Efficient Synthesis and X-ray Structure of [1,2,4]Triazolo[4,3-a]pyridines via Oxidative Cyclization Using N-Chlorosuccinimide (NCS)

Triazolopyridines are a family of compounds that, owing to their biological activity, have many pharmaceutical applications. In this study, 3-(pyridine-4-yl)-[1,2,4]triazolo[4,3-a]pyridine and 6-bromo-3-(pyridine-4-yl)-[1,2,4]triazolo[4,3-a]pyridine were synthesized by using the chlorinated agent NCS for hydrazones under very mild conditions. The characterization of these compounds was achieved by 1H NMR, 13C NMR, FTIR, MS and X-ray diffraction. The compound 3-(pyridine-4-yl)-[1,2,4]triazolo[4,3-a]pyridine was crystallized in the monoclinic space group P 21/c with a = 15.1413(12), b = 6.9179(4), c = 13.0938(8) Å, β = 105.102(6)°, V = 1324.16(16)Å3, Z = 4, and R = 0.0337. Also compound 6-bromo-3-(pyridine-4-yl)-[1,2,4]triazolo[4,3-a]pyridine was crystallized in the monoclinic space group P 21/c with a = 14.3213(11), b = 6.9452(4) (4), c = 12.6860(8)Å, β = 100.265(6)°, V = 1241.62(14)Å3, Z = 4, and R = 0.0561