Novel Vilsmeier-type methylenation for synthesis of dipyrazolylmethane derivatives using formamide or N-methylformamide

A novel Vilsmeier-type methylenation for synthesis of dipyrazolylmethanes was developed by reacting pyrazolones with formamide or N-methylformamide in the presence of phosphorous oxychloride POCl₃ coupling agent. This method can efficiently provide a series of dipyrazolylmethane derivatives as the main products in excellent yields without the formylated products. Our experimental result was different with the classical Vilsmeier-type reaction.