IMINIUM CARBONIC-ACID DERIVATIVE SALTS .10. SYNTHESIS OF N,S-CONTAINING HETEROBICYCLES FROM N-PROTECTED 2-METHYLTHIO-1,3-THIAZINIUM AND 2-METHYLTHIOTHIAZOLIUM SALTS .2. REACTION OF N-PROTECTED 2-METHYLTHIO-1,3-THIAZINIUM AND 2-METHYLTHIOTHIAZOLIUM SALTS WITH VINYLOGOUS CH-ACIDICCOMPOUNDS

N-Boc-protected 2-methylthio-1,3-thiazinium 3 and 2-methylthiothiazoli um salts 4,7 obtained from the corresponding 1,3-thiazine-2-thiones an d thiazolidine-2-thiones by the action of methyl iodide or trimethylox onium tetrafluoroborate were reacted with vinylogous CH-acidic compoun ds forming ketene N,S-acetals 5,6,8,9. The protection group was remove d with trifluoroacetic acid whereupon the desired cyclisation to pyrid o[2,1-bl-1,3-thiazines 10 and thiazolo[3,2-b]pyridines 11,12 took plac e.