Gold‐Catalyzed Tandem Oxidation‐Migration of 3‐Propargyl Indoles: Synthesis of α‐Indol‐3‐yl α,β‐Unsaturated Carbonyls

Abstract

α-Indol-3-yl α,β-unsaturated carbonyl compounds are synthesized from 3-propargyl indoles, obtained by direct propargylation of indoles, via a gold-catalyzed tandem oxidation-1,2-indole migration reaction in the presence of pyridine N-oxides. Fine-tuning of the catalyst and oxidant enables the reaction of 3-propargyl indoles bearing different substituents. The order of oxidation and indole migration is determined by the terminal or internal nature of the alkyne moiety. In addition, the process can be coupled with additional reactions, allowing an increase in molecular complexity or the design of more elaborated tandem reactions. In this sense, indole derivatives bearing an alkenyl substituent at the alkyne position evolve through a gold-catalyzed tandem oxidation-1,2-indole migration-Nazarov cyclization producing α-indolyl cyclopentenones.