Asymmetric Autotandem Palladium Catalysis for ,-Unsaturated Lactones: Merging Olefin and Ester Hydrogenation

Autotandem catalysis (ATC) is fascinating since a single catalyst can promote tandem reactions involving two or more mechanisms in a single reactor and is a highly desirable approach to realize multifarious transformations in organic synthetic chemistry. Herein, a palladium-catalyzed asymmetric autotandem hydrogenation of alpha,beta-unsaturated lactones is disclosed, providing chiral saturated alcohols. In this reaction, the C=C bond in alpha,beta-unsaturated lactones was first hydrogenated to give the dihydrocoumarins with high enantioselectivity, followed by hydrogenation of the ester group with the same catalytic system. Notably, after decreasing the reaction temperature, hydrogenation of the single C=C bond proceeded smoothly, delivering the dihydrocoumarin products with high yield and enantioselectivity. Control experiments and density functional theory calculations were carried out to elucidate the cause of this unusual asymmetric autotandem hydrogenation. Notably, the homogeneous palladium catalyst was successfully applied in the hydrogenation of esters under neutral conditions.