Mechanism of the Base-Catalyzed Elimination of Para-Substituted Phenoxides from 4-(Aryloxy)azetidin-2-ones

Article abstract of DOI:10.1021/jo00200a015

4-(Aryloxy)azetidin-2-ones 4-7 react in dilute aqueous alkali to give 3-hydroxyacrylamide oxyanion and para-substituted phenolate ions.Similarly, 4-(aryloxy)-3,3-dimethylazetidin-2-ones 8-11 give 2,2-dimethylcarboxaldoacetamide and para-substituted phenolate ions.Reactivity is proportional to the fraction of (aryloxy)azetidin-2-one anions, Ka/(Ka + ).Kinetic pKa's of 4-11 and first-order k₂'s for (suggested) reversible E1cB elimination of para-substituted phenoxide ions from N-1 anions are reported.Reactions are further characterized kinetically by solvent deuterium isotope effects: k_OH/k_OD = ca. 0.5, ρ(k₂) = 2.2 for 4-7 and ρ(k₂) = 2.7 for 8-11, and β_lg = -0.65 for 4-7 and β_lg = -0.75 for 8-11.