Ultrasound-Assisted Utility of 1,2,4-Triazole as a Multisite-Sequential Scaffold to Construct Different Heterocycles, Accredited by Molecular Modeling and Electrochemical Studies

In the present work, the tail approach chemical reactivity of 4-amino-5-hydrazinyl-4H-1,2,4-triazole-3-thiol (1) with trade name purpald towards various carbonyl groups is exploited to synthesize heterocyclic molecules such as triazine, tetrazine, and thiadiazepine fused and integrated with the triazole scaffold. The controlled and effective reaction of the site-selective hydrazinyl group proceeds smoothly in acidified methanol at ambient conditions under ultrasonic irradiation as an eco-friendly method enhancing product purity with easier work-up in a shorter reaction time compared with conventional methods. It was observed that the final products were obtained in high yields (89%–99%) in 0.25–5 min by the sonochemical method versus 68%–94% by the conventional method in a time range of 2–35 min. Further to this, the economic yields (YE) of the synthesized compounds were calculated to confirm and compare the efficiency of the two different synthetic methods. Moreover, computational studies were conducted to clarify the regiodivergence of tautomeric forms of 1,2,4-triazol-3-yl-hydrazineylidene-6-hydroxypyrimidine-2,4(3H,5H)-dione 26 and elucidate the most optimized tautomer via using density functional theory (DFT). Furthermore, most of the synthesized heterocyclic systems 26, 5, 29, 6, 22, and 24 in the same order, which were fabricated by the ultrasonication technique, showed excellent conductivity and low resistivity than other investigated scaffolds 3, 8, 11, 12, 14, 16, 17, 19, and 21, depending on electrochemical impedance spectroscopy measurements.