Palladium-catalyzed regioselective synthesis of 2(2 $$^{\prime }$$ ′ -biphenyl)benzimidazoles through C–H activation

Hypervalent iodine promoted ortho diversification: 2-aryl benzimidazole, quinazoline and imidazopyridine as directing templates

The mild and efficient palladium-catalyzed ortho C(sp²)-H diversification of (NH)-free 2-substituted benzimidazole, quinazoline, and imidazopyridine is reported using hypervalent iodine as the key reagent. Acetoxy, aryl, iodide and nitro functional groups were introduced on the same substrate by simply shifting the reaction conditions in the presence of inorganic additives (Cs₂CO₃, I₂, NaNO₂) and the hypervalent iodine reagent (diacetoxyiodo)benzene (PIDA) under aerobic conditions. The combination of NaNO₂ with PIDA was successfully employed in Pd-catalyzed C-H bond nitration to achieve a library of nitrated 1,3 N-heterocycles. This versatile ortho C(sp²)-H activation strategy features operational simplicity, short reaction times, and ample substrate possibilities, it requires no ligands or silver salts as additives, and it shows good tolerance of oxidation prone functional groups.

Quinoxaline as an integrated directing group in palladium-catalyzed ortho-C–H bond arylation of the aryl unit of 2-arylquinoxalines

ortho-Directed arylation of the C(sp²)–H bond of 2-arylquinoxalines with a broad range of aryl bromides was achieved using phosphine-free Pd(OAc)₂.

Palladium(II)-catalyzed sequential C-H arylation/aerobic oxidative C-H amination: one-pot synthesis of benzimidazole-fused phenanthridines from 2-arylbenzimidazoles and aryl halides

Starting from 2-arylbenzimidazoles and aryl halides, an efficient palladium-based catalytic method for the synthesis of benzimidazole-fused phenanthridines has been developed. This reaction sequence comprises intermolecular C-H arylation and intramolecular aerobic oxidative C-H amination, involving the rupture of two C-H bonds, one C-X bond, and one N-H bond in one pot. The Pd(II)-Pd(IV)-Pd(II) and Pd(II)-Pd(0)-Pd(II) catalytic cycles work together under the reported conditions to generate phenanthridines with diverse substituents.