Divergent Synthesis of 1<i>H</i>-Indazoles and 1<i>H</i>-Pyrazoles from Hydrazones<i>via</i>Iodine-Mediated Intramolecular Aryl and<i>sp</i><sup>3</sup>C-H Amination
by condensation of hydrazines with the corresponding ketones. In the presence of potassium iodide, I2-mediated oxidative cyclization of diaryl and tert-butyl aryl ketone hydrazones produced 1H-indazoles via direct aryl C–H amination. Under similar reaction conditions, primary and secondary alkyl ketone hydrazones were transformed into 1H-pyrazole products in a reaction involving sp3 C–H amination. This
A transition‐metal‐free oxidativeCN coupling method has been developed for the synthesis of 1H‐azaindazoles and 1H‐indazoles from easily accessible hydrazones. The procedure uses TEMPO, a basic additive, and dioxygen gas as the terminal oxidant. This reaction demonstrates better reactivity, functional group tolerance, and broader scope than comparable metal catalyzed reactions.
[Bis-(trifluoroacetoxy)iodo]benzene-Mediated Oxidative Direct Amination C-N Bond Formation: Synthesis of 1<i>H</i>-Indazoles
作者:Zhiguo Zhang、Yuanyuan Huang、Guoqing Huang、Guisheng Zhang、Qingfeng Liu
DOI:10.1002/jhet.2839
日期:2017.7
An efficient [bis‐(trifluoroacetoxy)iodo]benzene (PIFA)‐mediated oxidative C‐N bond formation is developed for the synthesis of 1H‐indazoles from readily available arylhydrazones. The reaction tolerates a wide range of functional groups and has broad scope of substrates. Moreover, this method is a relative green and reliable method for rapid preparation of substituted 1H‐indazoles under mild conditions
A simple, practical, and highly efficient synthesis of pyrazoles and indazoles via copper-catalyzed direct aerobic oxidative C(sp2)–H amination has been reported herein. This process tolerated a variety of functional groups under mild conditions. Further diversification of pyrazoles was also investigated, which provided its potential for drug discovery.
1H-indazole and derivatives was accomplished on the basis of the iodobenzene-catalyzed intramolecular C–Hamination of hydrazones undermildconditions. Reactions of hydrazones derived from ketones and hydrazines with a catalytic amount of iodobenzene in the presence of Oxone as an oxidant in trifluoroacetic acid took place to afford 1H-indazoles in moderate to good yields. A plausible reaction mechanism