Elimination Reactions of Aryl Furylacetates Promoted by R2NH-R2NH_2~+ in 70 mol % MeCN(aq). Effects of β-Aryl on the Ketene-Forming Transition-State

摘要

Ketene-forming elimination from 2-X-4-nitrophenyl furylacetates (1a-d) promoted by R2NH-R2NH_2+~ in 70 mol % MeCN(aq) has been studied kinetically. When X = Cl and NO2, the reactions exhibited second-Order kinetics as well as Bronsted β = 0.37-0.54 and |β_(lg)| = 0.31-0.45. The Bronsted (3 decreased with apoorer leaving group and |β_(lg)| increased with a weaker base. The results are consistent with an E2 mechanism When the leaving group was changed to a poorer one [X= H (1a) and OCH3 (1b)], the reaction mechanism changed to the competing E2 and Elcb mechanisms. A further change to the Elcb mechanism was realized for the reaction of 1a with i-Pr2NH/i-Pr2NH_2+~in 70 mol % MeCN-30 mol % D2O. By comparing the kinetic results in this study with the existing data for ArCH2C(O)OC6H3-2-X-4-NO2, the effect of the β-aryl group on the ketene-forming elimination was assessed.