Synthesis of 3-(Piperidin-4-yl)-6,7-dihydro-5h-pyrrolo-[2,1-c][1,2,4]triazole and Theoretical Study of the Hydrazone-Hydrazine Tautomerism of the Intermediate Hydrazonation Product

3-(Piperidin-4-yl)-6,7-dihydro-5H-pyrrolo[2,1-c][1,2,4]triazole was synthesized through a four-step process including etherification, hydrazonation, cyclization, and reduction with an overall yield of 39%. The final product was characterized by 1H NMR and ESI-MS/MS. The molecular structures of benzyl (Z)-4-(2-(pyrrolidin-2-ylidene)hydrazine-1-carbonyl)piperidine-1-carboxylate and related compounds were analyzed using DFT calculations at the B3LYP/6-311+G(d,p) level of theory. The results indicated a higher stability of the hydrazone tautomers.