There are numerous ways to synthesize substituted pyrazoles, the most common being the addition of hydrazines to 1,3-diketones.  In some cases, this reaction suffers from the challenging synthesis of cyclization precursors or from the generation of undesired regioisomers.  The condensation of nitrilimines with tethered alkenes and alkynes to give annulated pyrazoles has gained favor in recent years due to the regiospecificity of the reaction.  The synthesis of 2 series of bicyclic pyrazoles via 3+2 dipolar cycloadditions of nitrilimines with alkynes is discussed.

Synthesis of substituted bicyclic pyrazoles via nitrilimine-alkyne cycloadditions

244th National Meeting (2012)

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