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.

Automated summary

Asymmetric transfer hydrogenation of 1-aryl-1-alkylethenes with ethanol using a chiral (PCN)Ir complex as the precatalyst has been developed, demonstrating high enantioselectivities, good functional group tolerance, and operational simplicity. This method is also applied to formal intramolecular asymmetric transfer hydrogenation of alkenols without an external H-donor, allowing for the production of a tertiary stereocenter and remote ketone group simultaneously. The utility of the catalytic system is highlighted by gram scale synthesis and the synthesis of the key precursor of (R)-xanthorrhizol.