Different mechanisms have been proposed for the cyclization of enynes catalyzed by electrophilic metal halides or complexes. We present evidence to indicate that the previously reported “carbohydroxypalladation” and the “hydroxycyclization catalyzed by PtII” are closely related reactions. Thus, palladium complexes formed in situ from PdCl2 and trisulfonated phosphane TPPTS or cyclic phosphite P(OCH2)3CEt
Towards asymmetric Au-catalyzed hydroxy- and alkoxycyclization of 1,6-enynes
作者:Chung-Meng Chao、Emilie Genin、Patrick Y. Toullec、Jean-Pierre Genêt、Véronique Michelet
DOI:10.1016/j.jorganchem.2008.08.008
日期:2009.2
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.
Asymmetric Au-catalyzed domino cyclization/nucleophile addition reactions of enynes in the presence of water, methanol and electron-rich aromatic derivatives
作者:Alexandre Pradal、Chung-Meng Chao、Maxime R. Vitale、Patrick Y. Toullec、Véronique Michelet
DOI:10.1016/j.tet.2011.03.071
日期:2011.6
system is described for the asymmetric domino cyclization/functionalization reactions of functionalized 1,6-enynes in the presence of an external nucleophile. The use of (R)-4-MeO-3,5-(t-Bu)2-MeOBIHEP ligand associated with gold led to clean rearrangements implying the formal addition of an oxygen or carbon nucleophile to an alkene followed by a cyclization process. The enantiomeric excesses were highly