Mechanistic insights in gold-stabilized nonclassical carbocations: gold-catalyzed rearrangement of 3-cyclopropyl propargylic acetates - PubMed (original) (raw)

. 2010 Apr 7;132(13):4720-30.

doi: 10.1021/ja909013j.

Affiliations

Mechanistic insights in gold-stabilized nonclassical carbocations: gold-catalyzed rearrangement of 3-cyclopropyl propargylic acetates

David Garayalde et al. J Am Chem Soc. 2010.

Abstract

The reaction of 3-cyclopropyl propargylic carboxylates with Au(I) and Au(III) catalysts affords selectively 5-(E)-alkylidenecyclopentenyl acetates via [3,3]-sigmatropic rearrangement of the carboxylic moiety followed by cyclopropyl ring opening and cyclization. DFT calculations have been performed, supporting a two-step no-intermediate mechanism along the cyclization coordinate. The stereoselective formation of the exocyclic alkenes is kinetically controlled in the first of these events. Although stereospecific in nature through a gold-stabilized nonclassical carbocation, the chirality transfer in these cyclopentannulations is not complete. Computational and experimental evidence is provided for a Au-promoted cyclopropyl ring opening/epimerization/ring closure in both cis- and trans-cyclopropyl settings, which competes with the cyclization event, thus eroding the stereochemical information transfer. When tertiary acetates were used, products of both 1,2- and 1,3-acyloxy migration processes could be isolated, supporting the competitive coexistence of these two pathways along the reaction profile, as suggested also by DFT calculations.

PubMed Disclaimer

Publication types

MeSH terms

Substances

LinkOut - more resources