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-hydrazonop hosphine oxides 2 to isocyanates and isothiocyanates to give functiona lized amides 3 and 7. Subsequent cyclization of 3 with phosphorus oxyc hloride in the presence of triethylamine afforded pyrazoles derived fr om phosphine oxides 1 and phosphine sulphides 8. Substituted heterocyc les 1 can also be obtained in ''one pot'' reaction from phosphine oxid es 2 when these compounds are metallated followed by addition of isocy anates and phosphorus oxychloride.