PREPARATION OF 2-THIACEPHEMS

摘要

2-Thiacephems II (R1=H or an organic group, R2=H or a carboxy protecting group and Y=H, halogen or an organic group) are prepared from azetidinones IV (R1, R2 as above and Z represents various organic groups) by ozonolysis of the double bond, conversion of the hydroxy group to a halogen atom, an alkane sulphonyloxy group or an arene sulphonyloxy group, and cyclisation by reaction with a sulphide or hydrosulphide in the presence of a base to give II (Y=H). Halogenation, preferably after cyclisation, using N-bromosuccinimide or N-chlorosuccinimide in an inert organic solvent at 20-130 DEG C in the presence of a radical initiator and an acid scavenger, gives II (Y=halogen). The latter compounds may be converted to II (Y=organic group) by known reactions. The 2-thiacephems II are useful in the preparation of penems as described in Application No. 2131432, from which this Application is divided.