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.