Enantioselective Ir I ‐Catalyzed Carbocyclization of 1,6‐Enynes by the Chiral Counterion Strategy

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.