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Efficient Pyrazole Moiety‐Containing Ligands for Cu‐Catalyzed O ‐Arylation of Phenols
Author(s) -
Zhao Yingying,
Wang Xiangyong,
Kaneyama Ryo,
Kodama Koichi,
Hirose Takuji
Publication year - 2020
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201903359
Subject(s) - chemistry , pyridine , moiety , catalysis , pyrazole , imine , medicinal chemistry , aryl , ligand (biochemistry) , halide , cumene , coupling reaction , density functional theory , phenols , photochemistry , stereochemistry , computational chemistry , organic chemistry , biochemistry , alkyl , receptor
Seven pyrazole‐ or pyridine‐containing N 2 ‐ and N 3 ‐ligalitnds ( L1 – L7 ) were developed for the ligand‐assisted CuI‐catalyzed coupling reactions of aryl halides with phenols. The structural and electronic effects were studied for various combinations of pyridine and/or imine nitrogen binding sites in the ligands. Screening their abilities showed most of them to be better than 4,4’‐dimethoxybipyridine ( L8 ). Among them, 2‐(1‐pyrazolyl)pyridine ( L1 ) featuring two types of binding sites gave the best results, with yields of up to 95% at 100 °C at a catalyst loading of 10 mol% (CuI/ L in 1 : 1 ratio). Free radical scavengers, 2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) (1.0 eq.) and cumene (1.0 eq.), lowered the yields by more than half, but the reaction was not completely quenched even when 3.0 eq. of TEMPO was used. A non‐radical and a radical mechanisms, are proposed for the L1 ‐promoted coupling reaction, well explained the experiments results. In addition, the structure of the catalyst species were elucidated through single crystal XRD and DFT (density functional theory) calculations.