Activation of C–Br Bond of CBr4 and CBrCl3 Using 9‑Mesityl-10-methylacridinium Perchlorate Photocatalyst

Herein, we report the activation of the C–Br bond of CBrX3 (X = Cl, Br) using 9-mesityl-10-methylacridinium perchlorate as a visible-light (12W blue LED, 450–455 nm) photocatalyst for the synthesis of gem-dihaloenones from terminal alkynes. An electron transfer from CBrX3 to Mes-Acr-MeClO4 led to the formation of •+CBrX3 which subsequently resulted in the intermediate +CX3. Next, C–C cross-coupling of +CX3 with terminal alkynes was the key path to obtain the gem-dihaloenones. Radical trapping experiments with TEMPO, BHT, and Stern–Volmer quenching studies helped to understand that the reaction proceeded via the SET mechanism.