Synthesis of 3,4-Benzo-1-oxacephem / Synthesis of 3,4-Benzo-1-oxacephem

The thioformimidate 4, which may be obtained by S-methylation of 5 reacts with chloroacetyl chloride/triethylamine to yield the trans-2-azetidinone 7. 7 is dehalogenated to 8. Removal of the protective group leads to 9, which undergoes ring closure by the action with mercuric chloride/ mercuric oxide. Chlorolysis of 8 and the subsequent reaction with hydrofluoric acid/acetonitrile yields 12. The treatment of 12 with silver tetrafluoroborate/silver oxide gives also the title compound 10