Synthesis of new hybrid heterocycles based on transamination reactions of 3-[(dimethylamino)methylene]chromane-2,4-dione

Aminomethylidene derivatives of 4-oxochromen-2-one are polyfunctional synthons containing a conjugated enamine system, a lactone ring, and a carbonyl group in their structure. Due to the presence of multiple reaction centers, such compounds are widely used in directed organic synthesis to obtain a variety of condensed and hybrid heterocycles, many of which possess potential biological activity. The transamination reaction of enamines is a convenient and selective method for structural modification, allowing the replacement of the dimethylamino group with various heterocyclic moieties, in particular, with the 1,2,4-triazol-3-ylamino group. The transamination reaction of 3-((dimethylamino)methylene)chromane-2,4-dione and its thio analog was carried out by interaction with 1,2,4-triazol-3-amine in ethanol at room temperature. According to the mechanism of the process, the resulting product can exist in the E or Z form. Based on the results of quantum chemical calculations of the molecular geometry of the E and Z isomers, it is possible to make an assumption about the preferred isomer for each of the substances. It was found that the transamination reaction results in a change in conformation relative to the multiple bond of the product. This fact is supported by the upfield shift of the proton signal at the methylidene carbon atom due to a change in the spatial environment. Transamination under the action of 2-aminobenzimidazole proceeds via a stage of partial retro-cleavage of the enamine to the starting coumarin, followed by their condensation into a more complex condensed polycyclic system.