Synthesis of 3-substituted 1,2,4-triazolo (3,4-b) benzothiazoles

3-Hydrazino 1,2,4-triazolo (3,4-b) benzothiazole 1 on heating with methyl chloroformate, acetic anhydride and benzoyl chloride separately afforded 3-(N-carbomethoxy) hydrazino 2, 3-(1,2-diacetyl) hydrazino 5 and 3-(N-benzoyl) hydrazino-1,2,4-triazolo (3,4-b) benzothiazole 7 respectively. Compound 1 on treatment with acrylonitrile in the presence of pyridine yielded 3-propane nitrile derivative 8 which on refluxing with dil hydrochloric acid afforded 3-(pyrazol-5-one-1-yl)-1,2,4-triazolo (3,4-b) benzothiazole 9. N-[3-amino-1,2,4-triazolo (3,4-b) benzothiazole] phthalimide 10 was obtained by heating 1 with phthalic anhydride, 1-[3'-(1,2,4) triazolo (3,4-b) benzothiazolyl]3,5-dialkyl/diaryl-1,2,4-1H-triazoles 11a,b,c were prepared by condensing 1 with alkyl and aryl nitriles. Reaction of I with ethyl acetoacetate and acetyl acetone afforded 1-[3'-(1,2,4)-triazolo (3,4-b) benzothiazolyl]-3-ethoxy-5-methyl pyrazole 12 and 1-[3'-(1,2,4)triazolo (3,4-b) benzothiazolyl]-3,5-dimethyl pyrazole 13 respectively. But condensation of 1 with diethyl oxalate resulted in the formation of altogether different compound, 3-aminoformyl-1,2,4-triazolo (3,4-b) benzothiazole 15. All newly synthesized compounds were characterized on the basis of elemental and spectral analysis.