Efficient Synthesis of Bulky 2,2’‐Bipyridine and (S)‐Pyridine‐Oxazoline Ligands

Abstract

Bulky N,N’‐bidentate ligands can furnish catalysts with enhanced catalytic activity compared to commercially available ligands. Straightforward methods to effectively synthesize a broad range of these ligands, however, are uncommon. In this work, a simple and efficient method is developed for the synthesis of bulky N,N’‐bidentate ligands, including 2,2’‐bipyridines and enantioenriched pyridine‐oxazolines. The Pd/NIXANTPHOS catalyst system enabled synthesis of a series of bulky 2,2’‐bipyridine‐based ligands and (S)‐pyridine oxazoline‐based enantioenriched ligands with good to excellent yields. The ligands have been benchmarked in the aminofluorination of styrene.

Chiral pyridine oxazoline and 1,2,4-triazine oxazoline ligands incorporating electron-withdrawing substituents and their application in the Cu-catalyzed enantioselective nitroaldol reaction

“…To investigate which of the above-mentioned factors has a decisive influence on the activity of ligands 1a-1c, 2a-2c, and 3a-3c, new pyridine oxazoline ligands 4a-4h, analogous to ligands 2a and 3a, whose structures were modified by introducing an electron-withdrawing group, were synthesized and examined in an enantioselective nitroaldol reaction. This studies are in line with still growing interest in pyridine-containing oxazoline ligands, the utility of which has recently been proved in many new asymmetric processes, e.g., aza-Wacker-type cyclization and C-H silylation [18][19][20][21][22][23]. Synthesis of new 1,2,4-triazine oxazoline ligands 5a-5d incorporating electron-withdrawing substituents was also performed and their activity in asymmetric nitroaldol reaction was investigated and compared to the activity of their counterparts 1a-1d without electronegative substituents.…”

Base-Catalyzed One-Pot Synthesis of 2,3,6-Substituted Pyridines

“…2-Substituted pyridine derivatives represent one of the most prevalent heterocycles found in pharmaceuticals, agrochemicals, organic ligands, and chemical sensors (Scheme ). − For instance, fluazinam A1 is a broad-spectrum and highly effective protective fungicide, and it has a good inhibition effect on phytophthora, uniaxial fungi, and sclerotinia. , Fluopicolide A2 is a broad-spectrum fungicide of pyrazolamide, which has excellent biological activity on common oomycete diseases. , 2-Pyridyl N -heteroarene A3 is a bidentate chelating ligand and could form complexes with many metal ions, which turn them into highly useful bidentate ligands in catalysis and organometallic chemistry. , Carbinoxamine A4 is a useful histamine H1 antagonist, and it is suitable for the treatment of allergic rhinitis and cold symptoms. , …”

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

“…In order to check the influence of the electron-withdrawing substituents on pyridine-containing oxazoline ligands, we designed and herein describe the synthesis, spectral characterization and crystal structure determination of three new pyridine-containing oxazoline ligands with fluorine and perfluoromethyl groups in the structures, namely, 2-({2-[(4S)-4-phenyl-4,5-dihydro-1,3oxazol-2-yl]phenyl}amino)-5-(trifluoromethyl)pyridine (5a), 2-({5-fluoro-2-[(4S)-4-isopropyl-4,5-dihydro-1,3-oxazol-2-yl]-phenyl}amino)-5-(trifluoromethyl)pyridine (5b) and 2-({2- [(3aR,8aS)-8,8a-dihydro-3aH-indeno[1,2-d]oxazol-2-yl]phenyl}amino)-5-(trifluoromethyl)pyridine (5c). Interest in pyridinecontaining oxazoline ligands is still growing (Zheng & Walsh, 2021;Li et al, 2020;Lai et al, 2020;Chen et al, 2019), even though they have been known since 1986 (Brunner et al, 1986). Moreover, these ligands have recently found application in many new asymmetric processes, e.g.…”