An efficient and general strategy for the synthesis of 4-phosphorylated pyrazoles from beta-hydrazono phosphine oxides.

A simple and efficient synthesis of aminopyrazoles substituted with a phosphino oxide and sulphide groups in the 4-position 1 is described. The key step is a regioselective addition of lithiated beta-hydrazonophosphine oxides 2 to isocyanates and isothiocyanates to give functionalized amides 3 and 7. Subsequent cyclization of 3 with phosphorus oxychloride in the presence of triethylamine afforded pyrazoles derived from phosphine oxides 1 and phosphine sulphides 8. Substituted heterocycles 1 can also be obtained in ''one pot'' reaction from phosphine oxides 2 when these compounds are metallated followed by addition of isocyanates and phosphorus oxychloride.