自由基促进的醇/醚α-O-C(sp^3)—H键选择性活化的最新研究进展

Recent Advances in Free-Radical-Promoted Selective Activation of Alcohol/Ether α-O-C(sp^3)-H Bond

醇/醚是最常见的化工原料,而醇羟基被认为是合成化学中的"万能"官能团转化基团.选择性地切断醇/醚分子中α-氧原子位的C(sp^3)—H键,构筑新的化学键,无疑是一种十分有吸引力的合成策略.近年来,一些很高效的经自由基历程的这类转化被相继报道.醇/醚作为起始原料,羟基的有效保留以及专一的区域选择性等优点使得此类合成方法备受关注.概述了近年来经自由基促进的脂肪醇及醚α-氧C(sp^3)—H键选择性活化构建C—C键的最新研究进展.

Alcohols/ethers are the most common chemicals. And the hydroxyl group in alcohols is believed to be universal functional group in synthetic organic chemistry. It is undeniably attractive to form a new chemical bond through selective cleavage of the α-O-C（sp^3）—H bond. Considerable developments in the free-radical-promoted alcohol/ether C（sp^3）—H functionalization have been achieved in recent years. These methods have drawn much attention from synthetic chemists due to the features of alcohol/ether as starting materials, reservation of the hydroxyl group and excellent regioselectivity, etc. This paper summarizes the recent advances in free-radical-initiated selective activation of the α-O-C（sp^3）—H bonds in alcohol/ether. For a start, the possible factors such as bond dissociation energy（BDE） and stability of the key radical intermediate that dominates the regioselectivity in radical-initiated C（sp^3）—H bond activation have been analyzed here. Moreover, recent developments in this field have been demonstrated in details from different reaction types as following.（a） Minisci reactions of heterocycles with alcohols/ethers;（b） Radical addition/elimination reactions of activated alkenes with alcohols/ethers;（c） Free-radical addition/cyclization cascade reactions of activated olefins and/or biaryl isonitriles with alcohols/ethers;（d） Free-radical addition/difunctionalization and rearrangement reactions of alcohols/ethers with activated alkenes. Besides, other free radical reactions such as oxidative coupling reactions of aryl boronic acids with ethers, C—O and C—N bond formation reactions have also been exhibited. In addition, the suggested mechanisms for most of these reactions have been depicted and discussed in this review. Finally, the disadvantages of present systems and the possible modifications along with the future studies of this active area have been summarized at the end of this article.