The alkaline hydrolysis of the title esters, possessing three conjugated pi units between the internal nucleophile (the hydroxyl group) and the reaction center, follows an E1cB mechanism involving the participation of an "extra extended" p-oxo azoketene type intermediate. For the hydrolysis of the 2,4-dinitrophenyl ester kinetic data, activation parameters and trapping of the intermediate are consistent with a dissociative pathway carrying the reaction flux. The effect of the leaving group variation on reactivity agrees with the proposed mechanism, and the existence of an intermediate is also supported by diode array stopped-flow experiments. The presence of sp(2) nitrogen atoms in the conjugated backbone is beneficial to the dissociative mechanism.