The role of hypervalent iodine(iii) reagents in promoting alkoxylation of unactivated C(sp3)-H bonds catalyzed by palladium(ii) complexes

Organohypervalent heterocycles

This review summarizes the structural and synthetic aspects of heterocyclic molecules incorporating an atom of a hypervalent main-group element. The term "hypervalent" has been suggested for derivatives of main-group elements with more than eight valence electrons, and the concept of hypervalency is commonly used despite some criticism from theoretical chemists. The significantly higher thermal stability of hypervalent heterocycles compared to their acyclic analogs adds special features to their chemistry, particularly for bromine and iodine. Heterocyclic compounds of elements with double bonds are not categorized as hypervalent molecules owing to the zwitterionic nature of these bonds, resulting in the conventional 8-electron species. This review is focused on hypervalent heterocyclic derivatives of nonmetal main-group elements, such as boron, silicon, nitrogen, carbon, phosphorus, sulfur, selenium, bromine, chlorine, iodine(III) and iodine(V).

Experiment and Computational Study on Pd-Catalyzed Methoxyiminoacyl-Directed γ-Alkoxylation of Alkylamides

The direct alkoxylation of amides has been accomplished via methoxyiminoacyl (MIA)-mediated Pd-catalyzed C-H functionalization. A diverse array of alkylamide substrates is amenable to this protocol, providing γ-C(sp3)-alkoxylation of alkylamide derivatives with good to high efficiency. Two aspects of the research were completed to explore the reaction mechanism. On the one hand, the result of the kinetic isotopic effect experiment and control experiment indicated that reductive elimination is a rate-limiting step. On the other hand, density functional theory calculations demonstrated that a concerted Sn2 reductive elimination mechanism pathway is prior. Finally, the MIA group could be efficiently hydrogenated and protected in a one-pot procedure, which provides a short synthetic route to γ-methoxy amino acid derivatives.

DFT Studies on the Mechanisms of Carboamination/Diamination of Unactivated Alkenes Mediated by Pd(IV) Intermediates

Density functional theory (DFT) calculations have been employed to investigate the mechanism of carboamination and diamination of unactivated alkenes mediated by Pd(IV) intermediates. Both reactions share a common Pd(IV) intermediate, serving as the starting point for either the carboamination or the diamination pathway. The formation of this Pd(IV) intermediate encompasses a transition state that substantially impacts the turnover frequency (TOF) of catalytic cycles, with an apparent activation free-energy barrier of 26.1 kcal mol-1. Carboamination of unactivated alkenes proceeds through the coordination of a toluene molecule, C-H activation, inner reductive elimination, and the separation of the carboamination product from this intermediate, while diamination of unactivated alkenes involves the formation of the ion nucleophile, SN2 attack, and the separation of the diamination product. A comparison of the free-energy profiles for carboamination and diamination of unactivated alkenes can elucidate the origin of the chemoselectivity, and Bader's atoms in molecules (AIM) wave function analyses have been performed to analyze the contributions of the outer C-N bonding in the diamination process.

Transition Metal-Catalyzed C-H Functionalization Through Electrocatalysis

Electrochemically promoted transition metal-catalyzed C-H functionalization has emerged as a promising area of research over the last few decades. However, development in this field is still at an early stage compared to traditional functionalization reactions using chemical-based oxidizing agents. Recent reports have shown increased attention on electrochemically promoted metal-catalyzed C-H functionalization. From the standpoint of sustainability, environmental friendliness, and cost effectiveness, electrochemically promoted oxidation of a metal catalyst offers a mild, efficient, and atom-economical alternative to traditional chemical oxidants. This Review discusses advances in the field of transition metal-electrocatalyzed C-H functionalization over the past decade and describes how the unique features of electricity enable metal-catalyzed C-H functionalization in an economic and sustainable way.

Palladium-Catalyzed Organic Reactions Involving Hypervalent Iodine Reagents

The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry, resulting in a broad variety of useful organic molecules. These chemicals have potential uses in various functionalization procedures due to their non-toxic and environmentally friendly properties. As they are also strong electrophiles and potent oxidizing agents, the use of hypervalent iodine reagents in palladium-catalyzed transformations has received a lot of attention in recent years. Extensive research has been conducted on the subject of C—H bond functionalization by Pd catalysis with hypervalent iodine reagents as oxidants. Furthermore, the iodine(III) reagent is now often used as an arylating agent in Pd-catalyzed C—H arylation or Heck-type cross-coupling processes. In this article, the recent advances in palladium-catalyzed oxidative cross-coupling reactions employing hypervalent iodine reagents are reviewed in detail.

Current state and future perspectives of cytochrome P450 enzymes for C–H and C=C oxygenation

Cytochrome P450 enzymes (CYPs) catalyze a series of C–H and C=C oxygenation reactions, including hydroxylation, epoxidation, and ketonization. They are attractive biocatalysts because of their ability to selectively introduce oxygen into inert molecules under mild conditions. This review provides a comprehensive overview of the C–H and C=C oxygenation reactions catalyzed by CYPs and the various strategies for achieving higher selectivity and enzymatic activity. Furthermore, we discuss the application of C–H and C=C oxygenation catalyzed by CYPs to obtain the desired chemicals or pharmaceutical intermediates in practical production. The rapid development of protein engineering for CYPs provides excellent biocatalysts for selective C–H and C=C oxygenation reactions, thereby promoting the development of environmentally friendly and sustainable production processes.

Oxidative Addition of a Hypervalent Iodine Compound to Cycloplatinated(II) Complexes for the C-O Bond Construction: Effect of Cyclometalated Ligands

The complex [PtMe(Obpy)(OAc)₂(H₂O)], 2a, Obpy = 2,2'-bipyridine N-oxide, is prepared through the reaction of [PtMe(Obpy)(SMe₂)], 1a, by 1 equiv of PhI(OAc)₂ via an oxidative addition (OA) reaction. Pt(IV) complex 2a attends the process of C-O bond reductive elimination (RE) reaction to form methyl acetate and corresponding Pt(II) complex [Pt(Obpy)(OAc)(H₂O)], 3a. The kinetic of OA and RE reactions are investigated by means of different spectroscopies. The obtained results show that the reaction rates of OA step of 1a are faster than its analogous complex [PtMe(ppy)(SMe₂)], 1b, ppy = 2-phenylpyridine. The density functional theory (DFT) calculations signify that the OA reaction initiated by a nucleophilic attack of the platinum(II) central atom of 1b on the iodine(III) atom while it had commenced by a nucleophilic substitution reaction of coordinated SMe₂ in 1a with a carbonyl oxygen atom of PhI(OAc)₂. Our calculation revealed that the key step for 1a is an acetate transfer from the I(III) to Pt(II) through a formation of square pyramidal iodonium complex. This can be attributed to the more electron-withdrawing character of Obpy ligand than to ppy which reduces the nucleophilicity of Pt atom in 1a. Furthermore, 2a with electron-withdrawing Obpy ligand prone to C-O bond formation faster than complex [PtMe(ppy)(OAc)₂(H₂O)], 2b, with an electron-rich ppy ligand which conforms to the anticipation that REs occur faster on electron-poor metal centers.

Synthesis of Indole-Fused Six-, Seven-, or Eight-Membered N,O-Heterocycles via Rhodium-Catalyzed NH-Indole-Directed C-H Acetoxylation/Hydrolysis/Annulation

We report herein the facile synthesis of indole-fused six-, seven-, or eight-membered N,O-heterocycles through rhodium-catalyzed C-H acetoxylation/hydrolysis/annulation. The notable features of this method include C-H acetoxylation using NH-indole as the intrinsic directing group, high functional group compatibility, and construction of indole-fused medium-sized rings.