Gold-Catalyzed Selective 6-<i>exo-dig</i> and 7-<i>endo-dig</i> Cyclizations of Alkyn-Tethered Indoles To Prepare Rutaecarpine Derivatives

Abstract

An efficient method to synthesize rutaecarpine derivatives via the gold-catalyzed selective cyclization of alkyn-tethered indoles under mild conditions is described. The alkyn-tethered indole can undergo 6-exo-dig cyclization by oxidation and sequential gold catalysis, while it goes through 7-endo-dig cyclization by gold catalysis and sequential oxidation. Substrate scope studies reveal that the selectivity of cyclization was controlled by the substrates with sp³ and sp² hybridization of carbon at the 2 position in quinazolinone. Furthermore, the rutaecarpine scaffold was prepared in 67% yield at gram scale easily in four steps from isatoic anhydride.