Quantum Chemical Investigation of the Dimroth Rearrangement of 1‐(5‐Imino‐4,5‐dihydro‐1H‐1,2,3‐triazol‐1‐yl)anthracene‐9,10‐dione

This work is devoted to quantum chemical and experimental studies of the Dimroth rearrangement mechanism of 1‐(5‐imino‐4,5‐dihydro‐1H‐1,2,3‐triazol‐1‐yl)anthracene‐9,10‐dione. The study addresses how the bulky N‐ anthraquinonyl substituent affects the individual steps of the Dimroth rearrangement. The energy profile of the Dimroth rearrangement was calculated using density functional theory with the B3LYP approximation and the 6‐311++G(d,p) basis set. It was found that proton solvents (in particular, ethanol) play a critical role in hydrogen transfer via the hydrogen‐bond network, thereby ensuring the conversion of the initial triazene into a more stable cyclic 5‐aminotriazole. Further transformations involving ring opening and rotation do not have significant energy barriers. The final product is energetically most favorable, so the reaction proceeds easily in ethanol solution. The work demonstrates the convenience and efficiency of using the Dimroth rearrangement for the synthesis of new anthracenedione‐containing heterocycles. It provides an explanation of the mechanism of this rearrangement based on quantum‐chemical calculations for anthracene‐9,10‐dione derivatives.