Enantioselective Alkynylation of 2-Trifluoroacetyl Imidazoles Catalyzed by Bis-Cyclometalated Rhodium(III) Complexes Containing Pinene-Derived Ligands.
Chiral rhodium(III) complexes containing two cyclometalating 2-phenyl-5,6-(S,S)-pinenopyridine ligands and two additional acetonitriles are introduced as excellent catalysts for the highly enantioselective alkynylation of 2-trifluoroacetyl imidazoles. Whereas the ligand-based chirality permits the straightforward synthesis of the complexes in a diastereomerically and enantiomerically pure fashion, the metal-centered chirality is responsible for the asymmetric induction over the course of the catalysis. For comparison, the analogous iridium congeners provide only low enantioselectivity, and previously reported benzoxazole- and benzothiazole-based catalysts do not show any catalytic activity for this reaction under standard reaction conditions.
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany.
Yu
Y
Zheng
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany.
Klaus
K
Harms
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany. zhangl@staff.uni-marburg.de.
Lilu
L
Zhang
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043, Marburg, Germany. meggers@chemie.uni-marburg.de.|College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, 361005, P. R. China. meggers@chemie.uni-marburg.de.
Eric
E
Meggers
alkynylation; asymmetric catalysis; chirality; cyclometalation; rhodium; trifluoromethyl