The chemistry of 4-mercaptoazetidin-2-ones. Part 2. Synthesis of bisnorpenicillins

Abstract

Reaction of the 4-mercaptoazetidinone (2) with benzyl 2-bromoacrylate gave the C-3-epimeric bisnorpenicillin esters (6b) and (7b). Standard procedures were used to convert the ester (6b) into bisnorpenicillin V (3) and bisnorampicillin (15). By contrast (2), with either (E)- or (Z)-benzyl 2-bromocrotonates, gave the penam esters (20) and (21) and not the expected benzyl esters of the norpenicillanic acids (16a) and (16b). This reaction was shown to proceed via the olefin (22).