N-{2-[(4S)-4-tert-Butyl-4,5-dihydro-1,3-oxazol-2-yl]phen-yl}-5,6-diphenyl-1,2,4-triazin-3-amine

Synthesis and structures of three new pyridine-containing oxazoline ligands of complexes for asymmetric catalysis

Three new chiral pyridine-containing oxazoline derivatives with fluorine and perfluoromethyl groups, namely, 2-({2-[(4S)-4-phenyl-4,5-dihydro-1,3-oxazol-2-yl]phenyl}amino)-5-(trifluoromethyl)pyridine, C₂₁H₁₆F₃N₃O, 2-({5-fluoro-2-[(4S)-4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl]phenyl}amino)-5-(trifluoromethyl)pyridine, C₁₈H₁₇F₄N₃O, and 2-({2-[(3aR,8aS)-8,8a-dihydro-3aH-indeno[1,2-d]oxazol-2-yl]phenyl}amino)-5-(trifluoromethyl)pyridine, C₂₂H₁₆F₃N₃O, as chiral ligands in metal-catalysed asymmetric reactions, were synthesized and characterized by spectral and X-ray diffraction methods. The conformation of the molecules is influenced by strong N-H...N hydrogen bonding and weak C-H...X (X = O and N) interactions. There are no intermolecular hydrogen bonds in the crystal structures of the analysed compounds. Hirshfeld surface analysis showed that the H...H contacts constitute a high percentage of the intermolecular interactions. The conformational analysis was performed by theoretical calculations using the density functional theory (DFT) method. The mechanism of complex formation in terms of the electron-withdrawing effect of the substituents on the oxazoline ring and the ligand conformation is discussed.

Chiral oxazoline ligands with two different six-membered azaheteroaromatic rings – synthesis and application in the Cu-catalyzed nitroaldol reaction

Synthesis and catalytic activity of chiral ligands 5,6-diphenyl-3-{3-[(4S/R)-4-R/Ar-4,5-dihydro-1,3-oxazol-2-yl]pyridin-2-yl}amino-1,2,4-triazines 2 and their analogs 3 possessing an N-oxide function in the pyridine ring are described. The pivotal step in the synthesis of ligands 2 is the Buchwald-Hartwig Pd-catalyzed cross-coupling reaction between 3-bromo-5,6-diphenyl-1,2,4-triazine (7a) and enantiopure 3-(4,5-dihydro-1,3-oxazol-2-yl)pyridin-2-amines 6a–d. Aromatic nucleophilic substitution of chlorine in 3-chloro-5,6-diphenyl-1,2,4-triazine (7b) with 3-(4,5-dihydro-1,3-oxazol-2-yl)pyridin-2-amine 1-oxides 12 was investigated as the key reaction in the synthesis of ligands 3. Two undesired derivatives 13 or 14, resulting from unexpected reactions of 3, were isolated depending on reaction conditions. Compounds 2 and 3 as well as the side products 13 and 14 were screened as chiral ligands in the copper catalyzed enatioselective nitroaldol reaction.

Structural characterization of copper complexes with chiral 1,2,4-triazine-oxazoline ligands

The crystal structure determination of oxazoline-1,2,4-triazine ligand