Electrochemically promoted site-selective selenylation at the C-4 position of pyrazolones.

The late-stage functionalization of drug molecules represents a significant advancement in medicinal chemistry. We herein describe an electrochemical strategy for site-selective selenylation at the C-4 position of pyrazolones under transition-metal- and oxidant-free conditions. This method exhibits broad substrate scope, accommodating a variety of pyrazolones and selenium sulfonates, and delivers the corresponding products in up to 92% yield. Using selenium sulfonates as selenylating reagents, this approach provides a practical route for introducing selenium into bioactive pyrazolone scaffolds, demonstrating considerable potential in drug diversification.