Reactions of thiazolium and benzothiazolium N-phenacylides with dimethyl acetylenedicarboxylate (DMAD) have been reexamined. The thiazolium N-phenacylides 5, generated in situ from 4-methyl-or 5-phenyl-3-phenacylthiazolium bromides 13 with triethylamine, reacted with DMAD in dry DMF to give the thiazole ring-opened products 15, in which two molecules of DMAD had been incorporated. The reactions when conducted ...
