Chemoselectivity of thiophene dicarboxylate towards hydrazine hydrate: Synthesis of some new bis heterocycles from thiophene monocarbohydrazide

摘要: Chemoselectivity of C5-carbethoxy function over that C3-carbethoxy the thiophene dicarboxylate towards nucleophilic attack hydrazine hydrate has been evidenced by exclusive formation monocarbohydrazide i.e. ethyl 2-amino-5-(hydrazinocarbonyl)-4-methylthiophene-3-carboxylate and this was reacted separately with acetylacetone, cyanogen bromide, acetonylacetone CS2 in ethanolic potassium hydroxide solution to furnish corresponding derivatives 3,5-dimethylpyrazole, 5-aminooxadiazole, 2,5-dimethylpyrrole 5-thiooxadiazole respectively. Thiophene converted hydrazone reacting p-chlorobenzaldehyde isatin. The also thiosemicarbohydrazide derivatives, which then cyclised POCl3 afford thiadiazole derivatives. structures all newly synthesized compounds were elucidated on basis their spectral analytical data sc...