Gold-Catalyzed Cyclization of Pyrrole-Tethered Allenynes for the Synthesis of 4-Acylindoles and Its Application to the Ergot Alkaloid Scaffold

Gold-catalyzed cyclization of pyrrole-tethered allenynes produces 4-acylindoles, accompanied by oxidative benzene ring formation. This reaction would proceed via the activation of the allene by a gold catalyst, nucleophilic attack of the alkyne in a 6-endo-dig manner, and trapping of the resulting vinyl cation by an oxygen nucleophile. This methodology was successfully applied to construct the core structure of the ergot alkaloids.