Nuclear modification of clavulanic acid. Preparation of optically active 1-oxaceph-3-ems

Abstract

Lithium (Z)-(6R)-3-benzyloxycarbonyl-2-(2-methoxyethylidene)-1-oxaceph-3-em-4-carboxylate and lithium (Z)-(6R)-2-(2-methoxyethylidene)-1-pxaceph-3-em-4-carboxylate have been prepared from clavulanic acid by way of an intramolecular Wittig reaction. Also from clavulanic acid, methyl (Z)-(6R)-3-methoxy-2-(2-methoxyethylidene)-1-oxaceph-3-em-4-carboxylate has been synthesised by way of an intramolecular carbene-insertion reaction.