Visible-Light-Promoted [3 + 2] Cyclization of Chalcones with 2-Mercaptobenzimidazoles: A Protocol for the Synthesis of Imidazo[2,1- b ]thiazoles.

A visible-light-promoted [3 + 2] cyclization between chalcones and 2-mercaptobenzoimidazoles for the construction of diverse imidazo[2,1- b ]thiazoles via an electron-donor-acceptor (EDA) complex has been developed. This novel aminothiolation can be realized under only visible light irradiation without the aid of external photocatalysts, transition metals, and oxidants. Mechanistic investigations have revealed that the thiol anions and chalcones form EDA complexes, providing a novel strategy for the synthesis of imidazo[2,1- b ]thiazoles.