SEMINARIO QUÍMICA ORGÁNICA 28-4-25
EXPOSITOR: Qco. Liddier Pérez Hincapié
TÍTULO: "Chiral N-Alkylfluorenyl-Substituted N-Heterocyclic Carbenes In The Gold(I)-Catalyzed Enantioselective Cycloisomerization Of 1,6-Enynes"
FUENTE: Robin Heinrich, Giovany Marie-Rose, Christophe Gourlaouen, Patrick Pale,Eric Brenner, and Aurélien Blanc, Chem. Eur. J. 2025, 31, e202404446
DÍA, HORA y LUGAR: Lunes 28 de abril de 2025, 14:00 h, Aula 18 y virtual.
Modalidad virtual, Link: meet.google.com/hjn-ygro-twf (Plataforma MEET GOOGLE)
Resumen:
A series of chiral A*Flu-NHC-gold(I) complexes, where A*Flu-NHC is an N-heterocyclic carbene (imidazolin-2-ylidene or benzimidazolin-2-ylidene) bearing a chiral 9-alkyl-9-fluorenyl N-substituent and a 2,6-diisopropylphenyl or benzyl N’-substituent, were straightforwardly prepared in few steps from readily available 2,6-diisopropylamine, imidazole or benzimidazole. The chirality of the N-substituent lies in the presence of a chiral alcoholic alkyl chain on the fluorenyl, which results from the opening of commercially available chiral styrene oxide, yielding to a 2-hydroxy-2-phenylethyl or a 2-hydroxy-1-phenylethyl group. Four [AuCl(A*Flu-NHC)] complexes were tested as precatalysts in an enantioselective cycloisomerization of a 1,6-enyne. Notably, the best inductions were observed with the benzimidazolin-2-ylidene derivative bearing a 2-hydroxy-1-phenylethyl group on the fluorenyl ring, showing that a constrained rotation around the N-Cfluorenyl bond and a chiral center in α position of the fluorenyl ring are determining factors. Interestingly, a strongimprovement of the induction with up to 72% ee was observed using AgOTf as activator. The presence of a hydrogen bond between the hydroxyl group and OTf- in the in situ generated active cationic gold(I) species probably stiffens its structure. This type of ligand-counteranion interaction represents a novel strategy for optimizing chirality transfer in asymmetric gold(I) catalysis.
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