Synthesis of t-butyl 2-(2-methoxycarbonyl-1-methylethylidene)penam-3-carboxylates; clavulanic acid analogues

Abstract

4-Acetonylthioazetidin-2-one (2) has been converted in three steps into t-butyl 2-acetylpenam-3-carboxylates (5) and (6). Wittig reaction on these produced t-butyl 2-(2-methoxycarbonyl-1-methylvinyl)penam-3-carboxylates (9) and (10), which were transformed by base catalysis into three racemic isomers [(11), (12), and (13)] of the title compound. Stereochemistry of the products was deduced by n.m.r. spectroscopy, including N.O.E. studies.