Palladium-catalyzed chelation-assisted ortho-tetra-acetoxylation of 1,3-diarylpyrazoles and 1,3-diarylindazoles

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.

Palladium catalyzed C–H bond acetoxylation: isoxazolinyl as a directing group

Pd(OAc)₂-catalyzed acetoxylations of 3-aryl or 3-alkyl groups mounted on a 2-isoxazoline ring were studied. Substituent effect on reactivity and regioselectivity was examined. The acetoxylation was applied to the synthesis of useful intermediates.

Pd-catalyzed direct oxidative mono-aroyloxylation of O-aralkyl substituted acetoxime ethers

A highly site-selective palladium-catalyzed ortho-mono-aroyloxylation of O-aralkyl substituted acetoxime ethers via direct Csp²–H bond activation has been developed with simple exo-acetoxime as a directing group.

Late-stage diversification of biologically active pyridazinones via a direct C-H functionalization strategy

Divergent C-H functionalization reactions (arylation, carboxylation, olefination, thiolation, acetoxylation, halogenation, naphthylation) using a pyridazinone moiety as an internal directing group were successfully established. This approach offers a late-stage, ortho-selective diversification of a biologically active pyridazinone scaffold. Seven series of novel pyridazinone analogues were synthesized conveniently as the synthetic precursors of potential sortase A (SrtA) inhibitors.