Asymmetric Vinylogous Diels–Alder Reactions Catalyzed by a Chiral Phosphoric Acid

An unprecedented way to extend the synthetic utility of the Diels–Alder reaction to include a vinylogous reactivity space is described. A commercially available chiral phosphoric acid catalyst effectively activates cyclic 2,4-dienones towards a vinylogous [4+2] cycloaddition with 2-vinylindoles, which leads to stereochemically dense tetrahydrocarbazoles. The reaction proceeds with a high level of remote stereocontrol and exclusive chemoselectivity for the more distant double bond of the dienone.