Sulfonylpyrazoles via Base-Mediated Reaction of Diazosulfone with Nitroalkenes

Significance

Based on a previous report (R. Muruganantham, S. M. Mobin, I. N. N. Namboothiri Org. Lett. 2007, 9, 1125), the synthesis of sulfonylpyrazoles 3 from α-diazo-β-ketosulfone 2 and nitroalkene 1 via a 1,3-dipolar cycloaddition is reported. Optimized conditions require the presence of nucleophilic base such as NaOMe to achieve the deacylation of 2, which precedes the [2+3] ­cycloaddition. Various aryl, heteroaryl, alkyl, hydroxymethyl and hydrazinyl pyrazoles were thus prepared by the appropriate choice of nitroalkene. However, when α,β-disubstituted nitroethylenes are used, the synthesis of the corresponding 3,4,5-trisubstituted pyrazoles 3 needed longer time and they were formed in lower yields. The ­potent analgesic agent withasomnine (H.-B. Schröter, D. Neumann, A. R. Katritzky, F. J. ­Swinbourne Tetrahedron 1966, 22, 2895) was prepared by this methodology in five steps.