Lewis Acid-Promoted Three-Component Reactions of Propargylic Alcohols with 2-Butynedioates and Secondary Amines

We report herein a three-component reaction of propargylic alcohols with 2-butynedioates and secondary amines, which furnished functionalized dihydroazepines. In the cases where benzylmethylamine and benzyl-i-propylamine were used as the secondary amine, the reaction afforded 2,5-dihydro-1H-pyrroles and 2,3-dihydro-1H-pyrroles, respectively, as the major product along with the desired dihydroazepines. The reaction mode depends on the electronic and steric effect of the substitutents on the secondary amines used. A tentative mechanism for this cascade process is postulated. The key intermediate is ascribed to 1,3,4-pentatrien-1-amine, which is formed by trapping the in situ generating allenic carbocation with enamine. Because of the reactivity of 1,3,4-pentatrien-1-amine formed, different products were thus formed.本文报道了炔丙醇（propargylic alcohols）、丁炔二酸二酯（2-butynedioates）与仲胺（secondary amines）的三组分反应，该反应可生成官能化二氢氮杂卓（functionalized dihydroazepines）。当以苄基甲胺（benzylmethylamine）和苄基异丙基胺（benzyl-i-propylamine）作为仲胺时，反应分别主要生成2,5-二氢-1H-吡咯（2,5-dihydro-1H-pyrroles）与2,3-二氢-1H-吡咯（2,3-dihydro-1H-pyrroles），同时伴随目标产物二氢氮杂卓生成。该反应的模式取决于所用仲胺上取代基的电子效应与位阻效应。本文针对该级联过程提出了暂定机理：烯胺（enamine）捕获原位生成的联烯基碳正离子（allenic carbocation），得到关键中间体1,3,4-戊三烯-1-胺（1,3,4-pentatrien-1-amine）；基于该中间体的反应活性差异，最终生成了不同产物。