Access to benzo[ e ][1,3]thiazin-4-ones via PCy 3 -mediated annulations of benzo[ c ][1,2]dithiol-3-ones with iso(thio)cyanates

A novel organophosphine-mediated annulation reaction of benzo[ c ][1,2]dithiol-3-ones with iso(thio)cyanates to synthesise benzo[ e ][1,3]thiazin-4-one derivatives has been developed, which proceeds via an S atom to C–N unit exchange strategy.