Concise assembly of highly substituted furan-fused 1,4-thiazepines and their Diels-Alder reactions with benzynes

A facile and highly efficient three-component reaction of thiazole or benzothiazole carbenes, disubstituted ketenes, and activated alkynes is disclosed. With this methodology, a polysubstituted ring system containing furo[2,3-c]thiazepine core can be constructed from simple and readily accessible starting materials in good yields. The scope and limitation of this transformation were investigated in detail by using various thiazole carbene, ketene, and alkyne components. Furthermore, the synthetic utilities of these unique polyheterocyclic compounds were demonstrated via their Diels-Alder reactions with benzynes to furnish thiazepine-fused 7-oxanorbornadiene derivatives in excellent yields.