A Traceless Heterocyclic Amine Mediator in Regioselectivity-Switchable Formal [1 + 2 + 2] Cycloaddition Reaction to 1,3,4- and 1,4,5-Trisubstituted Pyrazoles.

Switchable multicomponent reactions have been attractive tools for the construction of compound libraries with skeleton diversity and complexity by slightly changing the reaction conditions. Described herein is a regioselectivity-switchable formal [1 + 2 + 2] cycloaddition reaction from difluoroalkyl compounds, enaminones, and RNHNH, ultimately using 1-methylindazol-3-amine as a traceless mediator to switch the inherent regioselectivity of 1,3,4-trisubstituted pyrazole formation to 1,4,5-trisubstituted pyrazoles. Remarkable features of this work include mild conditions, simple operation, and broad scopes.