Gold- And platinum-catalyzed cycloisomerization of enynyl esters versus alleneyl esters: An experimental and theoretical study

Nicolas Marion, Gilles Lemière, Andrea Correa, Chiara Costabile, Rubén S. Ramón, Xavier Moreau, Pierre De Frémont, Rim Dahmane, Alexandra Hours, Denis Lesage, Jean Claude Tabet, Jean Philippe Goddard, Vincent Gandon, Luigi Cavallo*, Louis Fensterbank, Max Malacria, Steven P. Nolan

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

116 Scopus citations

Abstract

Experimental and theoretical studies on Au- and Pt-catalyzed cycloisomerization of a branched dienyne with an acetate group at the propargylic position are presented. The peculiar architecture of the dienyne precursor, which has both a 1,6- and a 1,5-enyne skeleton, leads, in the presence of alkynophilic gold catalysts, to mixtures of bicyclic compounds 3, 4, and 5. Formation of unprecedented bicyclo[3.1.0]hexene 5 is the main focus of this study. The effect of the ancillary ligand on the gold center was examined and found to be crucial for formation of 5. Further mechanistic studies, involving cyclization of an enantioenriched dienyne precursor, 18 O-labeling experiments, and DFT calculations, allowed an unprecedented reaction pathway to be proposed. We show that bicyclo[3.1.0]hexene 5 is likely formed by a 1,3-OAc shift/allene-ene cyclization/ 1,2-OAc shift sequence, as calculated by DFT and supported by Au-catalyzed cyclization of isolated allenenyl acetate 7, which leads to improved selectivity in the formation of 5. Additionally, the possibility of OAc migration from allenyl acetates was supported by a trapping experiment with styrene that afforded the corresponding cyclopropane derivative. This unprecedented generation of a vinyl metal carbene from an allenyl ester supports a facile enynyl ester/allenenyl ester equilibrium. Further examination of the difference in reactivity between enynyl acetates and their corresponding [3,3]-rearranged allenenyl acetates toward Au- and Pt-catalyzed cycloisomerization is also presented.

Original languageEnglish (US)
Pages (from-to)3243-3260
Number of pages18
JournalChemistry - A European Journal
Volume15
Issue number13
DOIs
StatePublished - Mar 16 2009

Keywords

  • Alkynes
  • Allenes
  • Cycloisomerization
  • Density functional calculations
  • Gold

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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