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Synthesis of 3H-pyrazoles

Recent Literature

FeCl3 mediates a propargylic substitution of tertiary propargylic alcohols with p-toluenesulfonyl hydrazide. A subsequent cyclization under mild conditions in the presence of iodine enables an efficient and rapid synthesis of iodo-3H-pyrazoles with a wide substrate scope and in high yields.
X.-T. Liu, Z.-C. Ding, L-C. Ju, Z.-N. Tang, F. Wu, Z.-P. Zhan, Synlett, 2017, 28, 620-624.

A simple, highly efficient, 1,3-dipolar cycloaddition of diazo compounds and alkynyl bromides gives 3,5-diaryl-4-bromo-3H-pyrazoles or the isomerization products 3,5-diaryl-4-bromo-1H-pyrazoles in good yields. The diazo compounds and alkynyl bromides were generated in situ from tosylhydrazones and gem-dibromoalkenes, respectively. The reaction system exhibited high regioselectivity and good functional group tolerance.
Q. Sha, Y. Wei, Synthesis, 2013, 45, 413-420.