DABCO-Promoted Synthesis of Pyrazoles from Tosylhydrazones and Nitroalkenes.

An efficient synthesis of pyrazoles from tosylhydrazones and nitroalkenes was developed. In comparison with the previously reported 1,3-dipolar cycloaddition reaction of diazo compounds with electron-deficient alkenes or alkynes, this methodology proceeded with a sequential Baylis–Hillman/intramolecular cyclization mechanism and a variety of reversed regioselectivity products were prepared in good yields.