Preparation of (5R)-penem derivatives

摘要

(5R)-penem derivatives of the general formula I (R1=H or an organic group, R2=H or a carboxy protecting group and Y=H, halogen or an organic group) are prepared by oxidising 2-thiacephem derivatives of the general formula II (R1, R2 and Y as above defined) by means of organic peracids, and submitting the resultant corresponding 1,1-dioxide of formula III to a desulphurative ring contraction with expulsion of SO2.