2-THIACEPHEMS AND (5R) PENEMS DERIVATIVES

摘要

A new process is described for the preparation of (5R)-penem derivatives of the general formula I: I wherein R1 represents a hydrogen atom or an organic group; R2 represents a hydrogen atom or a carboxy protecting group and Y represents a hydrogen or halogen atom or an organic group. A 2-thiacephem derivative of the general formula II: II wherein R1, R2 and Y have the meanings/given above is oxidized by means of organic peracids to the corresponding sulphone of the general formula III: III which is subsequently submitted to a desulphurative ring contraction by extrusion of SO2 to give exclusively the desired (5R)-penem derivatives of the general formula I.