STUDIES ON RING-OPENING REACTIONS OF BETA-LACTAMS

Reaction of tricyclic azetidinones 1-5 (azetobenzoxazine, -thiazine, - thiazepine and -azepine derivatives) with trifluoroacetic acid led to bicyclic thioesters 6-13. There is evidence for an intermolecular reac tion, a possible mechanism is discussed. The structure of two represen tative thioesters (8 and 9) was elucidated by different NMR experiment s, complete assignments of H-1- and C-13-chemical shifts are given. Re action of the azetobenzoxazine 2 with sodium periodate and magnesium m onoperoxyphthalate led to the sulfoxide 18 and the sulfone 19, respect ively. (C) 1997 Elsevier Science Ltd.