Synthesis of 4-amino-5-(3-chlorobenzo[b]thien-2-yl)-3-mercapto-1,2,4- triazolo[3,4-b][1,3,4]thiadiazoles and triazolo[3,4,b][1,3,4]thiadiazines under classical and microwave conditions

Abstract

Conventional heating and microwave (MW) irradiation of 3-chloro-2- chlorocarbonylbenzo[b]thiophene (1) with hydrazine hydrate afforded the corresponding hydrazide 2. Potassium dithiocarbazate 3 was cyclized with hydrazine to afford 4-amino-5-(3-chlorobenzo[b]thien-2-yl)-3-mercapto-1,2,4- triazole (4). Treatment of 4 with formic acid afforded the N-formyl derivative 5 and not the cyclized product 6, but with acetic anhydride afforded the triazolothiadiazole 8. Reaction of 4 with carbon disulfide in pyridine afforded 3-(3-chlorobenzo[b]thien-2-yl)-1,2,4-triazolo[3,4-b][1,3,4]thiadiazol-6(5H) thione (9) which was alternatively obtained by fusion of 4 with thiourea. Fusion of 4 with urea gave 6-amino-3-(3-chlorobenzo[b]thien-2-yl)-1,2,4-triazolo [3,4-b][1,3,4]thiadiazol-6(5H)one (11). The 3-(3-chlorobenzo[b]thien-2-yl)-5H-1, 2,4-triazolo[3,4-b][1,3,4]thiadiazino[5,6-b]quinoxaline (12) was synthesized by reaction of 4 with 2,3-dichloroquinoxaline. Simultaneous deamination and dethiolation of 4 gave 14. Carboxymethylation of 4 afforded 15 and not the cyclized compound 16. Carbethoxymethylation of 4 in presence of triethylamine afforded the thioalkylated product 17 and in presence of sodium ethoxide gave two 1,2,4-triazolo[1,3,4]thiadiazine derivatives 16 and 18. Better yields and shorter reaction times were achieved using MW. ©ARKAT.