Phosphorus in organic synthesis. IX. On the mechanism of esterification of malonic acid half esters by diphenyl phosphorazidate.
作者:KUNIHIRO NINOMIYA、TAKAYUKI SHIOIRI、SHUNICHI YAMADA
DOI:10.1248/cpb.22.1795
日期:——
The mechanism of esterification of malonic acid half esters by diphenyl phosphorazidate (DPPA) was investigated by treatment of some possible intermediates, such as mixed carboxylic phosphoric anhydrides and carboxylic acid azides, under similar reaction conditions to esterification, which revealed these are really intermediates of the esterification. Ethyl hydrogen (3, 4-methylenedioxybenzyl) methylmalonate (XI), which has no α-hydrogen to ester group, smoothly underwent the Crutius rearrangement instead of esterification under usual reaction conditions for the modified Curtius reaction by DPPA. This demonstrates that esterification takes place if substrates have an acidic hydrogen at the α-position to electron-withdrawing groups, allowing the formation of ketene intermediates. The overall mechanism is summarized in Chart 3.
通过处理一些可能的中间体,如混合羧酸磷酸酐和羧酸叠氮化物,在类似于酯化的反应条件下,研究了二苯基磷酸叠氮酸酯(DPPA)对马来酸半酯的酯化机制。这揭示了这些确实是酯化的中间体。乙基氢(3,4-亚甲基二氧苯基)甲基马来酸酯(XI)没有α-氢与酯基,在DPPA的改良Curtius反应的常规反应条件下顺利经历了Curtius重排,而不是酯化。这表明如果底物在与电子吸引基团相邻的α位有酸性氢,酯化反应会发生,从而使酮烯中间体的形成成为可能。整体机制总结在图3中。