title: Enantioselective Ir(I)-catalyzed carbocyclization of 1,6-enynes by the chiral counterion strategy.
abstract: Enantioenriched bicyclo[4.1.0]hept-2-enes were synthesized by Ir(I)-catalyzed carbocyclization of 1,6-enynes. No chiral ligands were used, CO and PPh(3) were the only ligands bound to iridium. Instead, the stereochemical information was localized on the counterion of the catalyst, generated in situ by reaction of Vaska's complex (trans-[IrCl(CO)(PPh(3))(2)]) with a chiral silver phosphate. Enantiomeric excesses up to 93% were obtained when this catalytic mixture was used. (31)P NMR and IR spectroscopy suggest that formation of the trans- [Ir(CO)(PPh(3))(2)](+) moiety occurs by chlorine abstraction. Moreover, density functional theory calculations support a 6-endo-dig cyclization promoted by this cationic moiety. The chiral phosphate anion (O-P*) controls the enantioselectivity through formation of a loose ion pair with the metal center and establishes a C-H···O-P* hydrogen bond with the substrate. This is a rare example of asymmetric counterion-directed transition-metal catalysis and represents the first application of such a strategy to a C-C bond-forming reaction.
authors: UPMC Paris 06, IPCM (UMR CNRS 7201), 4 Place Jussieu, 75252 Paris cedex 05, France.
authors: Marion
authors: M
authors: Barbazanges
authors: Mylène
authors: M
authors: Augé
authors: Jamal
authors: J
authors: Moussa
authors: Hani
authors: H
authors: Amouri
authors: Corinne
authors: C
authors: Aubert
authors: Christophe
authors: C
authors: Desmarets
authors: Louis
authors: L
authors: Fensterbank
authors: Vincent
authors: V
authors: Gandon
authors: Max
authors: M
authors: Malacria
authors: Cyril
authors: C
authors: Ollivier