Selective sulfoxidation of thioethers and thioaryl boranes with nitrate, promoted by a molybdenum-copper catalytic system

The catalytic reduction of nitrate by molybdo-enzymes plays a central role in the global biological cycle of nitrogen. However, the use of nitrates as oxidants in synthetic organic chemistry is very limited and typically requires very strong acidic and other extreme reaction conditions. We have developed a highly chemoselective and efficient catalytic process for the sulfoxidation of thioethers and arylthioethers containing boronic acid or boronic ester functional groups, using nitrate salts as oxidants. This homogeneous catalytic reaction was carried out in acetonitrile, where the MoO(2)Cl(2)(OPPh(3))(2) complex 1 or a mixture of complex 1 with Cu(NO(3))(2) were used as catalysts. We examined the reaction mechanism using (1)H, (15)N, and (31)P NMR techniques and (18)O-labeled sodium nitrate (NaN(18)O(3)) and show that the thioethers are oxidized by nitrate, generating nitrite. Our work adds to the existing chemical transformations available for organoboron compounds, providing straightforward accessibility to a variety of new substrates that could be suitable for Suzuki cross-coupling chemistry.     

Transition Metal-Free Aromatic C−H,C−N,C−S and C−O Borylation

Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C−H and C−Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C−H and C−Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C−H, C−N, C−S, and C−O borylation transformations and provides insights to where further developments are required.     

Formyl MIDA Boronate: C1 Building Block Enables Straightforward Access to α-Functionalized Organoboron Derivatives

Formyl MIDA boronate has been known to be an elusive type of acylboronate that has not been obtained to date. In this work, an approach to the one-pot preparation and chemical transformations of formyl MIDA boronate were developed to provide new types of α-functionalized organoboron compounds. Among them are acylboronate reagents which present boron-substituted analogues of ynones and β-dicarbonyl compounds. The developed synthetic procedures, utilizing formyl MIDA boronate, are tolerant to diverse functional groups, making this reagent an advantageous C₁ building block for extending the scope of organoboron chemistry.     

Overcoming the limitations of lithiation chemistry for organoboron compounds with continuous processing

Quite a process: Recent pioneering reports establishing proof of concept for conducting lithiation chemistry to produce organoboron products in a continuous fashion are highlighted.     

Formyl MIDA Boronate: C1 Building Block Enables Straightforward Access to α‐Functionalized Organoboron Derivatives

Formyl MIDA boronate has been known to be an elusive type of acylboronate that has not been obtained to date. In this work, an approach to the one‐pot preparation and chemical transformations of formyl MIDA boronate were developed to provide new types of α‐functionalized organoboron compounds. Among them are acylboronate reagents which present boron‐substituted analogues of ynones and β‐dicarbonyl compounds. The developed synthetic procedures, utilizing formyl MIDA boronate, are tolerant to diverse functional groups, making this reagent an advantageous C₁ building block for extending the scope of organoboron chemistry.     

Oxidation Chemistry of DNA and p53 Tumor Suppressor Gene

The chemistry of DNA and its repair selectivity control the influence of genomic oxidative stress on the development of serious disorders such as cancer and heart diseases. DNA is oxidized by endogenous reactive oxygen species (ROS) in vivo or in vitro as a result of high energy radiation, non-radiative metabolic processes, and other consequences of oxidative stress. Some oxidations of DNA and tumor suppressor gene p53 are thought to be mutagenic when not repaired. For example, site-specific oxidations of p53 tumor suppressor gene may lead to cancer-related mutations at the oxidation site codon. This review summarizes the research on the primary products of the most easily oxidized nucleobase guanine (G) when different oxidation methods are used. Guanine is by far the most oxidized DNA base. The primary initial oxidation product of guanine for most, but not all, pathways is 8-oxoguanine (8-oxoG). With an oxidation potential much lower than G, 8-oxoG is readily susceptible to further oxidation, and the products often depend on the oxidants. Specific products may control the types of subsequent mutations, but mediated by gene repair success. Site-specific oxidations of p53 tumor suppressor gene have been reported at known mutation hot spots, and the codon sites also depend on the type of oxidants. Modern methodologies using LC–MS/MS for codon specific detection and identification of oxidation sites are summarized. Future work aimed at understanding DNA oxidation in nucleosomes and interactions between DNA damage and repair is needed to provide a better picture of how cancer-related mutations arise.     

Chemiluminescence of CdTe nanocrystals induced by direct chemical oxidation and its size-dependent and surfactant-sensitized effect

CdTe nanocrystals (NCs) capped with thioglycolic acid (TGA) were synthesized via a microwave-assisted method. The chemiluminescence (CL) of CdTe NCs induced by directly chemical oxidation and its size-depended and surfactant-sensitized effect in aqueous solution were then investigated. It was found that oxidants, especially hydrogen peroxide and potassium permanganate, could directly oxidize CdTe NCs to produce strong CL emission in basic conditions. The oxidized CL of CdTe NCs displayed size-dependent effect and its intensity increased along with increasing the sizes of the NCs. Moreover, the CL intensity could, if surfactants CTAB or beta-cyclodextrin were added to the above CL system, be sensitized to some degree. The sensitized CL induced by CTAB and beta-cyclodextrin is mainly contributing to the formation of aggregate nanostructure and the micellar micronanoenvironment, respectively. The possible oxidized CL mechanisms were further examined by means of photoluminescence spectra, CL spectra, and transmission electron microscopy studies. The CL properties of CdTe NCs not only will be helpful to study physical chemistry properties of semiconductor nanocrystals but also are expected to find use in many fields such as luminescence devices, bioanalysis, and multicolor labeling probes.     

Bystanding F+ oxidants enable selective reductive elimination from high-valent metal centers in catalysis

Reductive elimination from partially or completely oxidized metal centers is a vital step in a myriad of carbon-carbon and carbon-heteroatom bond-forming reactions. One strategy for promoting otherwise challenging reductive elimination reactions is to oxidize the metal center using a two-electron oxidant (that is, from M((n)) to M((n+2))). However, many of the commonly used oxidants for this type of transformation contain oxygen, nitrogen, or halogen moieties that are subsequently capable of participating in reductive elimination, thus leading to a mixture of products. In this Minireview, we examine the use of bystanding F(+) oxidants for addressing this widespread problem in organometallic chemistry and describe recent applications in Pd(II) /Pd(IV) and Au(I) /Au(III) catalysis. We then briefly discuss a rare example in which one-electron oxidants have been shown to promote selective reductive elimination in palladium(II)-catalyzed C-H functionalization, which we view as a promising future direction in the field.     

Synthesis and reactions of N-heterocyclic carbene boranes

Boranes are widely used Lewis acids and N-heterocyclic carbenes (NHCs) are popular Lewis bases, so it is remarkable how little was known about their derived complexes until recently. NHC-boranes are typically readily accessible and many are so stable that they can be treated like organic compounds rather than complexes. They do not exhibit "borane chemistry", but instead are proving to have a rich chemistry of their own as reactants, as reagents, as initiators, and as catalysts. They have significant potential for use in organic synthesis and in polymer chemistry. They can be used to easily make unusual complexes with a broad spectrum of functional groups not usually seen in organoboron chemistry. Many of their reactions occur through new classes of reactive intermediates including borenium cations, boryl radicals, and even boryl anions. This Review provides comprehensive coverage of the synthesis, characterization, and reactions of NHC-boranes.     

有机硼1,2-迁移化学概述

硼是一种重要的类金属元素,与人类生活息息相关。自从硼元素被引入到有机化合物中,化学家创造新物质的能力得到了革命性的提升。近年来,随着有机硼化学的蓬勃发展,该领域正在吸引越来越多的关注。本文重点介绍了硼元素的起源与结构,有机硼的1,2-迁移化学的特征及具体反应实例。     

Heteroelement Analogues of Benzoxaborole and Related Ring Expanded Systems

The review covers the chemistry of organoboron heterocycles structurally related to benzoxaboroles where one of the carbon atoms in a boracycle or a fused benzene ring is replaced by a heteroelement such as boron, silicon, tin, nitrogen, phosphorus, or iodine. Related ring expanded systems including those based on naphthalene and biphenyl cores are also described. The information on synthetic methodology as well as the basic structural and physicochemical characteristics of these emerging heterocycles is complemented by a presentation of their potential applications in organic synthesis and medicinal chemistry, the latter aspect being mostly focused on the promising antimicrobial activity of selected compounds.     

Metal‐Free and Redox‐Neutral Conversion of Organotrifluoroborates into Radicals Enabled by Visible Light

Converting organoboron compounds into the corresponding radicals has broad synthetic applications in organic chemistry. To achieve these transformations, various strong oxidants such as Mn(OAc)₃, AgNO₃/K₂S₂O₈, and Cu(OAc)₂, in stoichiometric amounts are required, proceeding by a single‐electron transfer mechanism. Established herein is a distinct strategy for generating both aryl and alkyl radicals from organotrifluoroborates through an S_H2 process. This strategy is enabled by using water as the solvent, visible light as the energy input, and diacetyl as the promoter in the absence of any metal catalyst or redox reagent, thereby eliminating metal waste. To demonstrate its synthetic utility, an efficient acetylation to prepare valuable aryl (alkyl) methyl ketones is described and applications to construct C?C, C?I, C?Br, and C?S bonds are also feasible. Experimental evidence suggests that triplet diacetyl serves as the key intermediate in this process.     

Poly(cyclodiborazane)s

This paper summarizes our recent works on the synthesis and properties of the organoboron polymers, especially poly(cyclodiborazane)s. The polymers consist of boron–nitrogen four-membered rings, and are highly stable against air and moisture. The obtained polymers exhibited interesting properties as a novel type of π-conjugated polymers with intramolecular charge transfer structure. Their stability and potential as functional materials would be important and informative both in industry and boron chemistry.     

碳硼烷化学发展之路

碳硼烷分子具有独特的笼状结构,能够表现出三维芳香性和稳定的物理化学性质,这使得碳硼烷不仅能够应用于有机硼化学及金属有机化学,而且在生物学、材料学等领域也有不错的应用前景。本文叙述了碳硼烷化学的发展历史、碳硼烷化合物的结构性质,并简要介绍了碳硼烷近年来在生物医学、发光材料以及催化剂领域的应用,希望对读者了解碳硼烷化学的新进展能够有所帮助。     

Pentafluorophenyl copper: aggregation and complexation phenomena, photoluminescence properties, and applications as reagent in organometallic synthesis

Recent advances in the chemistry of pentafluorophenyl copper are discussed, including the observation of strongly luminescent adducts with pyridine, the first successful structural characterization of an organocopper-arene complex, and the complexation with electron-rich transition metal complexes such as ferrocene derivatives. In addition, new applications in synthetic organometallic chemistry are discussed, which include the discovery of tin/copper exchange reactions for the preparation of organocopper compounds that are otherwise not readily accessible, and the selective transfer of the C(6)F(5) groups to boron to form catalytically active and electronically interesting organoboron polymers.     

Thianthrene 5-oxide as a probe for the electronic character of oxygen-transfer reactions: re-interpretation of experiments required

The electronic character of oxidants, i.e., whether they attack substrates in an electrophilic or nucleophilic way, has extensively been investigated using thianthrene 5-oxide (SSO) as probe. The SSO molecule has a sulfide group, which is attacked by electrophilic oxidants, and a sulfoxide moiety, which is oxidized by nucleophilic oxidants. This density-functional study has been carried out in order to gain insight into the origin of the chemo- and stereoselectivity of SSO oxidation. It has been found that the endo and exo stereoisomers of the thianthrene oxides interconvert via ring-inversion with moderate energy barriers. Thus, the stereoselectivity of SSO oxidation has to be interpreted with caution. Furthermore, a topological electron-density analysis of thianthrene 5-oxide reveals that there is an area of charge depletion at the sulfoxide group. The location of this area indicates that the attack of nucleophilic oxidants on SSO is sterically hindered. Therefore, the SSO probe makes oxidants such as dioxiranes appear to be more electrophilic than they actually are.     

Studies in heteroelement-based synthesis

An account of studies in our group over 30 years is presented, with highlights taken from events that began with our plans for medium ring synthesis, but were soon diverted to organophosphorus chemistry, and that eventually resulted in the investigation of sulfur ylide ring expansions, thiocarbonyl chemistry, azomethine ylides, organotin and organoboron methodology, and control of relative and absolute configuration.     

Versatile Reactions of Organoboron Polymers Prepared by Hydroboration Polymerization

Hydroboration polymerization of dienes and thexylborane produces organoboron polymers, which can be regarded as a polymer homolog of trialkylboranes. In other words, the organoboron polymers obtained can be expected to be a novel type of reactive polymer. The present paper describes versatile reactions of organoboron polymers prepared by hydroboration polymerization. For example, reactions with carbon monoxide or with KCN were followed by oxidative treatment to produce the corresponding poly(alcohol)s or poly(ketone)s, respectively. The organoboron polymers were also reacted with bromopyridyl anion or with furyl anion to form cyano- or hydroxyl-containing polymers via ring-opening of pyridine or furan, respectively. Reductive treatment of the organoboron polymer gave the corresponding polymer after reductive cleavage of carbon—boron bonds.     

Nickel‐Catalyzed Domino Heck‐Type Reactions Using Methyl Esters as Cross‐Coupling Electrophiles

While esters are frequently used as traditional electrophiles in substitution chemistry, their application in cross‐coupling chemistry is still in its infancy. This work demonstrates that methyl esters can be used as coupling electrophiles in Ni‐catalyzed Heck‐type reactions through the challenging cleavage of the C(acyl)?O bond under relatively mild reaction conditions at either 80 or 100 °C. With the σ‐Ni^II intermediate generated from the insertion of acyl Ni^II species into the tethered C=C bond, carbonyl‐retentive products were formed by domino Heck/Suzuki–Miyaura coupling and Heck/reduction pathways when organoboron and mild hydride nucleophiles are used.     

次氯酸钠对硫化橡胶粉表面的氧化改性研究

本文采用次氯酸钠对硫化橡胶粉进行表面氧化改性研究,通过X射线光电子能谱(XPS)、扫描电镜(SEM)、接触角测量对样品进行了表征和分析,并对其最佳工艺条件进行了探究。通过实验表明,氧化剂用量、反应温度及反应时间对胶粉的氧化反应都有影响。其最佳工艺条件的氧化剂用量为40%,反应温度为40℃左右,反应时间为3小时。