Aerobic Copper-Catalyzed Four-Component Reaction of O-Phenylenediamines, Isocyanides, and Selenium Powder for the Assembly of Benzo[4,5]imidazo[2,1-c][1,2,4]selenadiazol-3-imine Derivatives.

A convenient, four-component reaction of o-phenylenediamines, isocyanides, and selenium powder catalyzed by a natural abundant copper/air (O2) catalyst system has been developed, providing a highly step and atom economical protocol for the synthesis of benzo[4,5]imidazo[2,1-c][1,2,4]selenadiazol-3-imine derivatives with excellent yields and good functional group tolerance. This method enables the construction of an imidazo[2,1-c][1,2,4]selenadiazol ring, one N-Se bond, one C-Se bond, and three C-N bonds in a single step with only water as the byproduct. Preliminary mechanistic studies imply that the copper/air (O2)-catalyzed cyclization proceeds via a selenium-centered radical intermediate.