1-Acyl-2-azabuta-1,3-dienes underwent rearrangement to 4-pyrrolin-2-ones in the presence of acidic catalysts (silica gel or ZnCl₂) and water. The reaction proceeded via the formation of 2,3-dihydroxy-3,4-dihydropyrrole and 2-hydroxy-2Н-pyrrole intermediates, the latter of which was transformed by [1,5]-sigmatropic shift of carbonyl substituent and prototropic isomerization. 4-Chloro-substituted 1-acetyl-2-azabuta-1,3-dienes were stable toward rearrangement, while brominated analogs rearranged into 4-pyrrolin-2-ones, probably as a result of the initial radical hydrodebromination. According to calculations performed at the DFT level, two steps of the reaction were catalyzed by acid: the cyclization of 2-azabutadiene and the sigmatropic shift in the 2-hydroxy-2Н-pyrrole intermediate.

中文翻译：

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酸催化的1-酰基-2-azabuta-1,3-二烯至4-吡咯啉-2-酮的重排

在酸性催化剂（硅胶或ZnCl ₂）和水的存在下，将1-酰基-2-azabuta-1，3-二烯进行重排，生成4-吡咯啉-2-酮。该反应通过形成2,3-二羟基-3,4-二氢吡咯和2-羟基-2Н-吡咯中间体而进行，中间体通过羰基取代基的[1,5]-σ位移和质子异构化而转化。4-氯取代的1-乙酰基-2-azabuta-1,3-二烯对重排稳定，而溴化类似物重排成4-吡咯啉-2-酮，这可能是由于最初的自由基加氢脱溴作用所致。根据在DFT级进行的计算，酸催化了反应的两个步骤：2-氮杂丁二烯的​​环化和2-羟基-2的σ位移Н-吡咯中间体。