of a 1.0 M solution of lithium hexamethyldisilazide in THF. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-(2-methoxy-2- propyloxy)-4-phenylazetidin-2-one (58 mg, 0.172 mmol) in 1 mL of THF was added dropwise to the mixture. The solution was warmed to 0°C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave 73 mg of a residue which was dissolved in 6 mL of THF at 0°C. To this solution was added 0.9 mL of glacial acetic acid and .9 mL of water. The mixture was stirred at 0°C for 3 h, then partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 70 mg of material which was purified by chromatography on silica gel to give 48 mg (80%) of α-terpineyl N-benzoyl-(2*R,3'S)-phenylisoserine ester. SUBSTITUTESHEET EXAMPLE 27 Preparation of 2',7-hydroxy protected Taxol using sodium alkoxide: To a solution of 7-triethylsilyl baccatin III (100 mg, 0.143 mmol) in 1 mL of THF at -45°C is added dropwise 0.143 mL of a 1 M solution of sodium hexamethyl-- disilazide in THF. After 1 h at -45 °C, a solution of (+)-cis-l-benzoyl-3-triethylsilyloxy-4-phenylazetidin-2-one (82 mg, 0.215 mmol) in 1 mL of THF is added dropwise to the mixture. The solution is warmed to 0°C and kept at that temperature for 3 h before 1 mL of a 10% solution of AcOH in THF is added. The mixture is partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gives a residue which is purified by flash chromatography followed by recrystalli¬ zation to give 108 mg (70%) of (2*R,3*S)-2 • ,7-(bis)tri- ethylsilyl taxol. SUBSTITUTESHEET EXAMPLE 28 Preparation of N-debenzoyl-N- ( 4-chlorobenzoyl ) taxol To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of (+)-cis-l-(4-chloro- benzoyl)-3-triethylsilyloxy-4-phenylazetidin-2-one (215 mg, 0.515 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 320 mg of crude (2'R,3'S)-2' ,7-(bis)triethylsilyl-N-debenzoyl-N-(4- chlorobenzoyl) taxol. SUBSTITUTESHEET To a solution of 320 mg (0.286 mmol) of this crude product in 18 mL of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 252 mg of material which was purified by flash chromatography to give 213 mg (84%) of N-debenzoyl- N-(4-chlorobenzoyl) taxol, which was recrystallized from methanol/water. m .p. 179-181 °C; [α]ι25 D Na -49.8° (c 0.01, CHC1 3 ) X H NMR (CDC1 3 , 300 MHz) δ 8.12 (d, J = 7.1 Hz, 2H, benzoate ortho), 7.64 (m, 2H, aromatic), 7.60 (m, IH, aromatic), 7.49 (m, 9H, aromatic), 7.03 (d, J ■ 8.8 Hz, IH, NH), 6.26 (s, IH, H10), 6.21 (dd, J = 8.2, 8.2 Hz, IH, H13), 5.76 (dd, J = 8.8, 2.2 Hz, IH, H3*) , 5.66 (d, J = 7.1 Hz, IH, H2β), 4.92 (dd, J = 9.9, 1.1 Hz, IH, H5) , 4.77 (dd, J = 5.5, 2.2 Hz, IH, H2'), 4.38 (m, IH, H7), 4.29 (d, J = 8.8 Hz, IH, H20α), 4.18 (d, J = 8.5 Hz, IH, H20B), 3.78 (d, J = 6.6 Hz, IH, H3), 3.35 (d, J = 5.5 Hz, IH, 2'OH), 2.55 (m, IH, H6α), 2.49 (d, J = 4.2 Hz, IH, 70H) , 2.36 (s, 3H, 4Ac) , 2.28 (m, 2H, H14), 2.22 (s, 3H, lOAc) , 1.85 (m, IH, H6β) , 1.77 (br s, 3H, Mel8) , 1.76 (s, IH, lOH) , 1.67 (s, 3H, Mel9), 1.22 (s, 3H, Mel7), 1.13 (s, 3H, Mel6) . EXAMPLE 29 Preparation of N-debenzoyl-N- ( 4-t-butylbenzoyl ) taxol To a solution of 7-triethylsilyl baccatin III (200 mg, 0.286 mmol) in 2 mL of THF at -45 °C was added dropwise 0.174 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of (+)-cis-l-(4-t-butyl- benzoyl)-3-triethylsilyloxy-4-phenylazetidin-2-one (226 mg, 0.515 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 2 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 330 mg of crude (2'R,3'S)-2' ,7-(bis)triethylsilyl-N-debenzoyl-N-(4- t-butylbenzoyl) taxol. To a solution of 330 mg (0.289 mmol) of this crude product in 18 L of acetonitrile and 0.93 mL of pyridine at 0 °C was added 2.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl SUBSTITUTE SHEET acetate solution gave 260 mg of material which was purified by flash chromatography to give 240 mg (92%) of N-debenzoyl- N-(4-t-butylbenzoyl) taxol, which was recrystallized from methanol/water. m.p. 171-173 °C; [α] 25 Na -49.1° (c 0.05, CHC1 3 ) . λ H NMR (CDC1 3 , 300 MHz) δ 8.13 (d, J = 7.1 Hz, 2H, benzoate ortho), 7.76-7.25 (m, 12H, aromatic), 6.98 (d, J = 8.8 Hz, IH, NH), 6.27 (s, IH, H10), 6.21 (dd, J = 8.8, 8.8 Hz, IH, H13), 5.77 (dd, J = 8.8, 2.7 Hz, IH, H3') , 5.67 (d, J = 6.6 Hz, IH, II2β), 4.94 (dd, J = 9.3, 1.2 Hz, IH, H5) , 4.78 (dd, J = 4.4, 2.7 Hz, IH, H2') , 4.38 (m, IH, H7), 4.29 (d, J = 8.2 Hz, IH, H20α), 4.20 (d, J = 8.2 Hz, IH, H20B) , 3.79 (d, J = 6.6 Hz, IH, H3), 3.65 (d, J = 4.4 Hz, IH, 2'OH), 2.57 (m, IH, H6α), 2.48 (d, J = 4.1 Hz, IH, 70H) , 2.37 (s, 3H, 4AC) , 2.31 (m, 2H, H14) , 2.22 (s , 3H, lOAc) , 1. 85 (m, IH, H6β) , 1. 79 (br s , 3H - Mel8) , 1. 68 (s , IH, lOH) , 1. 68 (s , 3H, Mel9 ) , 1.29 (s , 9H, Ar fc Bιι) , 1.23 (s , 3H, Mel7) , 1.13 (s , 3H, Mel6) . EXAMPLE 30 Preparation of N-debenzoyl-N-(4-methoxybenzoyl)- 3'-desphenyl-3'-(4-fluorophenyl) taxol. To a solution of 7-triethylsilyl baccatin III (200 mg, 0.285 mmol) in 2 mL of THF at -45 °C was added dropwise 0.175 mL of a 1.63M solution of nBuLi in hexane. After 0.5 h at -45 °C, a solution of cis-l-(4-methoxy- benzoyl)-3-triethyIsilyloxy-4-(4-fluorophenyl)azetidin- 2-one (614 mg, 1.43 mmol) in 2 mL of THF was added dropwise to the mixture. The solution was warmed to 0 °C and kept at that temperature for 1 h before 1 mL of a 10% solution of AcOH in THF was added. The mixture was partitioned between saturated aqueous NaHC0 3 and 60/40 ethyl acetate/hexane. Evaporation of the organic layer gave a residue which was purified by filtration through silica gel to give 362 mg of a mixture containing (2'R,3 'S)-2' ,7- (bis)triethylsilyl-N-debenzoyl-N-(4-methoxybenzoyl)-3'- desphenyl-3*-(4-fluorophenyl) taxol and a small amount of the (2'S,3'R) isomer. SUBSTITUTE SHEET To a solution of 362 mg of the mixture obtained from the previous reaction in 12 mL of acetonitrile and 0.6 mL of pyridine at 0 °C was added 1.8 mL of 48% aqueous HF. The mixture was stirred at 0 °C for 3 h, then at 25 °C for 13 h, and partitioned between saturated aqueous sodium bicarbonate and ethyl acetate. Evaporation of the ethyl acetate solution gave 269 mg of material which was purified by flash chromatography to give 183 mg (71%) of N-debenzoyl- N-(4-methoxybenzoyl)-3'-desphenyl-3'-(4-fluorophenyl) taxol, which was recrystallized from methanol/water. m .p. 172.5-174.5 °C; [α] 25 Na -47.0° (c 0.0044, CHC1 3 ). λ H NMR (CDC1 3 , 300 MHz) δ 8.13 (d, J = 7.2 Hz, 2H, benzoate ortho), 7.7-7.4 (m, 9H, aromatic), 7.10 (dd, J = 8.8, 8.8 Hz, 2H, aromatic), 6.97 (d, J = 8.8 Hz, IH, NH) , 6.27 (s, IH, H10), 6.23 (dd, J = 8.8, 8.8 Hz, IH, H13), 5.76 (dd, J = 8.8, 2.2 Hz, IH, H3') , 5.67 (d, J = 7.1 Hz, IH, H2β), 4.94 (dd, J = 9.9, 2.2 Hz, IH, H5), 4.75 (dd, J = 4.4, 2.2 Hz, IH, H2'), 4.39 (m, IH, H7) , 4.31 (d, J = 8.5 Hz, IH, H20α), 4.19 (d, J = 8.5 Hz, IH, H20B), 3.79 (d, J = 7.1 Hz, IH, H3), 3.59 (d, J = 4.4 Hz, IH, 2'OH), 2.54 (m, IH, H6α), 2.47 (d, J = 4.4 Hz, IH, 70H) , 2.36 (s, 3H, 4Ac) , 2.30 (m, 2H, H14cc, H14β), 2.24 (s, 3H, lOAc), 1.88 (m, IH, H6α), 1.78 (br s, 3H, Mel8) . 1.74 (s, .IH, lOH), 1.68 (s, 3H, Mel9), 1.23 (s, 3H, Mel7) , 1.14 (s, 3H, Mel6) . In view of the above, it will be seen that the several objects of the invention are achieved. As various changes could be made in the above compositions and processes without departing from the scope of the invention, it is intended that all matter contained in the above description be interpreted as illustrative and not in a limiting sense. SUBSTITUTESHEET

Claims: WHAT I CLAIM IS: 1. A process for the preparation of a substituted isoserine ester having the formula comprising reacting a β-lactam with a metal alkoxide, the β-lactam having the formula and the metal alkoxide having the formula MOCE 1 E 2 E 3 wherein R j L is -ORg, -SR 7 , or -NRgRg; R 2 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; R 3 and R 4 are independently hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, or acyl, provided, however, that R 3 and R 4 are not both acyl; R 5 is -COR 1Q , -COOR 10 , -COSR 10 ' -CONRgR 10 , -S0 2 R 11 , or -POR 12 R 13 , Rg is hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, hydroxy protecting group, or a functional group which increases the water solubility of the taxane derivative. SUBSTITUTESHEET R 7 is alkyl, alkenyl, alkynyl, aryl, heteroaryl, or sulfhydryl protecting group, Rg is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; Rg is an amino protecting group; R 10 is alkyl, alkenyl, alkynyl, aryl, or heteroaryl, R lχ is alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR 10 , or -NR 8 R 14 , R-^ 2 and R 13 are independently alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR 10 , or -NRgR 14 , R 14 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; and E- j^ , E 2 and E 3 are independently hydrogen, hydrocarbon or cyclic, provided, at least one of E , E 2 and E 3 is other than hydrogen. 2. A process as set froth in claim 1 wherein the carbon to which E , E 2 and E 3 are attached is a secondary or tertiary carbon. 3. A process as set forth in claim 1 wherein at least one of E lΛ E 2 and E 3 comprises a carbocyclic skeleton. 4. A process as set forth in claim 1 wherein two of E r E 2 and E 3 together with the carbon to which they are attached comprise a polycyclic skeleton. 5. A process as set forth in claim 1 wherein two of E j _ , E 2 and E 3 together with the carbon to which they are attached comprise a polycarbocyclic skeleton consisting of carbon and oxygen atoms. SUBSTITUTESHE 6. A process as set forth in claim 1 wherein the metal alkoxide has the following formula wherein Z is -OCOCH 3 or -OT 2 wherein T 2 is a hydroxy protecting group. 7. A process for the preparation of a taxane derivative comprising: providing a metal alkoxide having the formula MOCE j E-^, reacting the metal alkoxide with a β-lactam to form an intermediate, the β-lactam having the formula: wherein M is a metal, one of E- j^ , E 2 and E 3 is hydrogen and the other two of E j , E 2 and E 3 together with the carbon to which they are attached comprise a polycyclic skeleton. SUB S TITUTESHEET R-L is -ORg, -SR 7 , or -NRgRg, * R 2 is hydrogen, alkyl, alkenyl; alkynyl, aryl, or heteroaryl; R 3 and R 4 are independently hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, or acyl, provided, however, that R 3. and R 4 are not both acyl; R 5 is -COR 1Q ' -COOR 10 , -COSR 10 , -CONRgR 10 , -S0 2 R 11 , or -POR 1 R 13 , Rg is hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, hydroxy protecting group, or a functional group which increases the water solubility of the taxane derivative, R 7 is alkyl, alkenyl, alkynyl, aryl, heteroaryl, or sulfhydryl protecting group, R 8 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; Rg is an amino protecting group; R 10 is alkyl, alkenyl, alkynyl, aryl, or heteroaryl, R lχ is alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR 10 , or -NR 8 R 14 , R 12 and R 13 are independently alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR^g, or ~ NR 8 R 14' R 14 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; and converting said intermediate to the taxane derivative. 8. The process of claim 7 wherein R 2 and R 4 are hydrogen or lower alkyl, R 3 is aryl, R-^ is -ORg, and Rg is a hydroxy protecting group. SUBSTITUTESHEET 9. The process of claim 8 wherein R 3 is phenyl and R is -ORg wherein Rg is triethylsilyl, ethoxyethyl, or 2,2,2-trichloroethoxymethyl. 10. The process of claim 8 wherein the metal alkoxide is a metal alkoxide of 7-protected baccatin III. 11. The process of claim 8 wherein M is Li, Mg, Na, K or Ti. 12. The process of claim 7 wherein the metal alkoxide is derived from an alcohol having the formula: wherein T-^ is a hydroxy protecting group, Z is -OT 2 , and T 2 is acetyl or hydroxy protecting group. 13. The process of claim 7 wherein the metal alkoxide has the following formula: SUB S T I TUTESHEET wherein Z is -OCOCH 3 or -0T 2 wherein T 2 is a hydroxy protecting group and M is selected from the group comprising Li, Mg, Na, K and Ti. 14. The process of claim 7 wherein the β-lactam has the formula: or: wherein Rg is a hydroxy protecting group. 15. A process for the preparation of a taxane derivative comprising: providing a metal alkoxide having the formula MOCE 1 E 2 E 3 , reacting the metal alkoxide with a β-lactam to form an intermediate, the β-lactam having the formula: S UB S TITUTE SHE wherein M is a metal, one of E j , E 2 and E 3 is hydrogen and the other two of E j , E 2 and E 3 together with the carbon to which they are attached comprise a polycarbocyclic skeleton, R ± is -ORg, R 2 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; R 3 and R 4 are independently hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, or acyl, provided, however, that R 3 and R are not both acyl; R 5 is -COR 1Q , -COOR 1Q ' -COSR 1Q , -CONR 8 R 10 ' -S0 R 11 , or -POR 12 R 13 , Rg is hydrogen, alkyl, alkenyl, alkynyl, aryl, heteroaryl, hydroxy protecting group, or a functional group which increases the water solubility of the taxane derivative, R 7 is alkyl, alkenyl, alkynyl, aryl, heteroaryl, or sulfhydryl protecting group, R 8 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; Rg is an amino protecting group; R 10 is alkyl, alkenyl, alkynyl, aryl, or heteroaryl, R ± is alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR 10 , or -NR 8 R 14 , SUBSTITUTESHEET R 12 and R 13 are independently alkyl, alkenyl, alkynyl, aryl, heteroaryl, -OR^ Q , or -NRgR^ 4 , R 14 is hydrogen, alkyl, alkenyl, alkynyl, aryl, or heteroaryl; and converting said intermediate to the taxane derivative. 16. The process of claim 15 wherein the β-lactam has the formula: or: wherein Rg is a hydroxy protecting group. 17. The process of claim 16 wherein Rg is a hydroxy protecting group selected from the group consisting of triethylsilyl, ethoxyethyl, 2,2,2-trichloroethoxymethyl, trimethylsilyl, dimethyl-t-butylsilyl, dimethylarylsilyl, dimethylheteroarylsilyl, and triisopropylsilyl. SUBSTITUTE SHEET 18. The process of claim 16 wherein Rg is a hydroxy protecting group selected from the group consisting of triethylsilyl, 1-ethoxyethyl, and 2,2,2-trichloroethoxy- methyl. 19. The process of claim 15 wherein the metal alkoxide is derived from an alcohol having the formula: wherein T is a hydroxy protecting group, Z is -OT 2 , and T 2 is acetyl or hydroxy protecting group. 20. The process of claim 19 wherein said β-lactam is provided as a racemic mixture of β-lactam. S UBSTITUTESHEET

Inventors: HOLTON ROBERT A, HOLTON, ROBERT, A.
Applicants: UNIV FLORIDA STATE, FLORIDA STATE UNIVERSITY
Application year: 1992
Main classification: C07C229
IPC codes: C07C227, C07C229, C07C231, C07C233, C07D205, C07D305, C07D317, C07D407, C07D409, C07F7