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. 2009 Mar 11;131(9):3160-1.
doi: 10.1021/ja809382c.

Efficient boron-copper additions to aryl-substituted alkenes promoted by NHC-based catalysts. enantioselective Cu-catalyzed hydroboration reactions

Yunmi Lee  1 , Amir H Hoveyda
Affiliations

Efficient boron-copper additions to aryl-substituted alkenes promoted by NHC-based catalysts. enantioselective Cu-catalyzed hydroboration reactions

Yunmi Lee et al. J Am Chem Soc. .

Abstract

A Cu-catalyzed method for efficient boron-copper addition processes involving acyclic and cyclic disubstituted aryl olefins are reported. Reactions are promoted with 0.5-5 mol % of a readily available N-heterocyclic carbene (NHC) complex; the presence of MeOH promotes in situ protonation of the C-Cu bond and leads to efficient catalyst turnover, constituting a net Cu-catalyzed hydroboration process. Reactions proceed in >98:<2 site selectivity and furnish secondary organoborane isomers that complement those obtained through reactions of boron-hydride reagents or by Rh- or Ir-catalyzed hydroborations (benzylic secondary C-B bonds). Initial observations regarding processes catalyzed by chiral NHC complexes, delivering products in up to 99:1 enantiomeric ratio, are disclosed.

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Figures

Scheme 1
Scheme 1
Cu–Catalyzed Hydroboration of Allylic Esters, Ethers and Alcohols
Scheme 2
Scheme 2
Cu–Catalyzed Enantioselective Hydroboration Reactionsa aSee SI for experimental details; oxidation conditions for 14–16: H2O2, 2.0 N aqueous NaOH; MeOH not used for 16. >98:<2 site-selectivity in all cases.
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