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.