Borylation Reactions Research Articles

Coupling of thiols and aromatic halides promoted by diboron derived super electron donors.

We have proven that pyridine-boryl complexes can be used as superelectron donors to promote the coupling of thiols and aromatic halides through a SRN1 mechanism. The reaction is efficient for a broad substrate scope, tolerating heterocycles including pyridines, enolizable or reducible functional groups. The method has been applied to intermediates in drug synthesis as well as interesting functionalized polythioethers through a controlled and consecutive intramolecular electron transfer process.

Pyrimidine-directed metal-free C-H borylation of 2-pyrimidylanilines: a useful process for tetra-coordinated triarylborane synthesis.

Convenient, easily handled, laboratory friendly, robust approaches to afford synthetically important organoboron compounds are currently of great interest to researchers. Among the various available strategies, a metal-free approach would be overwhelmingly accepted, since the target boron compounds can be prepared in a metal-free state. We herein present a detailed study of the metal-free directed ortho-C–H borylation of 2-pyrimidylaniline derivatives. The approach allowed us to synthesize various boronates, which are synthetically important compounds and various four-coordinated triarylborane derivatives, which could be useful in materials science as well as Lewis-acid catalysts. This metal-free directed C–H borylation reaction proceeds smoothly without any interference by external impurities, such as inorganic salts, reactive functionalities, heterocycles and even transition metal precursors, which further enhance its importance.

Selective electrocatalytic hydroboration of aryl alkenes

A CH3CN-involved electrochemical mono- or di-functional borylation reaction with alkenes and HBpin as substrates was reported. Functional group transformation and gram-scale synthesis demonstrated the utility of this method and showed great potential application.

Synthetic Chemistry with Lewis Acidity‐Diminished B(aam) and B(dan) Groups: Borylation Reactions and Direct Cross‐Couplings

AbstractThis review describes recent advances in the synthesis of anthranilamide/1,8‐diaminonaphthalene‐substituted organoboron compounds with diminished boron Lewis acidity via catalytic B(aam)‐ and B(dan)‐installing borylation reactions, which have attracted growing attention especially in the last five years owing to their unique reactivity, regioselectivity, and the outstanding stability toward air and moisture of organoboron compounds obtained therefrom. Direct Suzuki–Miyaura cross‐couplings with R–B(aam)/B(dan), which were believed to be wholly unreactive until recently, are also discussed.magnified image

Development of One-Shot/One-Pot Borylation Reactions toward Organoboron-Based Materials

AbstractThis account highlights the development of efficient borylation reactions of arenes toward organoboron-based materials. Upon the introduction of boron substituents, an intramolecular tandem bora-Friedel–Crafts reaction (tandem electrophilic C–H borylation of arenes) takes place with the appropriate choices of boron source, Lewis acid, Brønsted base, and reaction temperature to construct polycyclic frameworks with ring-junction boron atoms in a one-pot manner. Notably, electron-rich arenes, such as triarylamines, undergo one-shot multiple (up to quadruple) borylations with boron trihalides through successive inter- and intramolecular processes. The borylated compounds exhibit attractive optoelectronic properties and substantial stabilities in practical applications. These reactions are efficient, facile, scalable, and free from precious reagents, and will thus pave the way for the development of next-generation optoelectronic materials.

Photoinduced Borylation Reactions: An Overview

AbstractThe photochemical reactions perform a progressively important role in the field of green chemistry and organic synthesis from the last decades. It has always been considered as eco‐friendly, inexpensive, most abundant and endlessly renewable energy source. The organoboronic acids and esters occupy a central position in the field of chemistry so the development of novel methodology for the preparation of organoboron compounds is essential. In recent years, visible light‐induced photoredox catalysis has created a more influence on the preparation of different organoboron compounds using novel synthetic methodologies with very mild and eco‐friendly conditions. In this review, we have provided a brief overview of preparation of organoboronic acids or esters from aliphatic, aromatic C−H/C−X and other functional groups by photoredox methodology.

Improvement in the Palladium-Catalyzed Miyaura Borylation Reaction by Optimization of the Base: Scope and Mechanistic Study.

Aryl boronic acids and esters are important building blocks in API synthesis. The palladium-catalyzed Suzuki-Miyaura borylation is the most common method for their preparation. This paper describes an improvement of the current reaction conditions. By using lipophilic bases such as potassium 2-ethyl hexanoate, the borylation reaction could be achieved at 35 °C in less than 2 h with very low palladium loading (0.5 mol %). A preliminary mechanistic study shows a hitherto unrecognized inhibitory effect by the carboxylate anion on the catalytic cycle, whereas 2-ethyl hexanoate minimizes this inhibitory effect. This improved methodology enables borylation of a wide range of substrates under mild conditions.

Alkane borylation reaction kicks metals to the curb

Alkane borylation reaction kicks metals to the curb

Hybrid POCZP Aryl Pincer Metal Complexes and their Catalytic Applications

The use of XCX‐aryl pincer metal complexes as catalysts started immediately after their discovery in 1976. Nowadays pincer metal complexes are commonly used as a new platform for the development and improvement of known and novel catalytic reactions. More recently, pincer metal complexes with hybrid pincer backbones of the type POCZP (Z = CH2, NH or S) have attracted much attention because of their facile preparation and outstanding catalytic performances. For instance, these complexes have been successfully used in cross‐coupling, transfer hydrogenation, and borylation reactions. In many cases, showing enhanced catalytic activities compared with POCOP‐ or PZCZP‐aryl pincer metal analogues. Hence, in this Minireview we summarize the available synthetic routes to produce POCZP aryl pincer ligands and their metal complexes as well as their applications as catalysts in different organic transformations.

Visible-Light-Induced Ni-Catalyzed Radical Borylation of Chloroarenes.

A highly selective and general photoinduced C-Cl borylation protocol that employs [Ni(IMes)2] (IMes = 1,3-dimesitylimidazoline-2-ylidene) for the radical borylation of chloroarenes is reported. This photoinduced system operates with visible light (400 nm) and achieves borylation of a wide range of chloroarenes with B2pin2 at room temperature in excellent yields and with high selectivity, thereby demonstrating its broad utility and functional group tolerance. Mechanistic investigations suggest that the borylation reactions proceed via a radical process. EPR studies demonstrate that [Ni(IMes)2] undergoes very fast chlorine atom abstraction from aryl chlorides to give [NiI(IMes)2Cl] and aryl radicals. Control experiments indicate that light promotes the reaction of [NiI(IMes)2Cl] with aryl chlorides generating additional aryl radicals and [NiII(IMes)2Cl2]. The aryl radicals react with an anionic sp2-sp3 diborane [B2pin2(OMe)]- formed from B2pin2 and KOMe to yield the corresponding borylation product and the [Bpin(OMe)]•- radical anion, which reduces [NiII(IMes)2Cl2] under irradiation to regenerate [NiI(IMes)2Cl] and [Ni(IMes)2] for the next catalytic cycle.

Phosphine-Directed sp3 C-H, C-O, and C-N Borylation.

Benzylic C-H borylation reactions are limited, requiring new approaches to exploit their reactivity for efficient selective functionalization. The recent development of phosphine-directed C-H borylation of arenes has now been extended to benzylic substrates, providing high yield of the mono- and geminal bis-borylation products. Attempts to borylate the C-H bond α to a benzylic ether or amine resulted in C-O and C-N borylation, followed by C-H borylation to provide geminal bis-borylated products.

Synthesis of Biquinolines via a Pd‐Catalyzed Borylation Reaction

AbstractSynthesis of biquinolines starting from easily available haloquinolines via a Pd‐catalyzed borylation reaction in the presence of inexpensive bis(pinacolato)diboron is described. The reaction involves Pd(dppf)Cl2 ⋅ CH2Cl2‐catalyzed cross‐coupling of haloquinolines with bis(pinacolato)diboron to afford in situ generated heteroarylboronates. The intermediate heteroarylboronates immediately undergoes homocoupling to afford biquinolines in good to excellent yields in short reaction time. The scope of the reaction was demonstrated by its successful extension to structurally related N‐heterocycles.

Selective Vicinal Diiodination of Polycyclic Aromatic Hydrocarbons

Vicinally diiodinated polycyclic aromatic hydrocarbons (I2‐PAHs) are accessible from the corresponding diborylated B2‐PAHs through boron/iodine exchange. The B2‐PAHs have been prepared via twofold electrophilic borylation reactions templated by a vicinally disilylated benzene. Our protocol is applicable to fluorenes, acenes, annulated acenes, oligoaryls, and even [5]helicene. Using B2‐naphthalene as the example, we have shown that the reaction scope can, in principle, be expanded to include the synthesis of vicinally dibrominated and dihydroxylated PAHs. The usefulness of the building blocks provided by our method in the field of optoelectronic materials was demonstrated by the successful conversion of I2‐fluoranthene to the analogous doubly alkynylated fluoranthene emitter.

Boron Recycling in the Metal-Free Transfer C–H Borylation of Terminal Alkynes and Heteroarenes

Transfer C–H borylation is an isodesmic approach to the borylation reaction using B–C-containing molecules as boron sources. In this work, we report that 2-mercaptothiazole and other analogues are ...

Transition-Metal-Free Borylation of Aryl Bromide Using a Simple Diboron Source.

In this study, we developed a simple transition-metal-free borylation reaction of aryl bromides. Bis-boronic acid (BBA), was used, and the borylation reaction was performed using a simple procedure at a mild temperature. Under mild conditions, aryl bromides were converted to arylboronic acids directly without any deprotection steps and purified by conversion to trifluoroborate salts. The functional group tolerance was considerably high. The mechanism study suggested that this borylation reaction proceeds via a radical pathway.

Synthesis and Properties of Perylene-Bridge-Anchor Chromophoric Compounds.

The quest to control chromophore/semiconductor properties to enable new technologies in energy and information science requires detailed understanding of charge carrier dynamics at the atomistic level, which can often be attained through the use of model systems. Perylene-bridge-anchor compounds are successful models for studying fundamental charge transfer processes on TiO2, which remains among the most commonly investigated and technologically important interfaces, mostly because of perylene's advantageous electronic and optical properties. Nonetheless, the ability to fully exploit synthetically the substitution pattern of perylene with linker (= bridge-anchor) units remains little explored. Here we developed 2,5-di-tert-butylperylene (DtBuPe)-bridge-anchor compounds with t-Bu group substituents to prevent π-stacking and one or two linker units in both the peri and ortho positions, by employing a combination of Friedel-Crafts alkylations, bromination, iridium-catalyzed borylation, and palladium-catalyzed cross-coupling reactions. Photophysical characterization and computational analysis by density functional theory (DFT) and time-dependent DFT (TD-DFT) were carried out on four DtBuPe acrylic acid derivatives with a single or a double linker in peri (12b), ortho (15b), peri,peri (18b), and ortho,ortho (21b). The energies of the unoccupied orbitals {LUMO, LUMO + 1, LUMO + 2} are strongly affected by the presence of a π-conjugated linker, resulting in a stabilization of these states and a red shift of their absorption and emission spectra, as well as the loss of vibronic structure in the spectrum of the peri,peri compound, consistent with the strong bonding character of this substitution pattern.

Convenient synthesis of tetracoordinated organoboron compounds via C[sbnd]H borylation of aryl-N-heteroaromatics with TfOBnBu2

An efficient method to synthesize tetracoordinated N,C-chelate organoboron compounds is described. The metal-free CH borylation reactions of 2-arylpyridine derivatives with TfOBnBu2 proceeds smoothly to yield 2-(2-dibutylborylaryl)pyridine derivatives in satisfactory to excellent yields. Different substituents, such as methyl, methoxy, fluoro, chloro, bromo, and carbonyl, on 2-arylpyridine are tolerated under optimal reaction conditions.

Transformations of Aryl Ketones via Ligand‐Promoted C−C Bond Activation

AbstractThe coupling of aromatic electrophiles (aryl halides, aryl ethers, aryl acids, aryl nitriles etc.) with nucleophiles is a core methodology for the synthesis of aryl compounds. Transformations of aryl ketones in an analogous manner via carbon–carbon bond activation could greatly expand the toolbox for the synthesis of aryl compounds due to the abundance of aryl ketones. An exploratory study of this approach is typically based on carbon–carbon cleavage triggered by ring‐strain release and chelation assistance, and the products are also limited to a specific structural motif. Here we report a ligand‐promoted β‐carbon elimination strategy to activate the carbon–carbon bonds, which results in a range of transformations of aryl ketones, leading to useful aryl borates, and also to biaryls, aryl nitriles, and aryl alkenes. The use of a pyridine‐oxazoline ligand is crucial for this catalytic transformation. A gram‐scale borylation reaction of an aryl ketone via a simple one‐pot operation is reported. The potential utility of this strategy is also demonstrated by the late‐stage diversification of drug molecules probenecid, adapalene, and desoxyestrone, the fragrance tonalid as well as the natural product apocynin.

Transformations of Aryl Ketones via Ligand-Promoted C-C Bond Activation.

The coupling of aromatic electrophiles (aryl halides, aryl ethers, aryl acids, aryl nitriles etc.) with nucleophiles is a core methodology for the synthesis of aryl compounds. Transformations of aryl ketones in an analogous manner via carbon-carbon bond activation could greatly expand the toolbox for the synthesis of aryl compounds due to the abundance of aryl ketones. An exploratory study of this approach is typically based on carbon-carbon cleavage triggered by ring-strain release and chelation assistance, and the products are also limited to a specific structural motif. Here we report a ligand-promoted β-carbon elimination strategy to activate the carbon-carbon bonds, which results in a range of transformations of aryl ketones, leading to useful aryl borates, and also to biaryls, aryl nitriles, and aryl alkenes. The use of a pyridine-oxazoline ligand is crucial for this catalytic transformation. A gram-scale borylation reaction of an aryl ketone via a simple one-pot operation is reported. The potential utility of this strategy is also demonstrated by the late-stage diversification of drug molecules probenecid, adapalene, and desoxyestrone, the fragrance tonalid as well as the natural product apocynin.

Miyaura Borylation Reaction

Key words Miyaura borylation - cross-coupling - palladium catalysis - arylboronic esters