title: Gold- and platinum-catalyzed cycloisomerization of enynyl esters versus allenenyl esters: an experimental and theoretical study.
abstract: Ester-way to heaven: Unexpected formation of bicyclo[3.1.0]hexene 4 was the main focus of combined experimental and theoretical studies on the Au-catalyzed cycloisomerization of branched dienyne 1 (see scheme), which provided better understanding of the mechanistic details governing the cyclization of enynes bearing a propargylic ester group.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.
authors.affiliation: Institute of Chemical Research of Catalonia (ICIQ), Av. Països Catalans 16, 43007 Tarragona, Spain.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Marion
authors.forename: Gilles
authors.initials: G
authors.lastname: Lemière
authors.forename: Andrea
authors.initials: A
authors.lastname: Correa
authors.forename: Chiara
authors.initials: C
authors.lastname: Costabile
authors.forename: Rubén S
authors.initials: RS
authors.lastname: Ramón
authors.forename: Xavier
authors.initials: X
authors.lastname: Moreau
authors.forename: Pierre
authors.initials: P
authors.lastname: de Frémont
authors.forename: Rim
authors.initials: R
authors.lastname: Dahmane
authors.forename: Alexandra
authors.initials: A
authors.lastname: Hours
authors.forename: Denis
authors.initials: D
authors.lastname: Lesage
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Tabet
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Goddard
authors.forename: Vincent
authors.initials: V
authors.lastname: Gandon
authors.forename: Luigi
authors.initials: L
authors.lastname: Cavallo
authors.forename: Louis
authors.initials: L
authors.lastname: Fensterbank
authors.forename: Max
authors.initials: M
authors.lastname: Malacria
authors.forename: Steven P
authors.initials: SP
authors.lastname: Nolan