Zn(II)‐Catalyzed Asymmetric Transfer Hydrogenation of <i>γ</i>‐Indolyl <i>β</i>,<i>γ</i>‐Unsaturated <i>α</i>‐Keto Amides and <i>α</i>‐Keto Esters with Hantzsch Ester

Abstract Highly enantioselective transfer hydrogenation of γ ‐indolyl β , γ ‐unsaturated α ‐keto amides and α ‐keto esters with Hantzsch ester catalyzed by chiral zinc complex is reported. Using 5 mol% of Zn(OTf) 2 ‐imidazolidine‐pyrroloimidazolone pyridine as the catalyst, the C=C bond in γ ‐indolyl β , γ ‐unsaturated α ‐keto amides is selectively reduced, affording hydrogenation products in high yields (up to 99% yield) and excellent enantioselectivities (up to 99% ee). Using the same catalyst system, the C=O bond in α ‐keto esters is reduced, generating α ‐hydroxy esters in good results (up to 99% yield and 98% ee). A retro‐Michael pathway and subsequent transfer hydrogenation reaction are proposed for the explanation of the side products in the transfer hydrogenation of γ ‐indolyl β , γ ‐unsaturated α ‐keto amides.