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Enantioselective Ir I ‐Catalyzed Carbocyclization of 1,6‐Enynes by the Chiral Counterion Strategy
Author(s) -
Barbazanges Marion,
Augé Mylène,
Moussa Jamal,
Amouri Hani,
Aubert Corinne,
Desmarets Christophe,
Fensterbank Louis,
Gandon Vincent,
Malacria Max,
Ollivier Cyril
Publication year - 2011
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201102723
Subject(s) - chemistry , moiety , counterion , catalysis , enantioselective synthesis , cationic polymerization , medicinal chemistry , enantiomer , substrate (aquarium) , stereochemistry , ion , polymer chemistry , organic chemistry , oceanography , geology
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 (OP*) controls the enantioselectivity through formation of a loose ion pair with the metal center and establishes a CH⋅⋅⋅OP* 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 CC bond‐forming reaction.