DDQ / H +系统易于将各种电子供体氧化,氧化电位高达1.7 V,可氧化成相应的阳离子自由基。使用DDQ / H +和常用的FeCl 3作为氧化剂对Scholl反应中有争议的氢离子与阳离子自由基机理的重新检验,使我们证明反应主要是通过阳离子自由基机理进行的。支持Scholl反应的阳离子自由基途径的重要实验证据包括:(i)在二氯甲烷和各种酸(10%v / v)的混合物中,Scholl前体中没有反应。(ii)必须使用强氧化剂,例如氯化铁(FeCl 3)或DDQ / H +考虑到二氢中间体的芳构化(通过芳烃离子机理形成)可以很容易地用相当弱的氧化剂(例如碘或空气)来完成,因此Scholl反应与芳烃离子机理不一致。(iii)与SCE相比,氧化电位≤1.7V的各种Scholl前体易于形成DDQ / H +作为氧化剂的C-C氧化键,而与SCE相比,氧化电位大于1.7 V的Scholl前体则不会发生
Oxidative C−C Bond Formation (Scholl Reaction) with DDQ as an Efficient and Easily Recyclable Oxidant
作者:Linyi Zhai、Ruchi Shukla、Rajendra Rathore
DOI:10.1021/ol901331p
日期:2009.8.6
DDQ in the presence of an acid is known to oxidize a variety of aromatic donors to the corresponding cation radicals. Herein, we now demonstrate that the DDQ/H+ system can be effectively utilized for the oxidative C-C bond formations or biaryl synthesis. The efficient preparation of a variety of polyaromatic hydrocarbons including graphitic hexa-peri-hexabenzocoronenes, ease of isolation of the clean products, and ready regeneration of DDQ from easily recovered reduced DDQ-H-2 advances the use of DDQ/H+ for Scholl reactions.