Paper
Selective mono-C-methylations of arylacetonitriles and arylacetates with dimethylcarbonate: a mechanistic investigation.
Published Jan 30, 2002 · P. Tundo, M. Selva, A. Perosa
The Journal of organic chemistry
40
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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 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 of the rate constants of model reactions involving 2-phenyl propionitrile, phenylacetonitrile, 2-methoxycarbonylphenylacetonitrile, and 2-methyl-2-methoxy carbonylphenyl acetonitrile (compounds 1a-4a, respectively) with DMC indicates that the methylation process is the fastest and the irreversible step, which drives the overall reaction to completion. The situation is reversed for arylacetic esters, where the methylation is more difficult than the demethoxycarbonylation reaction; therefore, a higher reaction temperature is required.
The high mono-C-methylation selectivity of arylacetic acid derivatives with dimethyl carbonate is due to a mechanism involving consecutive methoxycarbonylation, methylation, and demethoxycarbonylation steps, with methylation being the fastest and irreversible step.
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