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

Pyridine-2(1H)-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(1H)-thione or ethyl 2-((pyridin-2-yl)thio)acetate derivative with hydrazine hydrate afforded the corresponding 1H-pyrazolo[3,4-b]pyridine derivative. Thieno[2,3-b]pyridine derivatives reacted with several reagents to afford the corresponding pyrimidine-4(3H)-ones and [1,2,3]triazin-4-(3H)-one. Moreover, 2-carbohydrazide derivative reacted with β-dicarbonyl reagents to give 2-((3-methyl-1H-pyrazol-1-yl)carbonyl)thienopyridines. The structure of the target molecules is elucidated using elemental analyses and spectral data.