The Copper-Catalyzed Reaction of 2-(1-Hydroxyprop-2-yn-1-yl)phenols with Sulfonyl Azides Leading to C3-Unsubstituted -Sulfonyl-2-iminocoumarins.

An operationally simple synthesis of -configured and C3-unsubstituted -sulfonyl-2-iminocoumarins (e.g., ) that proceeds under mild conditions is achieved by reacting 2-(1-hydroxyprop-2-yn-1-yl)phenols (e.g., ) with sulfonyl azides (e.g., ). The cascade process involved likely starts with a copper-catalyzed alkyne-azide cycloaddition (CuAAC) reaction. This is followed by ring-opening of the resulting metalated triazole (with accompanying loss of nitrogen), reaction of the ensuing ketenimine with the pendant phenolic hydroxyl group, and finally dehydration of the ()--(4-hydroxychroman-2-ylidene)sulfonamide so formed.