Regioselective synthesis of 3H-Pyrazoles bearing difluoromethyl phosphonate group

A catalyst-and solvent-free 1,3-dipolar cycloaddition of a bench-stable diazo reagent, 2-diazo-1,1,3,3,3-pentafluoropropyl phosphonate with selected alkynes is reported. As a result, a series of novel 3H-pyrazoles bearing difluoromethyl phosphonate unit is obtained in moderate-to-excellent yields. This approach provides an efficient and easy route to this valuable class of compounds.