N-esters (13) of 1H-pyrroles via competitive [1,5]sigmatropic rearrangements. Isolable intermediate 2H-pyrrole-2-carboxylic esters (l2) are converted similarly into the same products, under the same conditions. Detection of 3H-pyrroles (4) as intermediates in the latter reaction demonstrates for the first time the reversibility of the thermal 2H-pyrrole to 3H-pyrrole interconversion.
3H-吡咯-3-
羧酸酯(4)在某些情况下与具有外环双键的异构体(5)和(6)一起通过适当取代的2-乙氧基羰基-1,4-二酮(1)的环化反应制备用液
氨,然后在沸腾溶剂中用
铝矾土将可分离的2-羟基-
3,4-二氢-2H-吡咯中间体(2)和(3)脱
水。在
甲苯或
对二甲苯中长时间加热会通过竞争性的[1,5]σ重排将3H
吡咯(4)定量转化为1H-
吡咯的异构体4酯(11)和N-酯(13)。在相同条件下,将可分离的中间体2H-
吡咯-2-羧酸酯(l2)类似地转化为相同的产物。