Synlett 2004(13): 2429-2433  
DOI: 10.1055/s-2004-832824
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© Georg Thieme Verlag Stuttgart · New York

(R)-1,1′-Binaphthyl-2-bis(pentafluorophenyl)borane Lewis Acids

Darryl J. Morrison, Warren E. Piers*, Masood Parvez
Department of Chemistry, University of Calgary, 2500 University Drive N.W., Calgary, Alberta, T2N 1N4, Canada
Fax: +1(403)2899488; e-Mail: wpiers@ucalgary.ca;
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Publication History

Received 18 June 2004
Publication Date:
24 September 2004 (online)

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Abstract

A practical and high yielding synthetic route was developed for the preparation of optically pure (R)-(+)-2-bis(pentafluorophenyl)boryl-, (R)-(+)-1a,b, and (R)-2-difluoroboryl-1,1′-binaphthyls, (R)-5a,b. Chiral boranes (R)-1a and (R)-5a are active catalysts for the allylstannation of aromatic aldehydes although enantioselectivities for R products were low. A structural investigation of the adduct (±)-1a·o-anisaldehyde suggested that substituents in the 2′-position of the binaphthyl backbone could increase enantiofacial discrimination. Consistent with this structural study, the 2′-Me derivative (R)-1b gave slightly higher enantioselectivities and opposite configuration S of homoallylic alcohol products.