Pyridinium (methoxycarbonyl)methylide generated from (methoxycarbonyl)methyl-pyridinium halides under the action of K2CO3 reacts with alkyl diazoacetates in CH2Cl2 at 20 °C, resulting in the successive addition of three CHCOOMe fragments from the ylide to form 3,6-bis(alkoxycarbonyl)-4,5-diazaoctadienoic acid diesters. Heating of the latter in the presence of pyridine leads to their isomerization to give tetraalkyl tetrahydropyridazine-tetracarboxylates in high yields. Under more drastic conditions (refluxing xylene in the presence of pyridine), the acyclic tetraesters undergo another transformation to form pyrrole-tetracarboxylic acid esters in yields of up to 60%.
在 K2CO3 的作用下,由(甲
氧基羰基)
甲基吡啶鎓卤化物生成的
吡啶鎓(甲
氧基羰基)甲化物与
重氮乙酸烷基
酯在
CH2Cl2 中于 20 °C 下发生反应,结果从醯胺中连续加入三个 CHCOOMe 片段,形成 3,6-双(烷
氧基羰基)-4,5-二
氮杂
辛二烯酸二
酯。在
吡啶存在下加热后者,会导致它们发生异构化,从而以高产率生成四烷基四
氢哒嗪四
羧酸盐。在更苛刻的条件下(在
吡啶存在下回流二
甲苯),无环四
酯会发生另一种转化,生成
吡咯-四
羧酸酯,产率高达 60%。