An Asymmetric Dehydrogenative Diels-Alder Reaction for the Synthesis of Chiral Tetrahydrocarbazole Derivatives.

An asymmetric dehydrogenative Diels-Alder reaction of 2-methyl-3-phenylmethylindoles and α,ß-unsaturated aldehydes has been established. The successful in situ generation of the indole ortho-quinodimethane intermediate and the iminium activation of enals are the keys to success, providing various tetrahydrocarbazole derivatives with up to >99% ee.