Lewis Acid/Oxidant as Rapid Regioselective Halogenating Reagent System for Direct Halogenation of Fused Bi‐/Tri‐cyclic Hetero‐Aromatic Congeners via C ( s p 2 ) −H bond Functionalization

Herein, we report the identification of new and fast halogenating reagent system consisting of Lewis acid AlX 3 [X=Cl, Br, I] as a halogen source in the presence of tert ‐butyl hydroperoxide (TBHP) which has been utilized for the direct regioselective halogenation on various fused bi‐/tri‐cyclic hetero‐aromatic congeners 3 a – q , 7 a – d , 8  and 9   viaC( sp 2 ) −H bond functionalization. The operationally simple protocol is quite fast and does not require the external halogenation source at 110 °C in 20–60 minutes and furnished halogenated fused heterocycles 4 a – p , 5 a – k , 6 a – l , 10 a – i , 11 a , 12 a – b in up to 96% yields. The gram‐scale synthesis, wide substrate scope, functional group tolerance, control experiments and application to further derivatization/functionalization for C−C bond formation further highlights the versatility of the developed methodology as well as the compatibility of the new catalyst. The combination of Lewis acid (AlX 3 ) as a halogen source and TBHP (oxidant) as a halogenating reagent system is the first account for the direct regioselective halogenation of several fused bi‐/tri‐cyclic hetero‐aromatic congeners viaC( sp 2 ) −H bond functionalization.