合成路线1

The condensation of (3R,4R)-4-acetoxy-3-[1(R)-(tert-butyldimethylsilylioxy)ethyl)azetidin-2-one (I) with benzyl 2-bromopropionate (II) by means of diethylaluminum chloride in hexane - THF gives the isomeric mixture (III), (IIIa), which is separated by column chrornatography and the correct isomer (III) is treated with tert-butyldimethylsilyl chloride to yield the silylated azetidine (IV). The reductive debenzylation of (IV) with H2 over Pd/C in methanol affords the protected free acid (V), which is condensed with magnesium 4-nitrobenzylmalonate (VI) by means of carbonyldiimidazole (CDI) in hot acetonitrile to give the protected ketoester (VII). Partial hydrolysis of (VII) with HCl in methanol affords the free ketoester (VIII), which is treated with p-toluenesulfonylazide in acetonitrile yielding the diazo compound (IX). The cyclization of (IX) by means of rhodium acetate in refluxing toluene gives 6alpha-[1(R)-hydroxyethyl)-1beta-methyl-2-oxo-1-dethia-1-carba-2-penem-3-car boxylic acid 4-nitrobenzyl ester (X), which is condensed with diphenyl chlorophosphate (XI) by means of diisopropylethylamine in acetonitrile, yielding the enol ester (XII).