PdCl2 and N-hydroxyphthalimide co-catalyzed C(sp2)-H hydroxylation by dioxygen activation

Direct hydroxylation of benzene to phenol with molecular oxygen over vanadium oxide nanospheres and study of its mechanism

Direct hydroxylation of benzene to phenol using molecular oxygen is a green route with high atom economy but still a great challenge when compared with the existing method of production.

Transition metal-catalyzed C–H bond functionalizations by the use of diverse directing groups

In this review, a summary of transition metal-catalyzed C–H activation by utilizing the functionalities as directing groups is presented.

Palladium-catalyzed ortho-acyloxylation of N-nitrosoanilines via direct sp2 C–H bond activation

The palladium-catalyzed N-nitroso-directed ortho-acyloxylation of N-nitrosoanilines has been demonstrated via sp² C–H activation with PhI(OAc)₂ as the oxidant and Ac₂O/AcOH (1 : 1) or C₂H₅CO₂H as the reaction medium.

Autoinductive thiolation/oxygenation of alkenes at room temperature

Spontaneous O₂ fixation by just mixing activated alkenes and thiols at room temperature is rationally demonstrated.

Palladium catalyzed Csp2–H activation for direct aryl hydroxylation: the unprecedented role of 1,4-dioxane as a source of hydroxyl radicals

Direct aryl hydroxylation has been achieved via palladium-catalysed C_sp2–H activation using versatile directing groups through unprecedented hydroxyl transfer from 1,4-dioxane.

Cetyl alcohol mediated synthesis of CuCr2O4 spinel nanoparticles: a green catalyst for selective oxidation of aromatic C–H bonds with hydrogen peroxide

We report here cetyl alcohol-promoted synthesis of spherical CuCr₂O₄ spinel nanoparticles with almost uniform morphology, prepared hydrothermally.

Chloroacetate-promoted selective oxidation of heterobenzylic methylenes under copper catalysis

The efficient selective oxidation and functionalization of C-H bonds with molecular oxygen and a copper catalyst to prepare the corresponding ketones was achieved with ethyl chloroacetate as a promoter. In this transformation, various substituted N-heterocyclic compounds were well tolerated. Preliminary mechanistic investigations indicated that organic radical species were involved in the overall process. The N-heterocyclic compounds and ethyl chloroacetate work synergistically to activate C-H bonds in the methylene group, which results in the easy generation of free radical intermediates, thus leading to the corresponding ketones in good yields.

Palladium Catalyzed Aryl C-H Amination with O2 via In Situ Formation of Peroxide-Based Oxidant(s) from Dioxane

(DAF)Pd(OAc)2 (DAF = 4,5-diazafluorenone) catalyzes aerobic intramolecular aryl C-H amination with N-benzenesulfonyl-2-aminobiphenyl in dioxane to afford the corresponding carbazole product. Mechanistic studies show that the reaction involves in situ generation of peroxide species from 1,4-dioxane and O2, and the reaction further benefits from the presence of glycolic acid, an oxidative decomposition product of dioxane. An induction period observed for the formation of the carbazole product correlates with the formation of 1,4-dioxan-2-hydroperoxide via autoxidation of 1,4-dioxane, and the in situ-generated peroxide is proposed to serve as the reactive oxidant in the reaction. These findings have important implications for the palladium-catalyzed aerobic oxidation reactions conducted in ethereal solvents.

Aerobic oxidation of alkylaromatics using a lipophilic N-hydroxyphthalimide: overcoming the industrial limit of catalyst solubility

4,4'-(4,4'-Isopropylidenediphenoxy)bis(N-hydroxyphthalimide), which is a new lipophilic analogue of N-hydroxyphthalimide, can act as an effective catalyst in the aerobic oxidation of alkylaromatics under reduced amounts of polar cosolvent. The catalyst was selected on the basis of an in-depth study of the influence that substituents on the aromatic ring of N-hydroxyphthalimide exert on determining the NO-H bond dissociation energy (BDE). BDE values for a range of model molecules are calculated by DFT and measured by EPR spectroscopy. The new catalyst can be successfully employed in the aerobic oxidation of cumene, ethylbenzene, and cyclohexylbenzene, affording, in all cases, good conversions and high selectivity for the corresponding hydroperoxide. The effect of solvent, catalyst, and temperature has also been investigated.

Palladium-catalyzed ortho-alkoxylation of 2-aryl-1,2,3-triazoles

Palladium-catalyzed alkoxylation of 2-aryl-1,2,3-triazoles was described in the presence of various groups in the aromatic rings. In addition, some other directing groups of heterocycles containing nitrogen were explored.

Palladium-catalyzed hydroxylation of aryl and heteroaryl halides enabled by the use of a palladacycle precatalyst

A method for the hydroxylation of aryl and heteroaryl halides, promoted by a catalyst based on a biarylphosphine ligand tBuBrettPhos (L5) and its corresponding palladium precatalyst (1), is described. The reactions allow the cross-coupling of both potassium and cesium hydroxides with (hetero)aryl halides to afford a variety of phenols and hydroxylated heteroarenes in high to excellent yield.

Pd(II)-catalyzed C(sp2)-H hydroxylation with R2(O)P-coordinating group

A novel R2(O)P-directed Pd(II)-catalyzed C-H hydroxylation to synthesize various substituted 2'-phosphorylbiphenyl-2-ol compounds is described. Notably, the reaction operates under mild conditions and shows good functional group tolerance, high selectivity, and yield.

Ortho- and para-selective ruthenium-catalyzed C(sp2)-H oxygenations of phenol derivatives

Versatile ruthenium catalysts allowed for efficient direct oxygenations of aryl carbamates under remarkably mild reaction conditions. In addition to chelation-assisted C-H activation, the optimized ruthenium catalyst proved amenable to para-selective hydroxylations of anisoles without Lewis basic directing groups.