Potassium Persulfate Promoted the One-Pot and Selective <i>Se</i>-Functionalization of Pyrazoles under Acidic Conditions

Our research presents selective direct selenylation at the C-4 pyrazole ring using K₂S₂O₈ as an oxidant under simple and mild conditions. This elegant synthesis involves the one-pot method under acidic conditions, thus minimizing reaction steps and waste generation. This innovative method allowed us to create a library of 4-selanylpyrazoles in good to excellent yields. Furthermore, with slight changes in the protocol, we describe the synthesis of the unprecedented 4,5-bis-selanylpyrazole. The selectivity of the new insertion of organoselenium into the pyrazole core was demonstrated by several ¹H and ⁷⁷Se NMR experiments.