A Frustrated Lewis Pair Catalyzed Asymmetric Transfer Hydrogenation of Imines Using Ammonia Borane

Inspired by the zwitterion species generated from the splitting of H₂ by frustrated Lewis pairs, we put forward a novel frustrated Lewis pair by the combination of H^δ‑ and H^δ+ incorporated Lewis acid and base together. Piers’ borane and chiral <i>tert</i>-butylsulfinamide were chosen as the FLP, and a metal-free asymmetric transfer hydrogenation of imines was realized with high enantioselectivities. Significantly, with ammonia borane as hydrogen source, a catalytic asymmetric reaction using 10 mol % of Piers’ borane, chiral <i>tert</i>-butylsulfinamide, and pyridine additive, has been successfully achieved to furnish optically active amines in 78–99% yields with 84–95% ee’s. Experimental and theoretical mechanistic studies reveal an interesting 8-membered ring hydrogen transfer transition state and an expected regeneration of reactive species with ammonia borane. Accordingly, a plausible catalytic pathway for this reaction is depicted

A Frustrated Lewis Pair Catalyzed Asymmetric Transfer Hydrogenation of Imines Using Ammonia Borane

Inspired by the zwitterion species generated from the splitting of H₂ by frustrated Lewis pairs, we put forward a novel frustrated Lewis pair by the combination of H^δ‑ and H^δ+ incorporated Lewis acid and base together. Piers’ borane and chiral <i>tert</i>-butylsulfinamide were chosen as the FLP, and a metal-free asymmetric transfer hydrogenation of imines was realized with high enantioselectivities. Significantly, with ammonia borane as hydrogen source, a catalytic asymmetric reaction using 10 mol % of Piers’ borane, chiral <i>tert</i>-butylsulfinamide, and pyridine additive, has been successfully achieved to furnish optically active amines in 78–99% yields with 84–95% ee’s. Experimental and theoretical mechanistic studies reveal an interesting 8-membered ring hydrogen transfer transition state and an expected regeneration of reactive species with ammonia borane. Accordingly, a plausible catalytic pathway for this reaction is depicted

An Efficient Asymmetric Biomimetic Transamination of α‑Keto Esters to Chiral α‑Amino Esters

An efficient asymmetric biomimetic transamination of α-keto esters with quinine derivatives as chiral bases was described. A wide variety of α-amino esters containing various functional groups can be synthesized in high yield and enantioselectivity