The kinetics of cyclization of substituted phenyl N-(2-hydroxybenzyl)carbamates and their N-methyl analogs, prepared by the reaction of 2-(aminomethyl)phenols with substituted phenyl chloroformates, was studied in dioxane or toluene at the temperatures 110-180 °C. Electron-withdrawing substituents in the leaving phenoxy group strongly accelerate the rate of cyclization (ρ = 2.45 ± 0.15) while the substituents in the other ring have virtually no effect. The cyclization was catalyzed with triethylamine in toluene but not in dioxane. On the basis of these results, the most convenient method for preparation of substituted 4H-1,3-benzoxazin-2(3H)-ones was a one-hour reflux of substituted 4-nitrophenyl N-(2-hydroxybenzyl)carbamates in dioxane. Based on the influence of substituents, solvents (dioxane and toluene) and triethylamine, the reaction mechanism and structure of the transition state were proposed.
取代苯基N-(2-羟基苯甲基)氨基甲酸酯及其N-甲基类似物的环化动力学,通过2-(氨基甲基)酚与取代苯基氯甲酸酯反应制备,在二氧六环或甲苯中在110-180°C下进行研究。离去的苯氧基团中的电子吸引取代基强烈加速环化速率(ρ = 2.45 ± 0.15),而另一环中的取代基几乎没有影响。在甲苯中三乙胺催化了环化,但在二氧六环中没有。基于这些结果,制备取代4H-1,3-苯并噁唑-2(3H)-酮的最便捷方法是在二氧六环中将取代4-硝基苯基N-(2-羟基苯甲基)氨基甲酸酯回流一小时。根据取代基、溶剂(二氧六环和甲苯)和三乙胺的影响,提出了反应机理和过渡态的结构。