One-Pot Copper-Catalyzed Cascade Bicyclization Strategy for Synthesis of 2-(1H-Indol-1-yl)-4,5-dihydrothiazoles and 2-(1H-Indol-1-yl)thiazol-5-yl Aryl Ketones with Molecular Oxygen as an Oxygen Source

An atom-economical method for synthesizing N-heterocyclic indoles from readily available o-alkynylphenyl isothiocyanates and propargylamine derivatives is reported. This method involves a copper-catalyzed cascade bicyclization process consisting of an intramolecular 5-exo-dig hydrothiolation reaction and an intramolecular hydroamination reaction and, depending on whether or not molecular oxygen is present, selectively affords Z-isomers of 2-(1H-indol-1-yl)-4,5-dihydrothiazoles or 2-(1H-indol-1-yl)thiazol-5-yl aryl ketones in satisfactory yields. Mechanistic studies indicate that molecular oxygen acts as the oxygen source for the ketone moiety in the products.