Selective Mono-<i>C</i>-methylations of Arylacetonitriles and Arylacetates with Dimethylcarbonate: A Mechanistic Investigation
作者:Pietro Tundo、Maurizio Selva、Alvise Perosa、Sofia Memoli
DOI:10.1021/jo0057699
日期:2002.2.1
The very high mono-C-methylation selectivity (>99%) of arylacetic acid derivatives (ArCH2X; X = CN, CO2Me) with dimethyl carbonate (DMC) is due to a mechanism that involves consecutive methoxycarbonylation, methylation, and demethoxycarbonylation steps. Important aspects of this mechanism are clarified herein by a kinetic investigation. In the case of arylacetonitriles, at 140 degrees C, the comparison
芳基丙烯酸衍生物(ArCH2X; X = CN,CO2Me)与碳酸二甲酯(DMC)的很高的单C-甲基化选择性(> 99%)是由于涉及连续的甲氧基羰基化,甲基化和脱甲氧基羰基化步骤的机理所致。该机理的重要方面在本文中通过动力学研究得以阐明。在芳基乙腈的情况下,在140摄氏度下比较涉及2-苯基丙腈,苯基乙腈,2-甲氧基羰基苯基乙腈和2-甲基-2-甲氧基羰基苯基乙腈的模型反应的速率常数(分别为化合物1a-4a) DMC分析表明,甲基化过程是最快且不可逆的步骤,可推动整个反应完成。芳基酯的情况则相反,甲基化比脱甲氧基羰基化反应困难的地方;因此,需要更高的反应温度。