Regio- and diastereoselective synthesis of 3,4-dihydro-2H-benzo [4,5]imidazo[2,1-b] [1,3]thiazine derivatives via DBU-catalyzed [3+3] annulation of MBH carbonates with 2-mercaptobenzimidazoles

Abstract

Benzimidazo [2,1-b] [1,3]thiazines as an important class of N,S-containing heterocyclic compounds are usually present in molecules with diverse biological and pharmaceutical activities. An efficient DBU-catalyzed [3 + 3] annulation reaction between Morita-Baylis-Hillman carbonates and 2-mercaptobenzimidazoles has been developed. Under mild reaction conditions, a wide range of functionalized 3,4-dihydro-2H-benzo[4,5]imidazo [2,1-b][1,3]thiazines possessing two contiguous stereogenic centers on thiazine ring were prepared in moderate to excellent yields (48–93%) and diastereoselectivities (59:41 to >95:5).