A New, “Elongated” Oxo Ketene Intermediate in the Dissociative Hydrolysis of 2,4-Dinitrophenyl (2E,4E)-5-(4‘-Hydroxyphenyl)pentadienoate

Abstract

Reactivity comparison, Arrhenius parameters, and trapping of the above-depicted unsaturated intermediate strongly suggest that the alkaline hydrolysis of the title ester follows a mechanism of the E1cB type. This is the first observation of the occurrence of a dissociative route in the hydrolysis of an acyl derivative with three π-systems interposed between the hydroxyl group (the internal nucleophile upon ionization) and the reaction center. Comparison with the hydrolysis of 2,4-dinitrophenyl 4‘-hydroxybenzoate shows that interposition of the vinylenic groups is beneficial to the dissociative route.