Studies on Heteropentalenes. II. Cycloaddition of Imidazothiazoles, Thiazolobenzimidazole, and Imidazobenzothiazole with a Reactive Acetylenic Ester

Article abstract of DOI:10.1246/bcsj.53.3308

Cycloaddition of imidazo<2,1-b>thiazoles with dialkyl acetylenedicarboxylate follows dual courses depending on the polarity of the solvent, affording pyrrolo<2,1-b>thiazoles in an aprotic nonpolar solvent, or imidazo<1,2-a>pyridines and imidazo<3,4-a>pyridines, together with thiophenes, in an aprotic polar solvent.Thiazolo<3,2-a>benzimidazole and imidazo<2,1-b>benzothiazole were also found to react with the acetylenedicarboxylate to give pyrido<1,2-a>benzimidazole and pyrrolo<2,1-a>benzothiazole, respectively.The reactions would be accounted for in light of the Diels -Alder reaction in an aprotic nonpolar solvent and the 1,4-dipolar cycloaddition in an aprotic polar solvent.