Thermocontrolled Radical Nucleophilicity vs Radicophilicity in Regiodivergent C–H Functionalization

The temperature-dependent switching behavior of the saccharin radical is demonstrated, enabling the regiodivergent C3–H and C7–H functionalization of quinoxalin-2(1H)-ones. The saccharin radical was generated through N–Br bond cleavage in N-bromosaccharin (NBSA) and was observed to transition between radical and radicophile roles. At −10 °C, it was utilized as a radicophile, resulting in 100% C3-amination, while at +35 °C, it acted as a radical, leading to exclusive C7-bromination. Radical nucleophilicity was controlled by temperature modulation.