Iridium-Catalyzed Asymmetric Transfer Hydrogenation of 1-Aryl-1-alkylethenes with Ethanol

Asymmetrictransfer hydrogenation of 1-aryl-1-alkylethenes withethanol was developed with a chiral (PCN)Ir complex as the precatalyst,featuring high enantioselectivities, good functional group tolerance,and operational simplicity. The method is further applied to formalintramolecular asymmetric transfer hydrogenation of alkenols withoutan external H-donor, producing a tertiary stereocenter and remoteketone group simultaneously. The utility of the catalytic system washighlighted by gram scale synthesis and the synthesis of the key precursorof (R)-xanthorrhizol.