Abstract
| - 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 consecutivemethoxycarbonylation, methylation, and demethoxycarbonylation steps. Important aspects of thismechanism are clarified herein by a kinetic investigation. In the case of arylacetonitriles, at 140°C, the comparison of the rate constants of model reactions involving 2-phenyl propionitrile,phenylacetonitrile, 2-methoxycarbonylphenylacetonitrile, and 2-methyl-2-methoxy carbonylphenylacetonitrile (compounds 1a−4a, respectively) with DMC indicates that the methylation process isthe fastest and the irreversible step, which drives the overall reaction to completion. The situationis reversed for arylacetic esters, where the methylation is more difficult than the demethoxycarbonylation reaction; therefore, a higher reaction temperature is required.
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