Elimination Reactions of Aryl Furylacetates Promoted by R₂NH-R₂NH₂⁺in 70 mol% MeCN(aq). Effects of β-Aryl on the Ketene-Forming Transition-State

Abstract

Ketene-forming elimination from 2-X-4-nitrophenyl furylacetates (1a-d) promoted by R 2 NH-R 2 NH 2 + in 70 mol % MeCN(aq) has been studied kinetically. When X = Cl and NO 2, the reactions exhibited second-order kinetics as well as Brönsted β = 0.37-0.54 and |β lg | = 0.31-0.45. The Brönsted β decreased with a poorer 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 OCH 3 (1b)], the reaction mechanism changed to the competing E2 and E1cb mechanisms. A further change to the E1cb mechanism was realized for the reaction of 1a with i-Pr 2 NH/i-Pr 2 NH 2 + in 70 mol % MeCN-30 mol % D 2 O. By comparing the kinetic results in this study with the existing data for ArCH 2 C(O)OC 6 H 3 -2-X-4-NO 2 , the effect of the β-aryl group on the ketene-forming elimination was assessed.

Elimination Reactions of Aryl Furylacetates Promoted by R2NH in MeCN: Effects of Base Solvent and β‐Aryl Group on the Ketene‐forming Transition State

“…The kinetic experiments were performed under pseudo‐first‐order condition . The kinetic plots showed straight lines with excellent correlations up to three half‐lives.…”

“…Aryl furylacetates 1a–1d were available in our laboratory . The products of the reaction of 1a–1d with R 2 NH in MeCN were characterized as before .…”

“…Aryl furylacetates 1a–1d were available in our laboratory . The products of the reaction of 1a–1d with R 2 NH in MeCN were characterized as before . The yields of aryloxides for the reactions of 1a–1d with R 2 NH in MeCN were determined as reported .…”

“…The proposal was invalidated by the experimental results demonstrating that the E2 mechanism changes to a competing E2 and E1cb and then to E1cb by the change in the reactant structure in the reactions of ArCH 2 C(O)OC 6 H 3 ‐2‐X‐4‐NO 2 (Ar = aryl, 3 ) with R 2 NH/R 2 NH 2 + in 70 mol% MeCN(aq) . Additional examples of such mechanistic changes were reported for eliminations from aryl thienylacetates (Ar = thienyl, 2 ) and aryl furylacetates (Ar = furyl, 1 ) under the same condition …”

“…(1)). By comparing with the existing data for elimination reactions from 1–3 promoted by R 2 NH/R 2 NH 2 + in 70 mol % MeCN(aq) and from 2 and 3 promoted by R 2 NH in MeCN, 4a,7,8 the effects of base solvent and β‐aryl groups are assessed.…”