Studies related to penicillins and cephalosporins. Part III. Oxidative rearrangement of a 4-mercaptoazetidin-2-one to a Δ4-isothiazolin-3-one

Abstract

4-(p-Methoxybenzylthio)-1-(1-methoxycarbonyl-2-methylprop-1-enyl)-3-phthalimidoazetidin-2-one (16) was obtained in the reaction of p-methoxybenzyl N-(1-methoxycarbonyl-2-methylprop-1-enyl)thioformimidate (14) with phthaloylglycyl chloride and triethylamine. Removal of the sulphur-protecting group in compound (16) gave the 4-mercapto-β-lactam (17), which underwent oxidative rearrangement to 2-(1-methoxycarbonyl-2-methylprop-1-enyl)-4-phthalimido-Δ⁴-isothiazolin-3-one (20) when treated with dimethyl sulphoxide.