A new process is described for the preparation of (5R)-penem derivatives of the general formula I: ##STR1## wherein R.sub.1 represents a hydrogen atom or an organic group; R.sub.2 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: ##STR2## wherein R.sub.1, R.sub.2 and Y have the meanings/given above is oxidized by means of organic peracids to the corresponding sulphone of the general formula III: ##STR3## which is subsequently submitted to a desulphurative ring contraction by extrusion of SO.sub.2 to give exclusively the desired (5R)-penem derivatives of the general formula I.
本文描述了一种制备通式I中的(5R)-青霉烷衍
生物的新工艺:##STR1## 其中R.sub.1代表氢原子或有机基团; R.sub.2代表氢原子或羧基保护基团,Y代表氢或卤素原子或有机基团。通式II的2-
硫代
头孢菌素衍
生物:##STR2## 其中R.sub.1、R.sub.2和Y具有上述含义,通过有机过氧酸氧化为相应的通式III砜:##STR3## 随后通过排出SO.sub.2进行脱
硫环收缩,仅生成所需的(5R)-青霉烷衍
生物通式I。