Synthesis of 2-substituted pyrimidines and benzoxazoles via a visible-light-driven organocatalytic aerobic oxidation: enhancement of the reaction rate and selectivity by a base
作者:Lin Wang、Zhi-Gang Ma、Xiao-Jing Wei、Qing-Yuan Meng、Deng-Tao Yang、Shao-Fu Du、Zi-Fei Chen、Li-Zhu Wu、Qiang Liu
DOI:10.1039/c4gc00337c
日期:——
An efficient visible-light-driven photocatalytic oxidation of various 2-substituted dihydropyrimidines and phenolic imines has been achieved using an organic photocatalyst eosin Y bis(tetrabutyl ammonium salt) (TBA-eosin Y) and inexpensive oxidant molecular oxygen. With the aid of a base, significantly enhanced photoinduced electron transfer from substrates dihydropyrimidines or phenolic imines to the excited state of TBA-eosin Y has enabled the aerobic oxidation to yield 2-(methylthio)pyrimidines or 2-arylbenzoxazoles selectively.
A transition‐metal‐free approach to the alkylation/arylation of benzoxazole was developed by employing Tf2O‐activated‐amide as the alkylating/arylating reagent. The mild reaction conditions, and particularly insensitivity to air and water, further enhance the synthetic potential in pharmaceutical synthesis.
Efficient Cu-catalyzed intramolecular <i>O</i>-arylation for synthesis of benzoxazoles in water
作者:Yanling Tang、Minxin Li、Hui Gao、Gaoxiong Rao、Zewei Mao
DOI:10.1039/d0ra00570c
日期:——
An efficient method was developed for synthesis of benzoxazoles by Cu-catalyzed intramolecular O-arylation of o-halobenzanilides in water. This strategy provides several advantages, such as high yields, water as a green solvent and functional groups tolerance.
Palladium-catalyzed non-directed C–H bond arylation of difluorobenzenes and dichlorobenzenes bearing benzoxazole or benzothiazole
作者:Fatma Abdellaoui、Hamed Ben Ammar、Jean-François Soulé、Henri Doucet
DOI:10.1016/j.catcom.2015.07.025
日期:2015.11
We report, herein, on palladium-catalyzed direct arylation of difluorobenzenes and dichlorobenzenes bearing benzoxazole or benzothiazole moieties, which don't act as directinggroups. With moderate electron-withdrawing substituents on the aryl bromides as coupling partners, the reaction proceeds nicely using phosphine-free PdCl2 catalyst, and potassium pivalate/dimethylacetamide (PivOK/DMA) as catalytic
Through the confinement effect of the host-dye photocatalytic system to shift the redox potentials of substrate, the isomerization and thermodynamic activation of substrate were achieved, which were followed by a multiphotonexcitation enzymatic strategy for the generation of heterocycles by intramolecular C−X hydrogen evolution cross-couplings.