Efficient Selenium-Catalyzed Selective C(sp<sup>3</sup>)−H Oxidation of Benzylpyridines with Molecular Oxygen
作者:Weiwei Jin、Poonnapa Zheng、Wing-Tak Wong、Ga-Lai Law
DOI:10.1002/adsc.201601065
日期:2017.5.2
An efficient selenium‐catalyzed direct oxidation of benzylpyridines in aqueous DMSO has been successfully developed by using molecularoxygen as the oxidant. A variety of benzoylpyridines with broad functional group tolerance were obtained in modest to excellent yields and with exclusive chemoselectivity.
The oxidation of benzylpyridines forming benzoylpyridines was achieved based on a synergistic H4NI-AcOH catalyst and molecular oxygen in high yield under solvent-free conditions. This is the first nonmetallic catalytic system for this oxidation transformation using molecular oxygen as the oxidant. The catalytic system has a wide scope of substrates and excellent chemoselectivity, and this procedure can also be scaled up. The study of a preliminary reaction mechanism demonstrated that the oxidation of the C-sp(3)-H bonds of benzylpyridines was promoted by the pyridinium salts formed by AcOH and benzylpyridines. The synergistic effect of H4NI-AcOH was also demonstrated by control experiments.
Cobalt(II)-based Metalloradical Activation of 2-(Diazomethyl)pyridines for Radical Transannulation and Cyclopropanation
A new catalytic method for the denitrogenative transannulation/cyclopropanation of in‐situ‐generated 2‐(diazomethyl)pyridines is described using a cobalt‐catalyzed radical‐activation mechanism. The method takes advantage of the inherent properties of a CoIII‐carbene radical intermediate and is the first report of denitrogenative transannulation/cyclopropanation by a radical‐activation mechanism, which
Metal‐Free Halogen(I) Catalysts for the Oxidation of Aryl(heteroaryl)methanes to Ketones or Esters: Selectivity Control by Halogen Bonding
作者:Somraj Guha、Govindasamy Sekar
DOI:10.1002/chem.201801717
日期:2018.9.20
for this crucial step. Isotope‐labeling and other supporting experiments suggested that a Kornblum‐type oxidation with DMSO and aerobic oxygenation with molecular oxygen took place simultaneously. A background XB‐assisted electron transfer between the heteroarenes and halogen(I) catalysts was responsible for the formation of heterobenzylic radicals and, thus, the aerobic oxygenation. For selective acyloxylation