Three-component bis-heterocycliation for synthesis of 2-aminobenzo[4,5]thieno[3,2-d]thiazoles

A cooperative base system has been developed for the novel three component bis-heterocyclization of methylketoxime acetates. In a reaction complementary to previous thiazole and benzo[4,5]thieno[3,2-d]thiazole formation, the present protocol provides an effective entry to 2-aminobenzo[4,5]thieno[3,2-d]thiazoles. Mechanistically, the formation of trisulfur radical anion [S3]˙− and Willgerodt–Kindler-type sulfuration would be the key for this transformation.