1,2,4-Triazolo[4,3-a]pyridin-3(2H)-one

109-09-1

563-41-7

6969-71-7

General procedure for the synthesis of [1,2,4]triazolo[4,3-a]pyridin-3-(2H)-one from 2-chloropyridine and aminourea hydrochloride: 2-chloropyridine (5.0 g, 44.03 mmol), aminourea hydrochloride (9.8 g, 88.06 mmol), and 2-ethoxyethanol (15 mL) were mixed and heated to reflux. Concentrated hydrochloric acid (0.1 mL dissolved in 1 mL of 2-ethoxyethanol) was slowly added to the reaction mixture. The reaction was kept at reflux for 24 hours and subsequently cooled to about 60 °C and diluted with deionized water (15 mL). The resulting light yellow solid product was collected by filtration and washed with deionized water to afford the title compound (2.2 g, 51% yield). The melting point of the product was 235-240°C. 1H NMR (300 MHz, DMSO-d6) δ 6.51-6.60 (m, 1H), 7.05-7.22 (m, 2H), 7.80 (d, J=7.1 Hz, 1H), 12.45 (br, 1H, exchangeable with D2O); IR (KBr) ν 3173, 3098. 3048, 1717, 1634, 1536, 1348 cm-1; MS 136 (M+1).