The chemistry of 4-mercaptoazetidin-2-ones. Part 4. Synthesis of cyclopropanespiro-2-bisnorpenicillanic acids

Reaction of the 4-mercaptoazetidin-2-one (6) with benzyl 2-bromocyclopropylideneacetate (7) gave the C-3 epimeric cyclopropanespiro-2-bisnorpenicillanates (9) and (10). Standard procedures were used to convert the 3S-epimer into the ampicillin analogue (15). Hydrogenolysis of the esters (9) and (15) gave the cyclopropane spiro-2-bisnorpenicillanic acids (13) and (16) both of which had antibacterial properties similar to those of the corresponding penicillins.