A Frustrated Lewis Pair Catalyzed Asymmetric Transfer Hydrogenation of Imines Using Ammonia Borane.
Inspired by the zwitterion species generated from the splitting of H2by frustrated Lewis pairs, we put forward a novel frustrated Lewis pair by the combination of Hδ-and Hδ+incorporated Lewis acid and base together. Piers' borane and chiral tert-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 tert-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.
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
Songlei
S
Li
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
Gen
G
Li
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
Wei
W
Meng
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences , Beijing 100190, China.|University of Chinese Academy of Sciences , Beijing 100049, China.
Haifeng
H
Du