Radical-mediated activation of C-H bonds

Abstract

Functionalization of C-H bonds is synthetically important and has attracted a great deal of recent attention among organic chemists. Activation of C-H bonds using a chlorine atom as a radical mediator was investigated. The chlorine atom was generated by thermal or photochemical decomposition of ally] 2-chloroethylsulfone and cleaved C-H bonds to give alkyl radicals. Radical-mediated acylation, vinylation, cyanation and allylation of C-H bonds were studied. Under photochemically initiated conditions, reactions of phenylsulfonyl oxime ether with either cyclic ether or acyclic ether resulted in the formation of a-oxime ether substituted ethers in good yields. With unactivated hydrocarbons such as cyclohexane and adamantane, the present approach was unsuccessful. Several vinyl sulfones were examined for vinylation of C-H bonds. Among them, symmetric vinyl sulfone, l ,2-bis(phenylsulfonyl)ethylene, gave the best results. In cyanation reaction, using the p-toluenesulfonyl cyanide, the desired cyanation products were obtained from 18-crown-6 and dibenzyl ether. With unactivated hydrocarbons as the substrates, the satisfactory yields were not obtained. Allyl sulfones underwent similar free radical reactions, resulting in allylation of substrate. Due to polar effects, the reactions benefit from the presence of electron-withdrawing group at the 2-position of the allylsulfones.