Synthesis of novel pyrazolo[3,4‐ d ]pyridazine, pyrido[1,2‐ a ]benzimidazole, pyrimido[1,2‐ a ]benzimidazole and triazolo[4,3‐ a ]pyrimidine derivatives

4‐Acetyl‐5‐methyl‐1‐phenyl‐1 H ‐pyrazole reacts with dimethylformamide dimethylacetal (DMF‐DMA) to afford the corresponding ( E )1‐(5‐methyl‐1‐phenyl‐1 H ‐pyrazol‐4‐yl)‐3‐( N,N ‐dimethylamino)‐2‐propen‐1‐one. The latter product undergoes regioselective 1,3‐dipolar cycloaddition with nitrilimines and nitrile oxides to afford the novel 3‐aroyl‐4‐(5‐methyl‐1‐phenyl‐1 H ‐pyrazol‐4‐yl)carbonyl‐1‐phenylpyrazole and 3‐aroyl‐4‐(5‐methyl‐1‐phenyl‐1 H ‐pyrazol‐4‐yl)carbonyl isoxazole derivatives, respectively. It reacts also with 1 H ‐benzimidazole‐2‐acetonitrile, 2‐aminobenzimidazole and 3‐amino‐1,2,4‐triazole to afford the novel pyrido[1,2‐ a ]benzimidazole, pyrimido[1,2‐ a ]benzimidazole and the triazolo[4,3‐ a ]pyrimidine derivatives, respectively. The reaction of 3‐aroyl‐4‐(5‐methyl‐1‐phenyl‐1 H ‐pyrazol‐4‐yl) carbonyl‐1‐phenylpyrazole derivatives with hydrazine hydrate led to a new pyrazolo[3,4‐ d ]pyridazine derivatives.