已经开发了一种介导的电合成方法用于甲基芳烃的选择性苄基氧化。N-羟基邻苯二甲酰亚胺的质子耦合电化学氧化产生的邻苯二甲酰亚胺-N-氧基(PINO)自由基作为氢原子转移(HAT)介体和原位产生的苄基自由基的自由基陷阱。相对于单电子转移(SET)引发的苄基氧化的直接电解方法,这种介导的电解方法在低得多的阳极电位下运行。将 SET 和介导的 HAT 电解方法与一组常见底物进行直接比较表明,HAT 反应表现出显着改善的底物范围和官能团兼容性。PINOylated产物在光化学条件下很容易转化为相应的苯甲醇或苯甲醛衍生物,并且非甾体抗炎药塞来昔布的后期功能化凸显了该方法的合成实用性。
Generation and cross-coupling of benzyl and phthalimide-N-oxyl radicals in a cerium(IV) ammonium nitrate/N-hydroxyphthalimide/ArCH2R system
作者:Alexander O. Terent'ev、Igor B. Krylov、Mikhail Y. Sharipov、Zoya M. Kazanskaya、Gennady I. Nikishin
DOI:10.1016/j.tet.2012.10.018
日期:2012.12
A method was developed for the cross-dehydrogenative coupling of alkylarenes and related compounds with N-hydroxyphthalimide (NHPI) using cerium(IV) ammonium nitrate (CAN) to prepare O-substituted NHPI derivatives. The characteristic feature of the reaction is that NHPI plays a dual role. Thus, in the presence of CAN, NHPI generates the phthalimide-N-oxyl (PINO) radical, which abstracts a hydrogen atom from the benzyl position to form a C-centered radical. The target oxidative cross-coupling product is formed mainly through the recombination of PINO with the C-centered radical. Therefore, NHPI serves as a mediator for the radical process and a reagent for the radical cross-coupling. The target products were obtained in yields from 35 to 80%. (c) 2012 Elsevier Ltd. All rights reserved.