A Quantum Chemical Study on the Mechanisms of Acylpyrrolylacetylenes Reactions With 1‐Pyrrolines

The mechanisms of reactions between electron‐deficient acetylenes, specifically acylpyrrolylacetylenes, and 1‐pyrrolines were examined using a DFT B2PLYP‐D3/6‐311++G**//B3LYP/6‐31+G* approach. The study was focused on the interaction of 1‐phenyl‐3‐(1H‐pyrrol‐2‐yl) prop‐2‐yn‐1‐one with 5‐methyl‐3,4‐dihydro‐2H‐pyrrole, and was aimed at a clearer understanding of the reaction progress. The reaction pathway for the synthesis of a dipyrroloimidazole derivative comprising three five‐membered nitrogen‐containing heterocycles is compared to one typical for N‐substituted acylethynylpyrroles, which involves opening the pyrroline ring to form δ‐keto aminoenones. An explanation is presented for the high level of deuterium exchange during the reaction in deuterated methanol. Also, the impact of trace water in acetonitrile was assessed. A ring‐opening mechanism is proposed, involving the 1‐pyrroline molecule as a base. The photochemical isomerization process of the end product is also examined.