Rhodium-Catalyzed Highly Regio- and Enantioselective Reductive Cyclization of Alkyne-Tethered Cyclohexadienones

Rhodium-catalyzed asymmetric hydrogenation of alkyne-tethered cyclohexadienones enables highly regio- and enantioselective reductive cyclization to afford cis-hydrobenzofurans and cis-hydroindoles in high yields. Desymmetrization of 1,3-diyne-tethered cyclohexadienones was also explored, wherein the intramolecular coordination of a Rh complex with the cyclohexadienone ring induces exclusive regioselectivity. Mechanistic studies including hydrogen deuterium crossover experiments suggested that hydrogen activation is the rate-determining step for tandem reductive cyclization. Moreover, this highly practical and atom-economical transformation has tolerance to many functional groups with a broad range of substrate scope, allowing further transformations to expand the structural complexity of the bicyclic scaffolds.