Pyridine‐2(1<i>H</i>)‐thiones: Versatile Precursors for Novel Pyrazolo[3,4‐<i>b</i>]pyridine, Thieno[2,3‐<i>b</i>]pyridines, and Their Fused Azines

Abstract

Pyridine‐2(1 H )‐thiones were prepared and reacted with several active halogenated reagents to afford novel thieno[2,3‐ b ]pyridines in excellent yields. Thieno[2,3‐ b ]pyridine‐2‐carbohydrazide derivative was prepared by the reaction of either ethyl 2‐((3‐cyanopyridin‐2‐yl)thio)acetate derivative or thieno[2,3‐ b ]pyridine‐2‐carboxylate derivative with hydrazine hydrate. On the other hand, the reaction of either pyridine‐2(1 H )‐thione or ethyl 2‐((pyridin‐2‐yl)thio)acetate derivative with hydrazine hydrate afforded the corresponding 1 H ‐pyrazolo[3,4‐ b ]pyridine derivative. Thieno[2,3‐ b ]pyridine derivatives reacted with several reagents to afford the corresponding pyrimidine‐4(3 H )‐ones and [1,2,3]triazin‐4‐(3 H )‐one. Moreover, 2‐carbohydrazide derivative reacted with β‐dicarbonyl reagents to give 2‐((3‐methyl‐1 H ‐pyrazol‐1‐yl)carbonyl)thienopyridines. The structure of the target molecules is elucidated using elemental analyses and spectral data.