Novel synthesis and ring closure reactions of 3-hydrazino-1,2,4-triazolo[3,4-<i style="">b</i>]benzothiazole

Abstract

3-Hydrazino-1,2,4-triazolo[3,4-<i style="">b</i>]benzothiazole <b style="">2 </b>is prepared by heating 3-chloro-1,2,4-triazino[3,4-<i style="">b</i>]benzothiazole-4(<i style="">H</i>)-one <b style="">1 </b>with hydrazine hydrate. This transformation takes place with decarbonylation resulting in ring contraction and simultaneous replacement of chlorine by hydrazino group. Compound<b style=""> 2</b> on heating independently with urea and carbon disulphide in the presence of alkali gave 3'-hydroxy <b style="">3 </b>and 3'-mercapto-1,2,4-triazolo[4',5':1,5]-1,2,4-triazolo[3,4-<i style="">b</i>] benzothiazole <b style="">4 </b>respect­ively.<b style=""> </b>Treatment of cold solution of <b style="">2</b> in phosphoric acid with sodium nitrite solution affords 1,2,3,4-tetra­zolo[1',5':1,5]-1,2, 4-triazolo[3,4-<i style="">b</i>]benzothiazole <b style="">5</b>. 3'-Aryl-1, 2, 4-triazolo[4',5':1,5]-1, 2, 4-triazolo[3,4-<i style="">b</i>] benzothiazoles <b style="">7a-e </b>have been also prepared by the reaction of <b style="">2</b> with aryl aldehydes in the presence of acetic acid.