INTERMEDIATES FOR THE PREPARATION OF THIENAMYCIN AND PROCESS FOR PREPARING INTERMEDIATES

Abstract: In a process for the total synthesis of thienamycin from L-aspartic acid via intermediate III: R = H, blocking group or salt cation there is disclosed a process for preparing III via wherein R is a protecting group.

Description: PROCESS FOR THE PREPARATION OF THIENAMYCIN AND INTERMEDIATES BACKGROUND OF THE INVENTION This invention relates to the total synthesis of the known antibiotic thienamycin (I). EMI1.1 Starting from L-aspartic acid, the synthesis proceeds in a stereo-selective way via intermediates II, III, IV: EMI2.1 wherein X is a conventional leaving group and R is hydrogen, a conventional, readily removable protecting group or a salt cation. This invention also relates to a process for preparing III via intermediate V: EMI2.2 wherein R is a protecting group. DETAILED DESCRIPTION OF THE INVENTION The process of the present invention may conveniently be summarized by the following reaction diagram: DIAGRAM I EMI3.1 EMI4.1 EMI5.1 EMI6.1 In words relative t the above diagram, L-aspartic acid 1 is esterified according to well known procedures. Typically 1 in a solvent such as benzene, toluene, chloroform or the like is treated with an esterifying agent such as benzyl alcohol, methanol, ethanol, ispropanol, or the like in-the presence of p-toluene sulfonic acid, HC1, HBr, or the like at a temperature of from 0 to 110 0C for from 1 to 24 hours to achieve the desired establishment and hence protection of the carboxyl functions. The resulting species 2 in a solvent such as ether, THF, DME or the like is treated with trimethylchlorosilane, or the like followed by treatment with EtMgBr, MeMgI, 3MgBr, t-BuMgCI, or the like at a temperature of from -40 to 500C for from 1 to 72 hours to provide azetidinone 3. Reduction of species 3 with a reducing agent such as NaBH4, or the like in a solvent such as methanol, ethanol, isopropanol or the like at a temperature of from -10 to 40 C for from 1 to 6 hours provides 4. (For purposes here, the symbols: Et, Me, , iPr, and t-Bu stand for: ethyl, methyl, phenyl isopropyl, and tert-butyl, respectively.) Treatment of # in a solvent such as methylene chloride, CHC13 or the like with methane sulfonyl chloride, methane-sulfonic anhydride or the like in the presence of a base such as Et3N, iPr2NEt, or the like followed by treatment with a stoichiometric to 5 fold excess of sodium iodide in acetone yields S via The transformation 5 establishes the protecting group R which may be a triorganosilyl group, such as t-butyldimethylsilyl, t-butyldiphenylsilyl, triphenylsilyl, isopropyldimethylsilyl, for example,or may be 3,4-dimethoxybenzyl, for example. Silyl protection is preferred, and typically R1 is established by treating 5 in a solvent such as dimethylformamide, acetonitrile, hexamethylphosphoramide, tetrahydrofuran and the like with a silylating agent such as t-butyldimethylchlorosilane, t-butyldiphenylchlorosilane, triphenylchlorosilane, and the like at a temperature of from -200 to 25 C for from 0.5 to 24 hours in the presence of a base such as triethylamine, diisopropylethylamine, or imidazole. The transformation 6 7 is accomplished by treating 6 in a solvent such as tetrahydrofuran, dimethoxyethane, diethylether or the like with a carbanion generically represented by the following structure: EMI8.1 wherein M is a metal cation such as lithium, potassium, copper or magnesium, for example, and R2, R3 and R4 are selected from alkyl, aryl or aralkyl such as methyl, ethyl, benzyl, methoxybenzyl, trityland phenyl, for example, at a temperature of from -100 to OOC and from 0.5 to 4 hours. Typically, the carbanion reagent is prepared prior to addition of substrate 6 on treatment of the triorganothiomethane with a strong base such as n-butyllithium, t-butyllithium, phenyllithium, lithium diisopropylamideOLDAL or the like. The alkylation 7¯+ 8 is accomplished by treating 7 in a solvent such as tetrahydrofuran, dimethoxyethane, diethy' ether, hexamethylphosphoramide, at a temperature of from -1000 to -200C with a strong base such as lithium diisopropylamide, lithium hexamethyldisilazide, lithium 2,2,6,6-tetramethylpiperidide, potassium hydride or the like followed by the addition of an equivalent to 10 fold excess of acetaldehyde. This reaction gives a mixture of isomers from which the desired trans-R form can be conveniently separated by chromatography or crystallization. The transformation 8--,9 9 is accomplished by treating 8 in a solvent such as methanol, ethanol, isopropanol, water or the like at a temperature of from 0 to 80 C with a Lewis acid such as mercuric chloride, silver tetrafluoroborate, thallium trinitrate or the like. The value of R5 is determined by the identity of the alcohol taken in reaction. The transformation 9 --, 10 establishes the hydroxyl protecting group R2. The most preferred protecting groups R2 are triorganosilyl groups such as t-butyldimethylsilyl, t-butyldiphenylsilyl, triphenylsilyl and the like. Typically, silylation is accomplished by treating t with the corresponding triorganosilyl chloride in a solvent such as dimethylformamide, acetonitrile,.tetrahydrofuran and the like at a temperature of from -20 to 800C for from 0.5 to 24 hours. The reduction 10- is accomplished by treating 10 in a solvent such as toluene, methylene chloride diethylether, tetrahydrofuran and the like with a reducing agent such as diisobutylaluminum hydride, sodium bis(2-methoxyethoxy)aluminum hydride or the like at a temperature of from -100 to -400C for from 1 to 10 hours. The addition 11#12 is accomplished by treating 11 in a solvent such as tetrahydrofuran, diethylether, dimethoxyethane or the like at a temperature of from -1000 to 0 C for from 15 minutes two 2 hours in the presence of LiCH2CO2R6; wherein R6 is benzyl, p-methoxybenzyl, 2,4-dimethoxybenzyl or the like; which reagent is typically generated in situ on treatment of the appropriate R6 acetate with a strong base such as LDA, lithium hexamethyldisilazide, lithium 2,2,6,6-tetramethylpiperide, or the like. If desired, a more readily removable carboxyl protecting group may conveniently replace the first established group, R6, by the carboxyl protecting group R7. This transformation 12-fi13 514 is accomplished by selectively deblocking 12 to form 13 by hydrogenation or hydrolysis. Typically, the reaction is accomplished by treating 12 in a solvent such as methanol, ethanol, dioxane, tetrahydrofuran, water or the like under a hydrogenation pressure of from 1 to 4 atmospheres in the presence of a catalyst such as Pd on charcoal, Pd(OH)2, or the like for from 0.1 to 10 hours. The 13 intermediate (M may be H, Na, K or ammonium such as Et3NH, for example) need not be isolated. Intermediate 14 is obtained from the hydrogenation mixture upon treatment with the chosen reagent calculated to establish R7 such as an aralkyl halide in a solvent such as dimethylformamide, acetonitrile, hexamethylphosphoramide at a temperature of from 0 to 50 C for from 0.5 to 18 hours. R7 is typically an aralkyl group such as p-nitrobenzyl, or o-nitrobenzyl, for example. The oxidation 14- > 15 is accomplished by treating 14 in a solvent such as methylene chloride, acetonitrile, or the like with an oxidizing system such as dipyridine chromium (VI) oxide, 3,5-dimethylpyrazole chromium (V') oxide, pyridinium chlorochromate, pyridinium dichromate, trifluoroacetic anhydride-dimethylsulfoxide, acetic anhydride-dimethyl sulfoxide or the like at a temperature of from -780C to 250C for from 5 min. to 8 hrs. Removal of protecting groups R1 and R2 (15#16) is accomplished by acidic aqueous hydrolysis of 15 in a solvent such as methanol, ethanol, tetrahydrofuran, dioxane or the like in the presence of an acid such as hydrochloric, sulfuric, acetic or the like at a temperature of from 0 to 1000C for from 2 to 18 hours. The diazo species 17 is prepared from 16 by treating 16 in a solvent such as CH3CN, CH2C12, THF or the like with an azide such as p-carboxybenzene sulfonylazide, toluenesulfonylazide, methanesulfonylazide or the like in the presence of a base such as triethylamine, -pyridine, (C2H5)2NH or the like for from 1 to 50 hours at 0-250C. Cyclization (17- > 18) is accomplished by tmating 17 in a solvent such as benzene, toluene, THF or the like at a temperature of from 50-1100C for from 1-5 hours in the presence of a catalyst such as bis (acetylacetonato)Cu (II) [Cu(acac)2], CUSO4, Cu powder, Rh(OAc)2, or Pd(OAc)2. Alternatively, the cyclization may be accomplished by irradiating 17 through a pyrex filter (a wave length greater than 300nm) in a solvent such as benzene, CCl4 diethylether or the like at a temperature of from 0-250C for from 0.5 to 2 hours.t"OAc" = acetate.] Establishment of leaving group X (; ;t is accomplished by acylating the keto ester 18 with an acylating agent ROX such as p-toluenesulfonic acid anhydride, p-nitrophenylsulfonic acid anhydride, 2,4, 6-triisopropylphenylsulfonic acid anhydride, methanesulfonic acid anhydride, toluenesulfonyl chloride, p-bromophenylsulfonyl chloride, or the like wherein X is the corresponding leaving group such as toluene sulfonyloxy, p-nitrophenylsulfonyloxy, methanesulfonyloxy, p-bromophenylsulfonyloxy and other leaving groups which are established by conventional procedures and are well known in the art. Typically, the above acylation to establish leaving groups X is conducted in a solvent such as methylene chloride, acetonitrile or dimethylformamide, in the presence of a base such as diisopropylethylamine, triethylamine, 4-dimethylamino-pyridine or the like at a temperature of from -20 to 400C for from 0.5 to 5 hours. The leaving group X of intermediate can also be halogen. The halogen leaving group is established by treating 18 with a halogenating agent such as #3PCl2, #3PBr2, (#O)3PBr2, oxalyl chloride or the like in a solvent such as CH2C12, CH3CN, THF, or the like in the presence of a base such as diisopropylethylamine, triethylamine, or 4-dimethylaminopyridine or the like. [ = phenyl.] The reaction 19-v20 is accomplished by treating 19 in a solvent such as dioxane, dimethylformamide, dimethylsulfoxide, acetonitrile, hexamethylphosphora- mide, or the like in the presence of an approximately equivalent to excess of the mercaptan reagent HSCH2CH2NHR8 wherein R is hydrogen or a readily removable N-protecting group such as p-nitrobenzyloxycarbonyl, o-nitrobenzyloxycarbonyl, or the like in the presence of a base such as sodium hydrogen carbonate, potassium carbonate, triethylamine, diisopropylethylamine, or the like at a temperature of from -40 to 25 C for from 1 to 72 hours. The mercaptan reagent, HSCH2CH2NHR8, is typically prepared by treating aminoethylmercaptan in the presence of the desired acid chloride in the presence of a base such as sodium bicarbonate, sodium hydroxide, or the like in a solvent such as aqueous diethylether, aqueous dioxane, aqueous acetone, or the like at a temperature of from 0 to 250C for from 0.5 to 4 hours. The final deblocking step 2%-I is accomplished by conventional procedures such as hydrolysis or hydrogenation. Typically 20 in a solvent such as dioxane-water-ethanol, tetrahydrofuran-aqueous dipotassium hydrogen phosphate-isopropanol or the like is treated under a hydrogen pressure of from 1 to 4 atmospheres in the presence of a hydrogenation catalyst such as palladium on charcoal, palladium hydroxide, or the like at a temperature of from 0 to 500C for from 0.5 to 4 hours to provide I. In the above-discussed aldol reaction 7-78 for introduction of the hydroxyethyl side chain, the scheme proceeds directly to give a mixture of isomers (trans-R, trans-S, and cis R) from which the desired trans-R isomer can be separated chromatographically or by crystallization. An indirect aldol reaction scheme stereo-selectively provides the desired trans-R isomer according to the following scheme: DIAGRAM II EMI14.1 wherein all symbols are as previously defined. In words relative to the above reaction scheme, Step A has been described above. The direct acetylation, Step B,is accomplished by treating 7 with two or more equivalents of a base such as lithium diisopropylamide, lithium hexamethyldisilazide, lithium 2,2,6,6-tetramethylpiperidide, in a solvent such as tetrahydrofuran, diethylether, or dimethoxyethane, for example, at a temperature of from -100 to -20 C with an acylating agent such as N-acetyl imidazole or the like. Addition of the 7 plus base mixture to the acylating agent is preferred. The oxidation Step C is accomplished with an oxidizing agent such as dipyridine chromium(V')oxide, trifluoroacetic anhydride,dimethylsulfoxide-triethylamine, pyridinium dichromate, acetic anhydride-dimethylsulfoxide in a solvent such as methylene chloride, acetonitrile, or the like at a temperature of from -78 to 25 C for from 5 minutes to 5 hours. The reduction Step D is accomplished by contacting the ketone with a reducing agent such as potassium tri(sec -butyl)borohydride, lithium tri (sec-butyl) borohydride, sodium borohydride, sodium tris(methoxyethoxy)aluminum hydride, lithium aluminum hydride or the like in a solvent such as diethylether, tetrahydrofuran, toluene or the like at a temperature of from -20 to 250C. The reaction can conveniently be conducted in the presence of an added complexing salt such as potassium iodide, magnesium bromide or the like. With reference to Diagram I, above, the present invention relates specifically to a process, and-to useful intermediates encountered along the way, for proceeding from 6 to 16 according to the following scheme: Diagram III EMI16.1 In words relative to Diagram III, all symbols are as previously defined; additionally, however, R and R3 may be joined together with a bridging radical such as EMI17.1 The radical R is newly encountered in this scheme and preferably is chosen from lower alkyl, such as methyl, ethyl or aryl, such as phenyl. The transformation 6 # 21 is accomplished in a manner analogus to the transformation 6 o7 (Diagram I) except that the carbanion is generically represented by the following structure: EMI17.2 wherein all symbolism, including M, is as defined above. Intermediate 21 may proceed directly to 22 in a manner exactly analogous to the transformation 73 8 (Diagram I) or it may take the circuitous path via 22a. The transformation 21 # 22a # 22 is conducted in a manner exactly analogous to the scheme: : EMI17.3 <tb> 7 <SEP> (B) <SEP> (D) <SEP> 8 <tb> (Diagram'II). The transformation EMI17.4 is accomplished in a manner exactly analogous to the step 8# 9 of Diagram I. The oxidation EMI17.5 is preferably achieved with a 1.0 to 5.0 fold excess of an oxidizing agent such as m-chloroperbenzoic acid, peracetic acid, hydrogen peroxide, pertrifluorocicetic acid, or the like, in a solvent such as chloroform, carbcntetrachloride, chlorobenzene, or the like, at a temperature of from 20C to 1300C for from 0.5 to 24 hours. S 10 15 20 25 30 The addition EMI18.1 is accomplished by treating 24 with l,l'-carbonyldimidazole, or the like, in a solvent such as tetrahydrofura dimethoxyethane, or the like, at a temperature of from 100 to 50 C followed by the addition of 1.1 to 3.0 equivalents of (R o2CCH2CO2)2Mg, or the like, at a temperature of from -10 to 500C for from 1 to 48 hours. The deblocking of 25 to yield 16 is accomplished exactly as described for the deblocking EMI18.2 (Diagram 7). The remainder of the synthesis is exactly as described above Diagram I), picking up at 16. The synthesis described by foregoing schemes I and II (Diagrams I and II) and steps from 16 to thienamycin are described and claimed in co-pending European Patent Application Serial Number 79101307.1- filed May 1, 1979); this application is incorporated herein by reference. In the foregoing word description of the above schematic reaction diagram for the total synthesis of thienamycin, it is to be understood that there is considerable latitude in selection of precise reaction parameters. Suggestion of this latitude and its breadth is generally indicated by the enumeration of equivalent solvent systems, temperature ranges, protecting groups, and range of identities of involved reagents. Further, it is,to be understood that the presentation of the synthetic scheme as comprising distinct steps in a given sequence is more in the nature of a descriptive convenience than as a necessary requirement; for one will recognize that the mechanically dissected scheme represents a unified scheme of synthesis and that certain steps, in actual practice, are capable of being merged, conducted simultaneously, or effected in a reverse sequence without materially altering the progress of synthesis. The following examples recite a precise scheme of total synthesis. It is to be understood that the purpose of this recitation is to further illustrate the total synthesis and not to impose any limitation. EXAMPLE 1 Preparation of 4(S)-4-Iodomethylazetidin-2-one STEP A EMI20.1 Benzyl (S)-azetidin-2-one-4-carboxylate To a 1000 ml separatory funnel are added dibenzyl (S)-aspartate rtoluenesulfonic acid salt (48.6 g, 0.1 mole), ice-cold diethyl ether (300 ml), ice-cold water (100 ml), and ice-cold saturated aqueous potassium carbonate (50 ml). The mixture is shaken vigorously and the layers are separated. The aqueous portion is extracted with more cold diethyl ether (2 x 100 ml). The combined ether solution is washed with brine, dried with magnesium sulfate, and evaporated under vacuum to provide dibenzyl (S)aspartate (31.4 g, 0.1 mole) as a colorless liquid The dibenzyl (S)-aspartate in anhydrous diethyl ether (200 ml) is cooled in an ice-bath under a nitrogen atmosphere. Trimethylchlorosilane (12.7 ml, 0.1 mole) is added to the stirred solution to give a white precipitate. Triethylamine (14.0 ml, 0.1 mole) is then added to the mixture. The cooling bath is removed and the mixture is stirred at room temperature (22-250C) for 2 hrs. The mixture is then filtered directly into a 3-neck, 1.0 liter, round bottom flask fitted with a sintered glass funnel, magnetic stirrer, and a vacuum-nitrogen inlet. This operation is carried out under a blanket of nitrogen, care being taken to exclude atmospheric moisture. The sintered glass'funnel is replayed by a stopper and the ether is evaporated under vacuum with stirring to provide dibenzyl (S)-N-trimethylsilylaspartate (35.5 g, 0.092 mole) as a slightly hazy oil. Anhydrous diethyl ether (250 ml) is added to the flask containing the silyl derivative and the magnetic stirrer is replaced by a mechanical stirrer. The resulting solution is stirred under a nitrogen atmosphere with ice-bath cooling. Ethereal ethyl magnesium bromide (34 ml of a 294 M solution, 0.1 mole) is added dropwise over 40 min. to give a cream colored, stirable precipitate. The cooling bath is removed and the mixture is stirred at room temperature. After 1.5 hrs, a viscous gum forms. The mixture is allowed to stand overnight at room temperature. The mixture is then cooled in an ice-methanol bath while ammonium chloride saturated 2N hydrochloric acid (100 ml) is added slowly with stirring. The resulting mixture is diluted with ethyl acetate (100 ml) and water (100 ml) and the layers are separated. The aqueous portion is extracted with more ethyl acetate (3 x 100 ml). The combined organic solution is washed with water (200 ml), 5% aqueous sodium bicarbonate solution (100 ml), water (100 ml), and brine, dried with magnesium sulfate, and filtered. Evaporation of the solvent under vacuum gives an orange oil interspersed with a fine, granular precipitate (25.3 g). This material is dissolved in warm chloroform (75 ml), diluted with petroleum ether (125 ml), seeded, scratched, and cooled in an ice-bath. The preci- pitate is collected, washed with petroleum ether, and dried under vacuum to give benzyl (S)-azetidin2-one-4-carboxylate (3.85 g) as an off-white solid mp 136-139 C. The mother liquors and washings are combined, diluted with petroleum ether to 500 ml, seeded, and left in a refrigerator for several days. The resulting precipitate is collected, washed with petroleum ether, and dried under vacuum to give additional product (0.82 g) as pale yellow crystals. Recrystallization of a-sample from chloroform-petroleum ether gave the product as small, white flakes: mp 141-143 ; [a) D= -43.4 (c3.275 in CHCl3); IR(CHC13) 3425, 1778, 1746 cm-Ú; 1H NMR(CDCl3) 3.00 (ddd, 1,J= 1.9, 3.2, and 14.6 Hz, H-3a) ,(3.35 (ddd, 1, J = 1.5, 5.4, and 14.6 Hz, H-3b), # 4.20 (dd, 1, J = 3.2 and 5.4 Hz, H-4), r5.22 (s, 2, OCH2Ph), 6.48 (m, 1, NH), 7.38 (s, 5, phenyl); mass spectrum m/e 205 (M+), 163, 91, 70, 43. Anal. Calcd. for C11H11NO3: C, 64.38; H, 5.40; N, 6.83. Found: C, 64.10; H, 5.70; N, 6.77. STEP B EMI23.1 4(S)-4-Hydroxymethylazetidin-2-one Sodium borohydride (3.69 g, 97.5 mmol) is added in one portion to a suspension of benzyl 4(S)azetidin-2-one-4-carboxylate (20.0 g, 97.5 mmol) in 300 ml of absolute methanol at 0 C. The mixture is then allowed to warm slowly with periodic cooling being supplied to keep the internal temperature < 300C. After stirring for 2 hr., glacial acetic acid (23.4 g, 390 mmol) is added and the reaction mixture is concentrated under vacuum. The residue is treated with 500 ml of chloroform and filtered. The filtrate is concentrated under vacuum and the residue is chromatographed on 250 g of silica gel (4:1, chloroform: methanol) to yield 9.62 g (98%) of 4(S)-hydroxymethylazetidin-2-one as a white solid: m.p. 51-53 C; [&alpha;]D=+68.0 (C=2.676 in CHCl3); IR (CHC13) 3410, 1765 cm 1H NMR (CDCl3) # 7.07 (1H, br. s, NH), # 4.05 (1H, br. s, OH), # 3.77 (2H, m H4, H-5a or b), 3.58 (1H, dd, J=11, 6, H-5a or b), # 2.97 (1H, ddd, J= 14.5, 4.8, 1.3, H3b), # 2.7 (1H, br. d, J=14.5, H3a); mass spectrum m/e 101 (M+), 83. STEP C EMI24.1 4(S)-4-Methanesu > ionyloxymethyl azetidin-2-one Metbane,isulfonyl chloride (11.46 g, 100 mmol) is added dropwise by syringe to a solution of 4(S)-4-hydroxymethyl azetidin-2-one (10.1 g, 100 mmol) and triethyl amine (10.1 g, 100 mmol) in 15 ml of dry methylene chloride at OOC. (Warming is necessary in order to initially solubilize the alcohol. The resulting solution is then cooled to 0 C prior to addition of the other reagents). The resulting solution is stirred at 0 C for 1 hr. during which time a voluminous precipitate is produced. At the end of this time, the reaction mixture is filtered and the filtrate is concentrated under vacuum. The two solid residues are combined and treated with 500 ml of chloroform. The resulting mixture is filtered to yield substantially pure 4(S)-4-methanesulfonyloxymethyl azetidin-2-one as a white solid. The filtrate, which contains most of the triethylamine hydrochloride, is concentrated under vacuum and chromatographed on 200 g of silica gel (4:1 chloroform:methanol) to yield an additional quantity of mesylate. This material is combined with that obtained previously and recrystallized from chloroform to yield 15.57 g (87%) of 4(S)-4methanesulfonyloxymethylazetidin-2-one as colorless needles: m.p. 109.5-110.5 C; [&alpha;]D=+25.8 (C=1.025 in H2O); NMR (D20) g 4.62 (lH,-dd, J=11.2, 3.0, H-5a or b), # 4.43 (1H, dd, J= 11.2, 6, H-5a or b), # 4.12 (1H, m, H4) # 3.26 (3H, EMI25.1 # 3.19 (1H, dd, J=15, 4.5,H3b). 2.88 (1H, dd, J=15, 2.5, H3a); mass spectrum m/e 179 (M+),136; Anal: Calc: C, 33.51; H, 5.06; N, 7.82; S, -17.89 Found: C, 33.54; H, 5.08; N, 7.72; S, 17.93 STEP D EMI25.2 4(S)-4-Iodomethylazetidin-2-one A mixture of 4 (S)-4-methanesulfonyloxy azetidin 2-one (11.8 g, 65.9 mmol) and powdered sodium iodide (19.8 g, 132 mmol) in 130 ml of acetone is heated at reflux for 6 hr. The resulting reaction mixture is concentrated in vacuo, treated with 200 ml of chloroform and filtered. The filtrate is washed with 2 X 50 ml of water and dried over magnesium sulfate. The organic phase is filtered, concentrated in vacuo, and chromatographed on 250 g of silica gel (ethyl acetate) to yield 11.94 g (86%) of 4(S)-4-iodomethyl-azetidin2-one as a white solid. This material is recrystallized from ether-petroleum ether to yield white crystals: mp 91-920C; [al= -23.70 (C= 1.354 in CHCl3) ; IR (CHCl3) 3450, D1765 cm-1, 1H NMR (CHCl3) @ 6.13 (brs, N-H), @ 3.94 (m, 1 H, Hc), @ 3.36 (m, 2H, Hd and e), @ 3.16 (ddd, 1H, J=14.9, 5.4, 2.3, Ha) , @ 2.72 (d, d, d, 1H, J=14.9, 2.1, 2, Hb) mass spectrum m/e 211 (M+), 168, 142, 127, 84. EXAMPLE 2 Preparation of (4S)-1-(t-Butyldimethylsilyl)-4-iodomethylazetidin-2-one EMI27.1 t-butyldimethylchlorosilane (7.51 g, 49.8 mmol) is added in one portion to an ice-cold, stirring solution of (4S) 4-iodomethyl-azetidin-2-one(10,0g, 47.4mmol) and triethylamine (5.04g, 49.8 mmol) in anhydrous dimethylformamide (100 ml). A voluminous white precipitate forms almost immediately. The reaction mixture is stirred at 0-5 for 1 hour and then allowed to warm to room temperature. Most of the solvent is removed under vacuum to give a.residue which is partitioned between diethyl ether (250 ml) and water. The ethereal phase is washed with 2.5N hydrochloride acid (50 ml), water (3x50 ml), and brine, dried with magnesium sulfate, filtered, and evaporated under vacuum to provide (4S)-l-(t-butyldimethylsily 4-iodomethyl-azetidin-2-one (15.1 g) as a white solid. Recrystallization from petroleum ether - ethyl ether gives the product as colorless plates, mp 71-720; ; n.m.r. (CDCl3), #3.l8 (m,l), # 2.6-3.6 (2 overlapping d of AB, 4) # 1.0 (S,9),j0.3(S,6),0.25(S,6). Preparation of (45) (4S)-l-(t-Butyldimethylsilyl)-4 (2,2,2-tri(methylthio)-ethyl)axetidin-2-one EMI28.1 n-Butyllithium (19.4 ml of 2.5M hexane,solution, 48.5 mmol) is added slowly by syringe to a solution of tri(methylthio)methane (7.47g, 48.5 mmol) in 150 ml of freshly distilled THF at -780C. The resulting solution is stirred at -78C for 30 min. prior to the addition of a solution of (4S)-1- (tert-butyldimethylsilyl) -4-iodomethylazetidin-2-one (15.0g, 46.15 mmol) in 50 ml of THF. This solution is stirred at -780C for 30 min., then quenched by addition of saturated aqueous ammonium chloride solution. The reaction mixture is allowed to warm to room temperature, then poured into ether (250 ml), washed with water (2x100 ml) brine (100 ml) and dried over magnesium sulfate. Removal of solvents in vacuo gives an oil which is crystallized from petroleum ether to give 13.3g (82%) of (4S)-1-(t-butyldimethyl- silyl)-4-(2,2,2-tri(methylthio)ethyl)azetidin-2-one as colorless prisms. m.p. 61-62 C. IR(CHC13,CM 1) 2913, 2850,1730; n.m.r. (CDCl3) # 4.0 (m,l), # 3.35 (dd,1,J=5,16), 2,83(dd,1,J=3,16) S 2,5(ABq,2) i 2,15(s,9), 0.98(s,9), #0.25 (z,6) EXAMPLE 4 Preparation of (3S, 4R)-1-(t-butyldimethylsily)-3- [(R)-1-hydroxyethyl]-4-(2,2,2-tri(methylthio)ethyl)azetidin-2-one EMI29.1 n-Butyllithium (14.8 ml of 2.5N hexane'solution, 37.0 mmol) is added by syringe to a solution of diisopropylamine (3.74g, 37.0 mmol) in 180 ml of freshly distilled tetrahydrofuran at -780C. The resulting solution is stirred at -780C for 15 min prior to the addition of a solution of (4S)-l-(t butyldimethylsilyl) -4- [2,2, 2-tri (methylthio) ethyl] azetidin-2-one (12.34g, 35.16 mmol) in 35 ml of tetrahydrofuran. This solution is stirred at -780C for 10 min prior to the addition of acetaldehyde (4.62g, 105 mmol). The solution is stirred for an additional 5 min. at -780C and then quenched by addition of saturated aqueous ammonium chloride solution, and allowed to warm to room temperature. The mixture is poured into 250 ml of ether and washed with water (2 x 100 ml) and brine and dried over magnesium sulfate. Removal of solutions in vacuo gives an oil which is chromatographed on a silica gel column (1:1 ether: petroleum ether) to give (3S,4R)-1-(t-butyldimethylsilyl)- 3- (R) -l-hydroxyethyl] -4- [2, ,'2Ttri (methylthio) ethyl] - azetidin-2-one (3.(1g,- 5Q.4tL at Rf-0.2. The product can be recrystallized from petroleum ether. Alternatively, t trans R product can be isolated from the crude reaction mixture by direct crystallization from a petroleum ether solution. EXAMPLE 5 Preparation of (3S,4R)-l-(t-Butyldimethylsilyl)-3-(l- oXoethyl)-4-[2,2,2,-trilmethylthio)ethyl]azetidin-2-one EMI30.1 A. n-Butyllithium (2.43 ml of 2.4m solution, 5.84 mmol) is added by syringe to a solution of diisopropylamine (591 mg, 5.84 mmol) in 25 ml of freshly-distilled tetrahydrofuran at -780C. The resulting solution is stirred at -780C for 15 minutes prior to the addition of a solution of (4R)-1-(t-butyldimethylsilyl)-4- [2,2,2-tri(methylthio) ethyl]azetidin-2-one (1.00 g, 2,85 mmol) in tetrahydrofuran (5 ml). This solution is stirred at -78 C for 15 minutes, then added via a Teflon tube to a mixture of N-acetylimidazole (642 mg, 5.84 mmol) in 25 ml of THF at -780C. The resulting yellow reaction mixture is stirred at -780C for 10 minutes, then quenched by addition of saturated aqueous ammonium chloride solution. The mixture is diluted with ether (200 ml) and washed with 2.5N hydrochloric acid solution (50ml), water (50 ml) and brine (50 ml) and dried over magnesium sulfate. Removal of solvents in vacuo gives a yellow oil which is chromatographed on silica gel (30% ether in petroleum ether) to yield (3S, 4R)-l-(t-butyldemethylsilyl)-3-(1-oxoethyl)-4-[2,2,2-tri (methylthio)ethyl) azetidin-2-one. n.m.r. (CDCl3) # 4.42 (m,1), # 4.32 (d,l) # 2.35 (m,2), # 2.32 (s,3), # 2.2 (s,9), # 0.98 (s,9), # 0,3 (2s,6). B. Trifluoroacetic anhydride (400 mg., 1.905 mmol) is added by syringe to a solution of dimethyl sulfoxide (2.53 mmol) in dry methylene chloride (5 ml) at -780C. The resulting mixture is stirred at -780C for 30 minutes prior to the addition of a solution of(3RS, 4R)-1-(t- butyldlimethylsilyl) -3- [ (RS) -l-hydroxyethyl] -4- [2,2,2tri(methylthio)ethyl] azetidin-2-one (500 mg., 1.27 mmol) in dry CH2cl2(1 ml). The resulting solution is stirred for 30 minutes prior to the addition of triethylamine (360 mg., 3.56 mmol). The cooling bath is removed. After 40 minutes, the reaction mixture is diluted with CH2C12, washed with water and brine and dried over magnesium sulfate. Removal of solvents in vacuo gives an oil which is purified as above. Yields 432 mg. (86%). EXAMPLE 6 Preparation of (3S,4 R)-l-(t-butyldimethylsilyl)-3-[(R)- 1-hydroxyethyl]-4-[2,2,2-tri(methylthio)ethyl] azetidin-2one EMI32.1 K-5electride (3,64 mi of 0.5M, 1.82 mmol) is added by syringe to a mixture of potassium iodide t126 mg.,0.758 mmol) and (3S,4R)-1-(t-butyl dimethylsilyl)-3-(1-oxoethyl)-4 (2,2,2-tri (methylthio)etnhylazetidin-2-one (298 mg, 0758 mmol) in freshly distilled ethyl ether (8 ml) at room temperature. The resulting mixture is stirred at room temperature for 2.5 hours, then quenched by the addition of acetic acid (218 mg., 3.64 mmol). The resulting mixture is diluted with ethyl acetate (25 ml) and filtered through celite. Removal of solvents in vacuo gives an oil which is chromatographed on silica gel (ether:petroleum ether) to yield 252 mg of(3S, 4R)-l-(t-butyldimethylsilyl)-3-l(R)-l-hydroxyethyl]- | 4- (2 ,2,2-tri (methylthio) ethyl] azetidin-2-one. N.M.R. (R isomer, CDCl3+D2O) # 4.15 (dg,1), # 3.95 (ddd,1,J=9.5,2.3), #3.26(dd,1,J=8,2.3), #2.37 (m,2), # 2.16(s,9), # 1.37 (d,3,J= 6,6), # 1.0 (s,9), # 0.26 (s,6). EXAMPLE 7 Preparation of C3S,4R)-l-Ct-Butyldimethylsilyl)-3- AR)-l-hydroxyethyl)-4-carbomethoxymethylazetidin-2- EMI33.1 Mecuric chloride (12.37g, 45.6 mmol) is added in one portion to a solution of (3S,4R)-l-(t-butyldimethylsilyl)-3-[(R)-1-hydroxyethyl]-4-(2,2,2-tri(methylthio)ethyl] azetidin-2-one (6,0g, 15.2 mmol) in 250 ml of absolute methanol at O C. The resulting mixture (heavy white precipitate) is stirred at 0 C for 3 min., then quenched by addition of sodium bicarbonate (8.99 g,l07mmol). This mixture is then filtered and the solid residue is washed with additional methanol. The combined filtrate and washings are concentrated in vacuo and the residue is partitioned between ethyl acetate and saturated aqueous ammonium chloride solution. The organic phase is separated, washed with saturated aqueous ammonium chloride solution, water and brine and dried over magnesium sulfate. Removal of solvents in vacuo gives an oil which is chromatographed on a silica gel column (3:2 cyclohexane: ethyl acetate) to yield (35, 4R)-1-(t-butyldimethylsilyl)- 3-1(R)-1-hydroxyethyl)]-4-carbomethoxymethyl azetidin-2one. EXAMPLE 8 Preparation of (3S,4R)-1-(t-Butyldimethylsilyl)-3l(R)-l-(t-butyldimethylsilyloxy)ethyll-4-arbometh methvlazetidin-2-one EMI34.1 t-Butyldimethylchlorosilane (940 mg, 6.25 mmol) is added in one portion to a solution of (35, 4R)-1- (t-butyldimethylsilyl)-3-[(R)-1-hydroxyethyl]-4 carbomethoxymethylazetidin-2-one (1.88g, 6.25 mmol) and triethylamine (1.27 g, 6.25 mmol) in 15 ml of anhydrous diemthylformamide at 0.C. After 15 min. at 0 C the cooling bath is removed and the reaction mixture is stirred at room temperature for 24 hrs. Ether (100 ml) is added and the mixture is filtered, then washed with 2.5N hydrochloric acid-(20 ml), water (3x20 ml) and brine. The organic phase is dried over magnesium sulfate, then concentrated in vacuo. The residue is chromatographed on silica gel (7:3 petroleum ether:ether) to yield (3S, 4R)-l-(t-butyldimethyl sityl)-3-[(R)-l-tt-butyldimethylsilyloxy)ethyl]-4- carbomethoxymethylazetidin-2-one. n.m.r. (CDCl3)#4.1(m,2), #3.68 (S,3), # 3,09 (dd,1,J=4.3,2.7), #2.8 (ABq,2), #1.17(d,3, J=6.6), #0.98 (s,9), #0.89(s,9), #0.23 (s,6), #0.1(s,6). EXAMPLE 9 Preparation of (3S,4R) -l-Lt-Butyldirnethylsilyl) -3- [(R)-1-(t-butyldimethylsilyloxy)ethyl]-4 (2-oxoethyl) azetidin-2-one EMI35.1 Diisobutylaluminum hydride (3.72 ml of 0.91 M in hexane, 3.38 mmol) is added slowly by syringe to a solution of (3S, 4R)-1-(t-butyldimethylsilyl)-3-[(R)-1-(tbutyldimethylsilyloxy)ethyl)-4-carbomethoxymethyl azetidin-2-one (936 mg, 2.26 mmol) in 25 ml of freshly distilled toluene at -780C. The resulting solution is stirred at -78 C for 3 hrs., then quenched by addition of 2.5N hydrochloric acid (5 ml). The resulting mixture is stirred for 2 min., then poured into a separatory funnel containing 100 ml of ether and 50 ml of 1.25N hydrochloric acid saturated with tartaric acid. The organic phase is separated and the aqueous phase is extracted with ether (2x50 ml). The combined organic phases are washed with brine and dried over magnesium sulfate. Removal of solvents in vacuo gives a white solid which is recrystallized from ether-petroleum ether to give (3S,4R)-1-(t-butyldimetjylsilyl)-3-[(R)-1 (t-butyldimethylsilyloxy)ethyl]-4-(2-oxoethyl)azetidin-2-one- m.p. 115-116 C; n.m.r. (CDCl3) # 4.1 (m,1), # 4.03 (m,1), # 2.7-3.2 (m,3), # 1.23 (d,3,J=6.4), #1.08 (s,9), #0.9(s,9), #0.25(s,6), #0.1(s,6), #9.83(t, 1, J=1.4). EXAMPLE 10 Preparation of (3S, 4R)-1-(t-Butyldimethylsilyl)-3 [(R)-1-(t-butyldimethylsilyloxy)ethyl]-4-(3benzyloxycarbonyl-2-hydroxypropyl)azetidin-2-one EMI36.1 n-Butyllithium (1.81 mmol) is added by syringe to a solution of diisopropylamine (1.81 mmoi) in 9 ml of freshly distilled tetrahydrofuran at -780C. The resulting solution is stirred for 15 min at -780C Benzyl acetate (1.81 mmol) is then added dropwise by syringe and the resulting solution is stirred at -780C for 20 min. A solution of (3S, 4R)-l-(t-butyldimethyl silyl)-3-[(R)-l-(t-butyldimethylsilyloxy)ethyl]-4- (2-oxoethyl)azetidin-2-one (1.64 mmol) in 3 ml of anhydrous tetrahydrofuran is added slowly by syringe. The reaction mixture is stirred at -780C an additional 15 min and then quenched by addition of saturated aqueous ammonium chloride solution. Ethyl acetate -' (50 ml) is added and the organic phase is separated, washed with water (2x10 ml) and brine and dried over magnesium sulfate. Removal of solvents in vacuo gives a white solid which is chromatographed on a short silica gel column (40% ether in petroleum ether) to yield (3S,4R)-l-(t-butyldimethylsilyl)-3-[(R)-l-(t-butyldimethyl- silylOxy)ethyl]-4-(3-benzyloxycarbonyl-2-hydroxypropyl)- azetidin-2-oneS n.m.r. (CDC13) 7.32(s,5), #5,1(s,2), # 4.0(m,3), #2,4-3,8(m,4), # 2.0(m,2), # 1.25(overlapping d, 3), #0.05(s,9), # 0.9 (s,9), # 0.3 (s,6), # 0.18 (s,6). EXAMPLE 11 Prepaation of (3S,4R)-1-(t-Butyldimethylsilyl)-3 [(R)-l-(t-butyldimethylsIlyloxy)ethyll-4-[3-(4- nitrobenzyl)oxycarbonyl-2-hydroxypropyl]azetidin-2-one EMI37.1 A mixture of (3S,4R)-1-(t-butyldimethylsilyl)-3- [(R)-1-(t-butyldimethylsilyloxy)ethyl]-4-(3benzyloxycarbonyl-2-hydroxypropyl)azetidin-2-one (1.00 mmol), sodium bicarbonate (1.00 mmol) and 10% Pd/C in 20 ml of 4:1 tetrahydrofuran-H2O is hydrogenated at 40 psi on a Parr shaker for 30 min. The mixture is then filtered through Celite and the catalyst is washed with 10 ml of water. The combined washings and filtrate are concentrated i.v. to 2 ml and lyophilized. The resulting fluffy white solid is dissolved in 5 ml of anhydrous dimethylformamide and p-nitrobenzyl bromide (216 mg, 1.00 mnl) is added in one portion. The resulting solution is stirred at room temperature for 3 hrs, then diluted with ether (50 ml) and washed with water (3x10 ml) and brine and dried over magnesium sulfate. The solvents are removed in vacuo and the residue is chromatographed on silica gel to yield (3S,4R)-l-(t-Butyldimethylsilyl) 3[(R)-1-(t-butyldimethylsilyloxy)ethyl]-4-[3-(4-nitrobenzyl)oxycarbonyl-2-hydroxypropyl]azetidin-2-one, n.m.r. (CDCl3) & .85(2d-x=atin,4), S5,26(s,2),; 4.2(m,3), 2,5-3.6(m,4) # 2.0 (m,2) , # 1.4(2 overlapping d,3), # 1.0 (2s, 18), #0.25 (2s,12). EXAMPLE 12 Preparation of (35, 4R) -1- (t-Butyldimethylsilyl) -3- [(R)-1-(t-butyldimethylsilyloxy)ethyl]-4-[3-(4nitrobenzyl)oxycarbonyl-2-oxopropyl]azetidin-2-one EMI38.1 Anhydrous chromium trioxide (10.0 mmol) is added to a soution of anhydrous pyridine (20.0 mmol) in 30 ml of anhydrous methylene chloride. After stirring at room temperature for 15 min., the reaction mixture is treated all at once with a solution of (3S,4R)-1 (t-butyldimethylsilyl) -3- ((R) -1- (t-butyldimethylsilyloxy) ethyl -4-[3-(4-nitrobenzyl) oxycarbonyl-2-hydroxypropyi] - azetidin-2-one (1.00 mmol) in annydrous methylene chloride (8 ml). The resulting mixture is stirred at room temperature for 5 min. The CX2C12 layer is decanted from the dark, tarry residue which is triturated with more CH2C12. The combined CH2C12 phase is concentrated in vacuo. The residue is triturated with ether (100 ml) and the ether extracts are filtered. The filtrate is washed with 5% aqueous sodium bicarbonate solution, 2.5N HC1, 5% NaHCO3 and brine, dried over magnesium sulfate and concentrated in vacuo to yield (35 4R) -1- (t-butyldimethylsilyl) -3- [(R) -1- (t-butyldimethyl- silyloxy) ethyl] -4- [3- (4-nitrobenzyl) oxycarbonyl-2oxopropyl]azetidin-2-one. n.m.r. (CDCL3) # 7.85(2d-aromatic, 4), #5.27(s,2), # 4.05(m,2), # 2.6(s,2), # 2.4-3.2(dd over- lapping ABq,3), # 1.2(d,3,J=6.6), # 0.9(2s,18), # 0.22(s,6), # 0.05(s,6). EXAMPLE 13 Preparation of (3S,4R)-3-t(R)l-hydroxyethyl]-4-[3- (4-nitrobenzyl)oxycarbonyl-2-oxopropyl]azetidin-2-one EMI39.1 (3s,4R)-1-t-butylaimethylsilyl)3-[(R) Il-(t-butyl- dimethylsilyloxy)ethyl]-4-[3-(4-nitrobenzyl)oxycarbonyl2-oxopropyl]azetidin-2-one (7.9 mmol) is dissolved in 160 ml of 9:1 (v/v) methanol-water and cooled to 0 C. Concentrated hydrochloric acid (2.75 ml) is added and the resulting solution is stirred at 0 C for 15 min., then allowed to warm to room temperature. The solution is stirred at room temperature for 2.5 hrs, then diluted with ethyl acetate (200 ml) and washed with water, saturated aqueous sodium bicarbonate solution and brine, dried over magnesium sulfate and concentrated in vacuo to yield (3S, 4R)-3-[(R)1-hydroxyethyl]-4-[3-(4- nitrobenzyl)oxycarbonyl-2-oxopropyl]-azetidin-2-one. EXAMPLE 14 Preparation of (3S,4R)-3-[(R)-1-hydroxyethyl)-4-[3-(4 nitrobenzyl) oxycarbony1-2-oxo-3-diazoropyl] azetidin-2-one EMI40.1 wiethylamine(263 mg, 2.6mmol) is added by syringe. to a mixture of (3S,4R)-3-[(R)- l-hydroxyethyl] -4- 13- (8-nitrobenzyB oxycarbonyl-2-oxopropyl]azetidin-2-one(253mg, 0.72 mmol) and p-carboxybenzene sulfonylazide (196 mg, 0.84 mmol) in dry acetanitrile (6 ml) at0 C. When addition is complete the cooling bath is removed and the reaction mixture is stirred at room temperature for 1 hour. The mixture is then diluted with ethyl acetate (50 ml) and filtered. The filtrate is concentrated in vacuo and the residue is chronatographed on a short silica gel column.. (ethyl acetate) to yield 222 mg, (81% overall from (3S, 4R)-1-(t-butyldimethyl- silyl)-3-t(R)-l-(t-butyl dimethylsilyloxy)ethyl]-4-13- (4-nitrobenzyl) oxycarbonyl-2-oxopropyl] azetidin-2-one) of (3S,4R)-3-(R)-1-hydroxyethyl)-4-[3-(4-nitrobenzyl)oxycarbonyl2-oxo-3-diazopropyl]azetidin-2-one as a white solid m.p. (dec.) 1630C. IR(CHC13, CM 1) 3410, 2132, 1756, 1718, 1650, 1350, 1280, 1120; n.m.r. (CDCl3)#7.9 (2d-aromatic,4), #5.4(s,2), #6.2(brs,1), #4.1(m,2), $2.6-3.6(m,4), #1.32 (d,3,J=6.2). EXAMPLE 15 Preparation of -(5R,6S) p-Nitrobenzyl 6-[(R)1-hydroxyethyl]- 1-azabicyclo[3.2.0]heptap-3,7-dione-2-craboxylate EMI41.1 A suspension of (3S,4R)-3-[(R)-1-hydroxyethyl]-4-[3- [4-nitrobenzyl)oxycarbonyl-2-oxo-3-diazopropyl]azetidin2-one (56.4mg, 0.15 mmol) and rhodium (II) acetate (0.1 mg) in dry benzene (3ml) is deoxygenated by bubbling through nitrogen for 10 minutes. The mixture is then heated to 780C for 1 hour. During heating the solid starting material gradually goes into solution. The mixture is then cooled, filtered to remove the catalyst, and the filtrate is concentrated in vacuo to yield (5R, 6S) p-nitrobenzyl 6-f(R)- 1-hydroxyethyl]-1-azabicyclo[3.2.0]heptan-3,7.dione-2-carboxy= late, 51 mg. (98%) as a colorless oil which slowly crystallized t room temperature (220C). Physical Properties: EMI41.2 PNB= p-nitrobenzyl n.m.r.: (300MHz, CDC1 (#8.26, 7.54(aromatic, 4), 5.29 (AB,2), 4.77 (s,l), 4.32 (dg.1,J=6.6,7), 4.16(ddd,l,J=7,7.5,2.2), 3.21(dd,1,J=7,2.2), 2.94(dd,1,J=19.5,7) 2.50(dd,1,J= 19.5,7.5), 2.2(brs,l), 1.37(d,3,J=6.6). I.R.: (CHCl3,CM-Ú) 1770, 1758, 1610, 1522, 1353 m.p. 110-111 C. EXAMPLE 16 Preparation of p-Nitrobenzyloxycarbonylaminoethanethiol EMI42.1 To 600 ml diethyl ether (Et2O) - 75 ml H2 0 in an ice bath with stirring is added 3.2 g cysteamine hydrochloride (mw = 114; 28.1 mmole). A solution of 7.14 g NaHCO3 (mw = 84; 85 mmole) in 75 ml H2O is added. The ice bath is removed, and at room temperature a solution of 6.75 g - nitrobenzylchloroformate (mw = 216; 31.3 mmole) in 270 ml Et2O is added dropwise over a period of one hour. After 10 additional minutes, the layers are separated. The ether layer is extracted with 150 ml 0.25 N HCl, and then with 200 ml brine. Each aqueous layer is then backwashed successively with 100 ml Et2O. The combined Et2O layers are dried over anhydrous MgSO4, filtered, and concentrated under a N2 stream. The crystalline residue is slurried in a small amount of ether, filtered, and the pale yellow crystals are dried under high vacuum to give 4.7 g. - nitrobenzyloxycarbonylaminoethanethiol (65% yield). NMR (CDC13): 8.18 (d, J=8Hz, aromatic protons ortho to nitro), 7.47 (d, J=8Hz, aromatic protons meta to nitro), 5.27 (-NH-), 5.20 (s, ¯C¯2-NH-), 2.67 (m, -CH2-5H), 1.35 (t, J=8.5Hz, -SH) in ppm downfield from TMS. IR (CHC13 solution): carbonyl- 1725 cm . M.S.: molecular ion-256, (M-47) at 209, (M-136) at 120, CH2pNO2 at 136. EXAMPLE 17 Preparation of (5R,6S) p-Nitrobenzyl 3-[2-(p-nitrobenzyloxycarbonyl)amino ethylthio]-6-[(R)-1-hydroxyethyl]-1-azabicyclo [3,2,0]-hept-2-en-7-one=2=carboxylate EMI43.1 (5R,5S) p-Nitrobenzyl 6-[(R)1-hydroxyethyl]-1-azabicyclo [3,2,0]heptan-3,7-dione-2-carboxylate (51 mg, 0.14' mmol) is dissolved in acetonitrile (3 ml) an the resulting solution is cooled to 0 C. Diisopropylethylamine (22 mg, 0.17 mmol) s added by syringe and the resulting solution is stirred at 0 C for 1 rninute prior to the addition of z solution of freshly recrystallized p-toluene sulfonic anhydride (51 mg., 0.156 mmol) in dry acetonitrile (1 ml). The resuiting solution is stirred at 0 C for 1 hour to provide (SR,6Sjp-nitrobenzyl 3-(p-toluenesulfonyloxy)-6 [(R)-1-hydroxyethyl]-1-azabicyclo[3.2.0]hept=2-en-7-one2-carboxylate, then cooled to -250C: Diisopropylethylamine (80.5 mg, 0.624 mmol) is added b syringe followed shortly thereafter by a solution of N-p=-nitrobenzyloxycarbonylcysteamine (40 mg. 0.156 mmol) in 1 ml of dry acetonitrile. The reaction mixture is then stored in a refrigerater for 70 hr. The mixture is diluted with 25 ml of ethyl acetate washed with brine and dried over magnesium sulfate. Solvents are removed in vacuo to yield a yellow oil which is chromatographed on a silica gel plate (ethyl acetate, Rf=0.4) to yield (SR, 6S) p-nitrobenzyl3-[2-(p-nitrobenzyloxycarbonyl)amino ethylthio]-6-[(R)-1hydroxyethyl]-1-azabicyclo [3,2,0]-hept-2-en-7=dione2-carboxylate as a yellow solid, m.p. 167-1690C. IR(Nujol mull) 1773 and 1690 cm 1; n.m.r. (CDCl3)#7.54-8.26(overlapping ABq,4), #5.40(ABq,2), #5.22(s,2), #4.27(m,2), #3.47 (m), # 3.23(dd,1) #3.14 (dd,1) #3.40(dd,1), #3.04(m,2) #1.37(d,3) EXAMPLE 18 Preparation of Thienamycin EMI44.1 A mixture of N-p-nitrobenzyloxycarbonyl thienamycin pnitrobenzyl ester (10mg, 0.017 mmol) and 10% Pd/C-Bolhofer type in tetrahydrofuran (2ml), 0.10 dipotassium hydrogen phosphate solution (1.4 ml) and 2-propanol (0.2ml) is hydrogenated at 40 psi on the Parr shaker for-30 minutes. The mixture is then filtered and the catalyst is washed with water (3x3ml). The combined filtrate and washings are extracted with ethyl acetateethyl ether then concentrated to ¯ml and lyophilized. The resulting white powder is identical to natural thienamycin in all respects. EXAMPLE 19 Preparation of Benzyl (4-S) -azetidin-2-one-4-carboxylate EMI45.1 A mixture of dibenzyl (S)-aspartate p-toluenesulfonic acid salt (48.6g, 3.1 mole), diethylether (300ml), water (100ml), and saturated aqueous potassium carbonate (3'Omi) is shaken vigorously. The layers are separated and tiie aqueous portion is extracted with more ether (2x100ml). The combined ethereal extracts are washed with brine, dried with magnesium sulfa-.e, filtered, and evaporated under vacuum to afford dibenzyl (S)aspartate (31.5g) as a water white liquid. The dibenzyl (S)-aspartate in anhydrous diethyl ether (200ml) is cooled in an ice bath and stirred under a nitrogen atmosphere while trimethylchlorosilane (12.7ml, O.lmole) and triethylamine (14.Oml, 0.1 mole) are added successively over a few minutes. The cooling bath is removed and the mixture is stirred at room temperature for 2 hours. The mixture is then filtered under a blanket of nitrogen into a three-neck, one-liter, round bottom flask fitted with a sintered glass funnel, vacuum-nitrogen inlet, and a mechanical stirrer. Additional anhydrous ether (2x50ml) is used to wash the precipitate of tri ethylammonium hydrochloride. The funnel containing the precipitate is replaced by a dropping funnel and the etheral filtrate of dibenzyl (4S)-N-trimethyl silyl-aspartate is cooled in an ice bath and stirred under a nitrogen atmosphere while 2.1M t-butyl magnesium chloride in ether (48 ml, 0.1 mole) is added drop wise over 9 minutes. A gummy precipitate forms during the addition. The cooling bath is then removed and the mixture is allowed to stand at room temperature overnight. The mixture is cooled in an ice-bath and stirred vigorously while ammonium chloride saturated 2N hydrochloric acid (100 ml) is added over a few minutes. After stirring vigorously several more minutes, the mixture is diluted with water (100 ml) and ethyl acetate (100 ml) and the layers are separated. The aqueous portion is extracted with ethyl acetate (2x100ml). The combined organic solution is washed with water (100ml), 5% aqueous sodium bicarbonate (100ml), and brine (100ml), dried with magnesium sulfate, filtered, and evaporated under vacuum to a yellow semi-solid. Crystallization of this material from methylene chloride (100'ml)-petroleum ether (300 ml) provides the azetidinone product (8.2g) as an off-white powder. The mother liquors are evaporated and the residue crystallized from diethyl ether to afford additional product (2.5g) as a pale yellow product. The two crops are combined and recrystallized from methylene chloride to yield benzyl (4S)-azetidin-2-one-4-carboxylate (9.5g) as nearly colorless crystals: mp 139-141 ; [&alpha;]D= -40,50 (C2.0 in CHCl3); IR(CHC13) 3425, 1778, 1746cm 1; 1 NMR (CDC13) C3,00 (ddd, H-3ss), 3.35(ddd,H-3 ), 4.20(dd,H-4), 5;22(s,CH;), 6.48(m,NH), 7.35(s,phenyl); mass spectrum m/e 205(M ), 163, 91, 70, 43. EXAMPLE 2Q (4S)-1-(t-butyldimethylsilyl)-4-[2,2-(trimethylenedithia)-2-trimethylsilylethyl]-azetidin-2-one EMI47.1 A solution of 2-trimethylsilyl-1,3-dithiane (3.78g, 19.69 mmole) in anhydrous tetrahydrofuran (25 ml) at 0 C is stirred under nitrogen while n-butyllithium in hexane (20.67 mmol) is added dropwise. The resulting solution is stirred for 15 min. at 0 C then cooled to -780C (dry ice-acetone). A solution of (4S)-1-(t-butyldimethylsilyl)-4-iodimethylazetidin2-one (6.40g, 19.69 mmol) in 20 ml of anhydrous tetrahydrofuran is added slowly by syringe over ca. 5 min. The resulting solution is stirred at -780C for 1 hr., then quenched by the addition of saturated aqueous ammonium chloride solution (10 ml) and allowed to warm to room temperature (220C). The mixture is poured into a separatory funnel containing ethylether (200 ml) and water (100 ml). The organic phase is separated, washed with brine and dried over anhydrous magnesium sulfate. The solvent is removed in vacuo to yield a yellow oil. This material is filtered through a short silica gel column (25% ether in petroleum ether) to give 6.15g (80%) of (4S)-l-(t-butyldimethylsilyl)-4-[2,2-(trimethylenedithia)-2-trimethysilylethyl]-azetidin-2-one as a white solid, m.p. 71-73 C. n.n.r. (CDCl3) #3.9 (1H, m, H-5), 2.2-3.6 (8H, overlapping m) ,2.0(2H, m, SCH2CH2CH2S), @ 0.99 (9H, S, # Si), @0.23 (15H, br.S, (CH3)2Si & (CH3)3Si). IR (CHC13) 2930, 2855, 1723 cm-1. EXAMPLE 21 (3,R,S,4R)-l-(t-Butyldimethylsilyl)-3-[(R,S)-l- hydroxyethyl] 4-[2,2-(trimethylenedithia)-2- trimethylsilylethyl] -azetidin-2-one EMI49.1 A solution of diisopropylamine (10.5 mmol) in anhydrous tetrahydrofuran (40ml) is cooled to -780C (dry ice-acetone) and stirred under nitrogen atmosphere while n-butyllithium in hexane (10.5 mmol) is added slowly by syringe. After 15 min., a solution of (4S)-l-(t-butyldimethylsilyl) -4-[2,2-(tri- methylenedithia)-2-trimethylsilyl ethyl]-azetidin- 2-one (10.0 mmol) in anhydrous tetrahydrofuran (12ml) is added slowly by syringe. The resulting solution is stirred at -780C for 20 min. prior to the addition of acetaldehyde (30.0 mmol). After an additional 10 min. at -780C the reaction is quenched by the addition of saturated aqueous ammonium chloride solution (10 ml) and allowed to warm to room temperature. The reaction mixture is diluted with ethyl acetate (150 ml) and washed with 2.5N hydrochloric acid solution (50 ml), water (50 ml) and brine (50ml) and dried over magnesium sulfate. Removal of solvents in vacuo gives a white solid (4.6g) which is chromatographed on 250g of silica gel (1:1, ether: petroleum ether) to give four main product fractions with a total weight of 4.185g (96.7%). Fraction No. l-Rf=0.62, 85mg. Fraction No. 2 Ref=0.43, 1.95g (45%), (3S,4R)-l-(t-butyldimethyl-silyl) 3-r(s)-l-hydroxyethyl]-4-[2r2-(trimethylenedithia]-2-tri methylsilylethyl]-azetidin-2-one. Fraction No. 3-Rf = 0.34, 150 mg. mixture. Fract n No. 4-Rf=0.28, 2.0g (46%), (3S, 4R)-1-(tibutyldimetnylsilyl)-3-[(R)-1hydroxyethyl]-4-[2,2-(trimethylenedithia)-2-trimethylsilylethyl]-azetidin-2-one. EXAMPLE 22 (3S, 4R)-1-(t-Butyldimethylsilyl)-3-(1-oxoethyl)-4 [2,2 -(trimethylenedithia) -2-trimethylsilylethyl] - zzetidin-2-one Step A: EMI51.1 A solution of diisopropylamine (6.0 mmol) in anhydrous tetrahydrofuran (25 ml) is cooled to -780C (dry ice-acetone) and stirred under a nitrogen atmosphere while n-butyllithium in hexane (6.0 mmol) is added by syringe. After 15 min., a solution of (4S)-1-(t-butyldimethylsilyl)-4-[2,2-(trimethylenedithia)2-trimethylsilylethyl]-azetidin-2-one (3.0 mmol) in anhydrous tetrahydrofuran (3 ml) is added dropwise by syringe. The resulting sdbtion is stirred at -78 C for 30 min., then added through a Teflon tube to a mixture of N-acetylimidazole (6.0 mmol) and anhydrous tetrahydrofuran (25 ml) at -780C. The resulting yellow reaction mixture is stirred at -780C for 10 min., then quenched by addition of saturated aqueous ammonium chloride solution. The reaction mixture is poured into ether (200 ml) and extracted with 2.5N hydrochloric acid solution(50 ml), water (50 ml) and brine and dried over magnesium sulfate. Removal of solvents in vacuo gives a yellow oil which is chromatographed on silica gel tether-petroleum ether) (1:2) to yield (3S,4R)-l-(t-butyl- dimethylsilyl)-3-(1-oxoethyl)-4-[2,2-(trimethylenedithia)2-trimethysilylethyl]-azetidin-2-one. Step B: EMI52.1 Trifluoroacetic anhydride (6.0 mmol) is added by syringe to a solution of dimethylsulfoxide (8.0 mmol) in anhydrous methylene chloride (10 ml) at -780C. The resulting mixture is stirred at -78 C for 20 min., during which time a white precipitate forms. A solution of (3RS, 4R)-1-(t-butyldimethylsilyl)-3-(RS-1 hydroxyethyl) -4- [2,2- (trimethylenedithia) -2-trimethyl- silylethyl]-azetidin-2-one (4.0 mmol) in anhydrous methylene chloride (10 ml) is added by Syringe and the resulting mixture is stirred at -780C for 40 min. Triethylamine (11.2 mmole) is added by syringe and the cooling bath is removed. After 1 hr. the reaction mixture is diluted with CH2C12 (100 ml) and washed with 2.5N hydrochloric acid solution (50 ml), water (50 ml) and brine and dried over magnesium sulfate. Purification as above yields (3S, 4R)-l-(t-butyldimethylsilyl)-3- (1-oxoethyl)-4-[2,2-trimethylenedithia)-2-trimethylsilylethyl]-azetidin-2-one. n.m.r. (CDC13) 4.23 (1H, BrS, H-6), 64.2 (1H, m, H-5),j2.1-3.2 (6H, m), 2.27 (3H, S, CH3-C=O), #2.0 (2H, m, SCH2CH2CH2S), #0.96 (9H, S,+Si), # 0.25 (15H, br.S (CH2)2Si & tCE3)3Si). EXAMPLE 23 (3S, 4R)-1-(t-Butyldimethylsilyl)-3-[(R)-1-hydroxy ethyl]-4-[2,2-(trimethylenedithia-2-trimethylsilyl- ethyl]azetidin-2-one EMI53.1 K-Selectride (potassium tri-sec-butylborohydride) (4.8 mmol) in a solution of tetrahydrofuran is added dropwise by syring to a mixture of (3S, 4R)-1- (t-butyldimethylsilyl3-3-(1-oxoethyl)-4-[2,2-(trimethylene- dithia)-2-trimethylsilylethyl]-azetidin-2-one (2.0 mmol) and potassium iodide (2.0 mmol) in anhydrous ether (20 ml) at room temperature. The resulting mixture is stirred at room temperature for 2.5 hr., then quenched by addition of glacial acetic acid (9.6 mmol). The resulting mixture is diluted with ethyl acetate (50 ml) and filtered through celite. The solvents are removed in vacuo to give an oil which is chromatographed on silica gel (1:1, ether: petroleum ether) to give (3S,4R)-1- (t-butyldimethylsilyl)-3-[(R)-1-hydroxyethyl]-4-[2,2 (trimethylenedithia)-2-trimethylsilylethyl]-azetidin-2one as a white solid, n.m.r. (CDC13+D20) #4.23 (1H, dq. J=7.5,7,H-9)#2.78(1H, ddd, J=7.5, 3, 2.2, H-5) # 3.18 (1H, dd, 7.5, 2.2, H-6¯, #2.5-3.0 (4H, m, -SCH2CH2CH2S- #2.35 (2H, m, - CH2 + S¯, S2.0 (2H, m, SCH2CH2CH2S) 51.33 (3H, d, J=7, CH3-), # 0.98 (9H, S, + Si) # 0.26 (15H, br.S, (CH3)2 Si + (CH3)3Si). (3S,420-1-(t-Butyldimethylsilyl)-3-[(R)-l-hydroxyethyl]- 4-(2-oxo-2-trimethylsilylethyl)-azetidin-2-one EMI54.1 A mixture of mercuric oxide (.6.93 mmol),mercuric chloride (10.2 mmol) and (3S,4R -l-(t-butyldimethylsilyl)-3-[(R) - 1-hydroxyethyl]-4-[2,2-(trimethylenedithia)-2-trimethylsilylethyl]-azetidin-2-one (4.62 mmol) in 5% aqueous methanol (25 ml) is heated at reflux for 45 min. During this time, the color of reaction mixture changes from orange to off-white. The mixture is cooled and filtered and the filter cake is washed several times with methanol. The combined filtrate and washings are concentrated to 5 5 ml in vacuo, then diluted with ethyl acetate (100 ml) and washed with saturated aqueous ammonium chloride solution (2 x 50 ml) and brine. The organic phase is dried over magnesium sulfate and concentrated in vacuo to yield a pale yellow oil. This material is chromatographed on silica gel (ether) to yield (3S, 4R)- 1-(t-butyldimethylsilyl)-3-[(R)-1-hydroxyethyl]-4 (2-oxo-2-trimethylsilylethyl)-azetidin-2-one, 1.38g (87%), as a white solid, m.p. 82-840C. n.m.r. (CDC13-D20) #3.6 - 4.3 (2H, m, H-5, H-8) #3,12 (2H, center of d of AB, J= 18, 4, 8.5, -CH2-C-) S 2.7 (1H, dd, J= 7.5,2, H-6), #1.27 (3H, d, J=6,5, CH3-) # 0.99 (9H,s,+Si), #0.3 (15H, br.S, (CH3)3 Si & (CH3)2Si). I.R. (CHCl3) 3450, 2930, 2855,1737, 1635 cm EXAMPLE 24 EXAMPLE 25 (3S,4R)-1-(t-Butyldimethylsilyl)-3-[(R)-1-hydroxyethyl]4-carboxymethyl-azetidin-2-one EMI55.1 m-Chloroperbenzoic acid (1.00 mmol) is added to a solution of (3S,4R)-l-(t-butyldimethylsilyl-3-[(R)- 1-hydroxyethyl]-4-(2-oxo-2-trimethylsilylethyl)azetidin-2-one (1.00 mmol) in chloroform (4 ml). The resulting solution is heated at reflux for 4 hr, then cooled, concentrated in vacuo, and the residue chromatographed on silica gel (2% glacial acetic acid in methylene chloride). (3S, 4R)-1-(t-butyldimethylsilyl)- 3-[(R)-l-hydroxyethyl]-4-carboxymethyl-azetidin-2-one, 238 mg (83%) is isolated as a colorless solid, Rf = 0.25. n.m.r. (CDCl3 & D20) & .6 - 4.3 (2H, m, H-5, H-8), #2.98 (1H, dd, J=7, 2.1 H-6), #2.7 (2H,d of ABq)-CH2(CO2H), # 1.29 (3H, d, J=6, CH3-) s 0.95 (9H, S, Si+) , 0.25 (6H, S, (Ch3)2-Si). EXAMPLE 26 (3S, 4R)-1-(t-Butyldimethylsilyl)-3-[(R)-1hydroxyethyl]-4-(3-p-nitrobenzyloxycarbonyl-2oxopropyl)-azetidin-2-one EMI56.1 l,l'-Carbonyldimidazole (.1.10 mmol) is added in one portion to a solution of (3S, 4R)-1- (t-butyldimethyl- silyl-3- [(R) -l-hydroxyethyll -4-carboxymethyl-azetidin- 2-one C1.0 mmol2 in anhydrous tetrahydrofuran (5 ml) at room temperature. The resulting solution is stirred at room temperature for 6 hours. In a second flask, magnesium ethoxide (5 mmol) is added in one portion to a solution of the mono-p-nitrobenzyl ester of malonic acid (10 mmol) in anhydrous tetrahydrofuran (25 ml). The resulting mixture is stirred at room temperature for 1 hr, then the tetrahydrofuran is removed at the pump and the gummy residue is triturated with ether to yield the magnesium salt as an off-white solid.(l.l mmol) of this magnesium salt is then added to the first reaction flask and the resulting mixture is stirred at room temperature for 18 hrs. The reaction mixture is then poured into 50 ml of ether, washed with 0.5N hydrochloric acid solution (20 ml), water (20 ml), saturated aqueous sodium bicarbonate solution (20 ml), brine and dried over magnesium sulfate. Removal of solvents in vacuo gives an oil which is chromatographed on silica gel (ether) to yield (3S, 4R)-1-(t-butyldimethylsilyl)-3- [(R)-1-hydroxyethyl]-4-(3-p-nitrobenzyloxycarbonyl-2oxopropyl)-azetidin-2-one. n.m.r. (CDCl3 - H2O) @ 8.24, 8.10, 7.52, 7.38(2H, AB, aromatic), @ 5.26 (2H, S, -CH2-Ar), @@3.5-4.2 (2H, m, H-5, H-8) , @2.6-3.3 (3H, m, H-6, -CH2-C-, @ 1.3 (3H, d, J-6.6, CH3-) @ 0.98 (9H, S,+Si-) & 0.25 (6H, S, (CH3)2Si@) EXAMPLE 27 (3S,4R)-3-[(R)-l-hydroxyethyl]-4-(3-p-nitrobenzylOxy- carbonyl-2-oxopropyl)-azetidin-2-one EMI58.1 A solution of (3S, 4R)-l-(t-butyldimethylsilyl)-3- [(R)-l-hydroxyethyl]-4-(3-p-nitrobenzyloxyzarbonyl-2- oxopropyl)-azetidin-2-one (1.0 mmol) in 20 ml of 9:1 (v/v) methanol-water is cooled to OOC. Concentrated hydrochloric acid (0.34 ml) is added and the resulting solution is stirred at OOC for 15 min., then allowed to warm to room temperature. After 2.5 hrs, at room temperature the reaction mixture is diluted with ethyl acetate (25 ml), washed with water (10 ml) and. brine, dried over magnesium sulfate and concentrated in vacuo to yield (3S, 4R)-3-[(R)-l-hydroxyethyl]-4- (.3-p-nitrobenzyloxycarbonyl-2-oxopropyl) -azetidin-2-one.

Claims: WHAT IS CLAIMED IS 1. A compound selected from the group consisting of: EMI59.1 wherein R2 and R3 are independently selected from: lower alkylhaving 1-6 carbon atoms, phenyl, benzyl, methoxybenzyl, or trityl; R' is a readily removable protecting group or hydrogen; R8 is lower alkyl having 1-6 carbon atoms, or phenyl, or R2 and R3 together form EMI59.2 2. A compound according to Claim 1 , wherein: R' is triloweralkyl silyl having from 3-12 carbon atoms; R8 is alkyl having 1-3 carbon atoms, or phenyl; and R2 and R3 are: EMI59.3 or alkyl having 1-3 carbon atoms each. 3. A process for preparing EMI60.1 comprising: oxidizing: EMI60.2 to form: EMI60.3 followed by treating with R7O2CCH2CO@2 to yield : EMI60.4 wherein R7 and R' are readily removable protecting groups. 4. A process for preparing EMI61.1 comprising: oxidizing: EMI61.2 to form: EMI61.3 followed by treating with (R7CO2CCH2CO2)2Mg. EMI61.4 wherein R7 and R' are readily removable protecting groups. 5. A compound having the structure: EMI62.1 wherein R is a readily removable blocking group. 6. A compound according to Claim 5 wherein: R is trialkylsilyl wherein the alkyl moieties have 1-6 carbon atoms each. 7. A compound. according to Claim 6 wherein R is (t-butyl) dimethylsilyl. Claims for Austria 1. A process for preparing EMI63.1 comprising: oxidizing: EMI63.2 to form: EMI63.3 followed by treating with R7O2CCH2CO@2to yield : EMI63.4 wherein R7 and R' are readily removable protecting groups. 2. A process for preparing EMI64.1 comprising: oxidizing: EMI64.2 to form: EMI64.3 followed by treating with (R7Co2CCH2C02) 2Mg. EMI64.4 wherein R7 and R" are readily removable protecting groups.

Inventors: CHRISTENSEN, BURTON G., RATCLIFFE, RONALD W., SALZMANN, THOMAS N.
Applicants: MERCK & CO. INC.
Application year: 1980
Main classification: C07D205
IPC codes: C07D499, A61K31, C07D205, C07F7, A61P31, C07D477