A Highly Efficient Copper(I)-Catalyzed Cascade Reaction of o-Alkenylphenyl Isothiocyanates with Isocyanides Leading to 5H-Benzo[d]imidazo[5,1-b][1,3]thiazines

The highly efficient copper(I)-catalyzed cascade reaction of (E)-3-(2-isothiocyanatophenyl)acrylates and (E)-3-(2-isothiocyanatophenyl)acrylonitriles with isocyanides was explored. The method provides an expedient route for the synthesis of 5H-benzo[d]imidazo[5,1-b][1,3]thiazines in good to excellent yields by using CuCl (10 mol-%) as the catalyst and K3PO4 (2.0 equiv.) as the base in THF at 70 degrees C. The reaction involves [3+2] cycloaddition and subsequent intramolecular C-S bond formation.