Control of the 'extended' E1cB mechanism of acyl group transfer in activated esters of acrylic acids

Aminolysis and alkaline hydrolysis of aryl propenoates are shown to proceed via a normal nucleophilic substitution mechanism. The 'extended' E1cB mechanism of hydrolysis involving attack of hydroxide ion at the p carbon followed by expulsion of the phenolate ion from the resulting carbanion is shown not to occur with the parent propenoate. The ‘ extended ’ E1cB mechanism is taken by the hydrolysis of 2-cyano-3-(4-methoxyphenyl)propenoate esters due to the stabilising effect of the cyano-group on the intermediate carbanion.