The cyclization reaction of substituted 2-(benzoylamino)alkanamides 1a-1i giving the corresponding substituted 2-phenylimidazol-4(5H)-ones 2a-2i has been studied. The equilibrium constants of reactions of compounds 1d-1f and 2-[(4-nitrobenzoyl)amino]-2,3-dimethylbutanenitrile (3) with methoxide have been determined in methanol-dimethyl sulfoxide media. For compound 1d and N-methyl derivatives 1a-1c, the cyclization rate constants have been measured in dependence on methoxide concentration in media of varying contents of dimethyl sulfoxide. The cyclization reaction mechanism involves formation of anion in a rapid pre-equilibrium and subsequent rate-limiting step: either formation of a cyclic intermediate or splitting off of OH- ion from this intermediate. The product formed in the given medium is immediately transformed into its conjugate base. A change in reaction medium affects the reactions of all the compounds in the same way. The ratio of concentration of substrate to that of its anion at low methoxide concentrations is affected by the solvent composition (MeOH-DMSO). At higher methoxide and DMSO concentrations the reaction rate distinctly decreases, which can be interpreted by the transformation of reactive anion into non-reactive dianion. The corresponding N-methylbenzoylamino compounds are cyclized faster by a factor of 400 as compared with compounds having no methyl group at the benzamide group.
研究了取代的2-(苯甲酰氨基)烷酰胺1a-1i的环化反应,得到相应的取代的2-苯基咪唑-4(5H)-酮2a-2i。在甲醇-二甲基亚砜介质中,确定了化合物1d-1f和2-[(4-硝基苯甲酰)氨基]-2,3-二甲基丁腈(3)与甲氧基的反应平衡常数。对于化合物1d和N-甲基衍生物1a-1c,测定了环化速率常数,取决于介质中甲氧基浓度的变化,介质中二甲基亚砜含量不同。环化反应机理涉及快速预平衡中阴离子的形成和随后的速率限制步骤:要么形成环中间体,要么从该中间体中分离出OH-离子。在给定介质中形成的产物立即转化为其共轭碱。反应介质的改变以相同的方式影响所有化合物的反应。在低甲氧基浓度下,底物浓度与其阴离子的比值受溶剂组成(MeOH-DMSO)的影响。在较高的甲氧基和DMSO浓度下,反应速率明显降低,这可以解释为反应性阴离子转化为非反应性二阴离子。与苯酰胺基上没有甲基的化合物相比,相应的N-甲基苯甲酰氨基化合物的环化速度快400倍。