Copper Hydride Catalyzed Enantioselective Conjugate Reduction of Unsaturated Nitriles

Abstract

α,β-Unsaturated nitriles were reduced with high levels of enantioselectivity via copper hydride catalysis. In this procedure, bench-top stable copper(II) acetate and Josiphos ligand are used as the chiral catalyst and an inexpensive hydrosilane, polymethylhydrosiloxane (PMHS) is employed as the stoichiometric reducing agent. While the reactions are conducted at 0 °C in most cases, they also can be conducted at room temperature at enhanced rates with no significant drop in enantiomeric excess.

asymmetric catalysis - copper hydride - hydrosilanes - reduction - α,β-unsaturated nitriles

References

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<A NAME="RZ03707SS-5">5</A> (R)-(S)-Josiphos (R)-(S)-PPF-PCy₂ = dicyclohexyl{(R)-1-[(S)-2-(diphenylphosphino)ferrocenyl]ethyl}phosphine. For a review, see: Blaser H.-U. Brieden W. Pugin B. Spindler F. Studer M. Togni A. Top. Catal.  2002,  19:  3 

<A NAME="RZ03707SS-6">6</A>

BINAP = 2,2′-bis(diphenylphosphino)-1,1′-binaphthalene.

<A NAME="RZ03707SS-7">7</A>

p-Tol-BINAP = 2,2′-bis(di-4-tolylphosphino)-1,1′-bi­-naphthalene.

<A NAME="RZ03707SS-8">8</A>

(R)-(S)-PPF-Pt-Bu₂ = di-tert-butyl{(R)-1-[(S)-2-(diphenyl-phosphino)ferrocenyl]ethyl}phosphine.

<A NAME="RZ03707SS-9">9</A>

(R)-(S)-Cy₂PF-PCy₂ = dicyclohexyl{(R)-1-[(S)-2-(dicyclo-hexylphosphino)ferrocenyl]ethyl}phosphine.

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