Reactions of carbonyl compounds in basic solutions. Part 25.1 The mechanism of the base-catalysed ring fission of 3,4-diphenylcyclobut-3-ene-1,2-diones
作者:Abdulaziz Al-Najjar、Keith Bowden、M. Vahid Horri
DOI:10.1039/a606412d
日期:——
The rate coefficients for the base-catalysed ring fission of a
series
of substituted 3,4-diphenylcyclobut-3-ene-1,2-diones to give the
corresponding (Z)-2-oxo-3,4-diphenylbut-3-enoic acids
have been determined in 50% (v/v) aqueous dimethyl sulfoxide (DMSO) at
25.0 and 45.0 °C, as well as for a limited series in
70% (v/v) aqueous DMSO. The activation parameters have been calculated.
The effect of both mono- and di-substitution of the phenyl groups has
been studied and gives a Hammett ρ value of
ca. 1.3 in 50% aqueous DMSO at
25.0 °C. The kinetic solvent isotope and solvent
effect and enrichment in 18O-enriched water have been
studied. The product composition of the reaction of the monosubstituted
compounds gave a ρ value of ca. 0.9.
All the evidence indicates a mechanistic pathway which proceeds by a
rapid, reversible addition of hydroxide anion to the dione, followed by
a benzilic acid-type rearrangement to form a
1-hydroxycyclopropene-1-carboxylic acid. The latter then suffers ring
fission to give the final product.
在50%(v/v)水溶性二甲基亚硫酰胺(DMSO)中,基催化的环裂解反应速率系数已被确定,涉及一系列取代的3,4-二苯基环丁烯-1,2-二酮,生成相应的(Z)-2-氧基-3,4-二苯基丁-3-烯酸,实验温度为25.0和45.0°C,同时在70%(v/v)水溶性DMSO中对有限系列也进行了测定。激活参数已被计算出。对苯基团的单取代和双取代效果进行了研究,得到了在25.0°C的50%水溶性DMSO中Hammett ρ值约为1.3。还研究了动力学溶剂同位素效应及在富集18O的水中的溶剂效应。单取代化合物反应的产物组成给出了约0.9的ρ值。所有证据表明,反应机制是通过羟基阴离子快速、可逆地添加到二酮,随后发生类苯基酸重排,形成1-羟基环丙烯-1-羧酸。后者再经历环裂解,生成最终产物。