Tunable Pd-Catalyzed Cyclization of Indole-2-carboxylic Acid Allenamides: Carboamination vs Microwave-Assisted Hydroamination

Abstract

A variety of 3-vinyl-substituted imidazo[1,5-a]indole derivatives were synthesized by intramolecular Pd-catalyzed cyclization of the title allenamides through either a domino carbopalladation/exo-cyclization process or a novel hydroamination reaction that proceeds smoothly under microwave irradiation. Both the observed pathways involve a π-allyl-palladium(II) complex arising from insertion of the allene group into a palladium(II) species, the latter being formed in situ by the intervention of an aryl iodide or of the N-H group. In both cases, the role of nucleophile is covered by the indole nitrogen.