Towards asymmetric Au-catalyzed hydroxy- and alkoxycyclization of 1,6-enynes

The efficiency of a Au(III)/chiral ligand system has been studied. The association of several chiral mono- and bidentate phosphanes with gold has been tested in the formal addition of an oxygen nucleophile to an alkene followed by a cyclization process, namely the hydroxycyclization reaction of 1,6-enynes. The use of ( R)-4-MeO-3,5-(t-Bu)(2)-MeOBIPHEP ligand led to clean cycloisomerizations and afforded the highest enantiomeric excesses. The enantiomeric excesses were highly dependant on the substrate/nucleophile combination. A P-31 NMR study of the catalytic species tends to prove that Au( III) catalyst may be reduced to Au( I) intermediate in the presence of phosphanes. (C) 2008 Elsevier B.V. All rights reserved.