N-Heterocyclic Carbene-Cu-Catalyzed Enantioselective Allenyl Conjugate Addition
Qinglei Chong1, Shuoqing Zhang2, Fengchang Cheng1
1State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis , Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences , 345 Lingling Road , Shanghai 200032 , China.
Abstract:
A catalytic enantioselective conjugate addition with commercially available allenylboronic acid pinacol ester as nucleophile promoted by a chiral copper complex of N-heterocyclic carbene (NHC) is disclosed. This process constitutes an unprecedented instance of the conjugate addition that introduces an allenyl group into α,β-unsaturated carbonyl compounds, affording products that are otherwise difficult to access in up to 92% yield, >98% allenyl addition selectivity and 96:4 enantiomeric ratio. DFT calculations were performed to elucidate the origins of enantioselectivity.
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