898779-90-3Relevant academic research and scientific papers
Metal-Free Halogen(I) Catalysts for the Oxidation of Aryl(heteroaryl)methanes to Ketones or Esters: Selectivity Control by Halogen Bonding
Guha, Somraj,Sekar, Govindasamy
, p. 14171 - 14182 (2018/09/10)
Metal-free halogen(I) catalysts were used for the selective oxidation of aryl(heteroaryl)methanes [C(sp3)?H] to ketones [C(sp2)=O] or esters [C(sp3)?O]. The synthesis of ketones was performed with a catalytic amount of NBS in DMSO solvent. Experimental studies and density functional theory (DFT) calculations supported the formation of halogen bonding (XB) between the heteroarene and N-bromosuccinimide, which enabled imine–enamine tautomerism of the substrates. No additional activator was required 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 (ester formation), a catalytic amount of iodine was employed with tert-butyl hydroperoxide in aliphatic carboxylic acid solvent. Several control reactions, spectroscopic studies, and Time-Dependent Density Functional Theory (TD–DFT) calculations established the presence of acetyl hypoiodite as an active halogen(I) species in the acetoxylation process. With the help of a selectivity study, for the first time we report that the strength of the XB interaction and the frontier orbital mixing between the substrates and acyl hypoiodites determined the extent of the background electron-transfer process and, thus, the selectivity of the reaction.
Cobalt(II)-based Metalloradical Activation of 2-(Diazomethyl)pyridines for Radical Transannulation and Cyclopropanation
Roy, Satyajit,Das, Sandip Kumar,Chattopadhyay, Buddhadeb
, p. 2238 - 2243 (2018/02/19)
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 is supported by various control experiments. The synthetic benefits of the metalloradical approach are showcased with a short total synthesis of (±)-monomorine.
Efficient Selenium-Catalyzed Selective C(sp3)?H Oxidation of Benzylpyridines with Molecular Oxygen
Jin, Weiwei,Zheng, Poonnapa,Wong, Wing-Tak,Law, Ga-Lai
supporting information, p. 1588 - 1593 (2017/05/05)
An efficient selenium-catalyzed direct oxidation of benzylpyridines in aqueous DMSO has been successfully developed by using molecular oxygen as the oxidant. A variety of benzoylpyridines with broad functional group tolerance were obtained in modest to excellent yields and with exclusive chemoselectivity. (Figure presented.).
Synergistic H4NI-AcOH Catalyzed Oxidation of the Csp3-H Bonds of Benzylpyridines with Molecular Oxygen
Ren, Lanhui,Wang, Lianyue,Lv, Ying,Li, Guosong,Gao, Shuang
supporting information, p. 2078 - 2081 (2015/05/13)
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 Csp3-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. (Figure Presented).
