Abstract
A chiral phenol–NHC ligand enabled the copper-catalyzed enantioselective conjugate reduction of α,β-unsaturated esters. The phenol moiety of the chiral NHC ligand played a critical role in producing the enantiomerically enriched products. The catalyst worked well for various (Z)-isomer substrates. Opposite enantiomers were obtained from (Z)- and (E)-isomers, with a higher enantiomeric excess from the (Z)-isomer.
Highlights
Since the leading work of Stryker and co-workers on triphenylphosphine-stabilized copper hydride complexes [1,2], copper hydrides have been widely used for conjugate reductions of α,βunsaturated carbonyl compounds [3]
A chiral copper catalyst combined with a stoichiometric amount of a silane reagent, which generated copper hydride in situ, has successfully been utilized for enantioselective reactions with β,β-disubstituted α,β-unsaturated carbonyl compounds [4-11]
Chiral ligands based on N-heterocyclic carbenes (NHCs) [12] have not been applied to the conjugate reduction of α,β-unsaturated carbonyl compounds, while an achiral NHC/copper catalyst has successfully been utilized in this reaction [13]
Summary
Since the leading work of Stryker and co-workers on triphenylphosphine-stabilized copper hydride complexes [1,2], copper hydrides have been widely used for conjugate reductions of α,βunsaturated carbonyl compounds [3]. A chiral copper catalyst combined with a stoichiometric amount of a silane reagent, which generated copper hydride in situ, has successfully been utilized for enantioselective reactions with β,β-disubstituted α,β-unsaturated carbonyl compounds [4-11].
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