Biginelli-Type Reaction from Pyrazole-iminium salts in a Reagent-Integrated Urea-Citric acid Eutetic Medium

Multicomponent reactions are powerful tools for the rapid assembly of structurally diverse heterocycles. Among them, the Biginelli reaction¹ remains one of the most valuable approaches for accessing 3,4-dihydropyrimidin-2(1H)-ones, privileged scaffolds in medicinal chemistry². Herein, we report a Biginelli-type cyclocondensation employing preformed pyrazole-derived iminium salts as electrophilic partners in a urea–citric acid eutectic medium³. The eutectic system constitutes the sole urea source required for heterocycle formation, integrating solvent and reagent functions within a single reaction platform. The developed methodology provides straightforward access to a previously unreported pyrazole-functionalized 3,4-dihydropyrimidin-2(1H)-ones in moderate to good yields. The substrate scope of this transformation is currently under investigation. This work introduces pyrazole-derived iminium salts as competent electrophilic partners for Biginelli-type cyclocondensations while demonstrating the potential of reagent-integrated eutectic media as multifunctional platforms for multicomponent heterocycle synthesis.