Copper-Promoted Cycloaddition of α-Methylenyl Isocyanides with Benzothiazoles: Tunable Access to Benzo[d]imidazothiazoles

A tunable route to both isomers of benzo[d]imidazothiazole has been developed through copper-promoted cycloaddition of alpha-methylenyl isocyanides with benzothiazoles. When the C2 position of benzothiazole is linked to a C-H or C-C bond, benzo[d]imidazo[2,1-b]thiazoles are obtained through a novel rearrangement via C-S bond cleavage and formation of a new C-S bond. When 2-chloro- or 2-bromobenzothiazoles are used under the same reaction conditions, the isomeric benzo[d]imidazo [5,1-b]thiazoles are formed selectively. These reactions proceed smoothly in moderate to excellent yields at room temperature, and a wide range of functional groups are tolerated.