Formation and Trapping of Azafulvene Intermediates Derived from Manganese-Mediated Oxidative Malonate Coupling

Tetrahedron. 2016 Jun 30;72(26):3775-3780. doi: 10.1016/j.tet.2016.03.012. Epub 2016 Mar 4.

Abstract

The one-pot, three-component, coupling reaction of indoles/pyrroles, dimethyl malonate, and acetic acid was performed using Mn(III) acetate as an oxidant. In the presence of Mn(OAc)3, indole-2, and indole-3-carbonyl compounds were alkylated at the 3- and 2- positions, respectively, with subsequent oxidation and nucleophilic capture occurring at the newly formed benzylic carbon. In contrast, oxidation of 2- and 3-indole carboxylic acids afforded the corresponding 2-oxindol-3-ylidenes and 3-oxindol-2-ylidenes. The reaction conditions, scope, and mechanism are discussed herein.