Studies with Polyfunctionally Substituted Heterocycles: New Synthesis of Pyrido[5′, 4′:2,3][1,3,4]oxadiazolo[3,2‐a]pyridine; Pyridazine; 1,3,4‐Oxadiazote; and Pyrazolo[1,5‐a]Pyrimidine Derivatives

Cyanoacetohydrazide 1a reacts with 2‐arylhydrazoketons 2a,b and 3a,b in refluxing ethanol to yield pyrido[5′,4′:2,3][1,3,4]oxadiazolo[3,2‐a]pyridine and pyridazine derivatives; in the absence of solvent pyrazolo[1,5‐a]pyrimidine derivatives were obtained. The reaction of 2a,b and 3a,b will) benzoylhydrazine afforded 1,3,4‐oxadiazole and pyrazole derivatives.