Abstract
The solvolytic behavior of 3-ethoxycarbonyl-2-phenyl-Δ2-pyrroline-4, 5-diones 7 depends on the N-substituents. On treatment with ethanol or methanol, the NH derivative 7a afforded the corresponding keto ester 9, a product of C5-lactam carbonyl attack, while the N-alkyl derivatives 7b-d gave the enols 8b-d, products of C2-attack. Kinetic analysis based on time dependent ultraviolet spectra of 7 in ethanolic solution revealed that the C2-center of the compound is the most electrophilic and that N-alkylation enhances the C2-electrophilicity. This increase in the electrophilicity can be rationalized in terms of the restricted rotation of the C2-phenyl group resulting from N-substitution, which prevents the phenyl-dioxopyrroline conjugation, thus destabilizing the dioxopyrroline form. In the solvolytic reaction of 7 in the presence of potassium hydroxide, the products were dependent on the solvent used. In methanol, 7a-b afforded the enolate 18a-b, while in water the carboxylate 19a-b was formed.
