Experimental Study on the Reaction Pathway of α-Haloacetophenones with NaOMe: Examination of Bifurcation Mechanism
作者:Kohei Tagawa、Keita Sasagawa、Ken Wakisaka、Shunsuke Monjiyama、Mika Katayama、Hiroshi Yamataka
DOI:10.1246/bcsj.20130253
日期:2014.1.15
The reaction of PhCOCH2Br and NaOMe in MeOH gave PhCOCH2OH as the major product and PhCOCH2OMe as the minor product. Substituent effects on the reactivity and product selectivity revealed that an electron-withdrawing substituent on the phenyl ring enhanced the overall reactivity and gave more alcohol than ether. It was indicated that the alcohol was formed via carbonyl addition-epoxidation, whereas the ether was formed by direct substitution. Substituent effects on the reaction rates, as well as the effects of NaOMe concentration on the rate and product ratio for both reactions of PhCOCH2Br and PhCOCH2Cl are in line with the mechanism that the alcohol and ether products were formed via two independent and concurrent routes, carbonyl addition and α-carbon attack, respectively, and thus the reaction mechanism could be different from the bifurcation mechanism previously predicted for the reaction of PhCOCH2Br by a simulation study in the gas phase.
在甲醇中,PhCOCH2Br与NaOMe的反应主要生成PhCOCH2OH,次要生成PhCOCH2OMe。取代基对反应活性和产物选择性的影响表明,苯环上的吸电子取代基增强了整体反应活性,生成更多的醇而非醚。表明醇是通过羰基加成-环氧化反应生成的,而醚是通过直接取代反应生成的。取代基对反应速率的影响,以及NaOMe浓度对PhCOCH2Br和PhCOCH2Cl反应速率和产物比例的影响,均与以下机理一致:即醇和醚产物分别通过两个独立且并行的路径——羰基加成和α-碳攻击生成,因此反应机理可能不同于之前气体相模拟研究中预测的PhCOCH2Br反应的分支机制。