Organocatalytic Michael Addition of Indoles to α‐Substituted Enals by Using a Diazepane Carboxylate Catalyst

Abstract

The conjugate addition of indoles to α‐substituted enals is achieved by using a diazepane carboxylate catalyst under mild conditions (20 mol‐% catalyst, 20 mol‐% TFA, acetonitrile, –20 °C). The low basicity and high nucleophilicity of this catalyst overcomes the limitations of allylic 1,3 strain in the intermediate iminium ions, which is normally observed with secondary‐amine catalysts. Conjugate addition of a series of substituted indoles as well as electron‐rich aromatics with a variety of α‐substituted enals is demonstrated.