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. Further and further: A vinylogous Diels–Alder reaction that is catalyzed by a commercially available chiral phosphoric acid has been developed. A range of structurally diverse complex tetrahydrocarbazoles were obtained in high chemical yields and with excellent stereoselectivity. It was thus demonstrated that the synthetic utility of the Diels–Alder reaction can be extended to include a vinylogous reactivity space.