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.