合成路线1

A new procedure based on the counterattack stategy was further developed. Azetidinonepropionic acid (XXXV) was available from acetoxy azetidinone (XXXIII) by coupling with benzoxazinone (XXXIV). After protection of (XXXV) with tert-butyldimethylsilyl chloride, alkylation with allyl bromoacetate yielded (XXXVI). DCC-mediated condensation of (XXXVI) with mercaptopyrrolidine (IV) produced thioester (XXXVII). Dieckman-type cyclization of (XXXVII) upon treatment with sodium bis(trimethylsilyl)amide produced carbapenem (XXXVIII) together with mercaptopyrrolidine (XXXIX). Treatment of the crude reaction mixture with chlorotrimethylsilane and subsequent addition of diphenylphosphoryl chloride generated the vinyl phosphate (XL) and the silylated mercaptopyrrolidine (XLI). The counterattack of the thiolate anion, liberated by desilylation of (XLI) with tetrabutylammonium fluoride, to the vinyl phosphate (XL) yielded the desired thioether (XLII). The hydroxyl protective group of (XLII) was removed by treatment with NH4F·HF to give (XLIII), and the allyl ester group of (XLIII) was further cleaved by means of palladium diacetate, producing carboxylic acid (XLIV). Finally, alkylation of the carboxylate group of (XLIV) with iodomethyl isobutyrate (XVI) gave rise to the title compound.