Unexpected Copper(II) Catalysis: Catalytic Amine Base Promoted β-Borylation of α,β-Unsaturated Carbonyl Compounds in Water

Location-Specific Microenvironment Modulation Around Single-Atom Metal Sites in Metal-Organic Frameworks for Boosting Catalysis

Despite coordination environment of catalytic metal sites has been recognized to be of great importance in single-atom catalysts (SACs), a significant challenge remains in the understanding how the location-specific microenvironment in the higher coordination sphere influences their catalysis. Herein, a series of Cu-based SACs, namely Cu1/UiO-66-X (X=-NO2, -H, and -NH2), are successfully constructed by anchoring single Cu atoms onto the Zr-oxo clusters of metal-organic frameworks (MOFs), i.e., UiO-66-X. The -X functional groups dangling on the MOF linkers could be regarded as location-specific remote microenvironment to regulate electronic properties of the single Cu atoms. Remarkably, they exhibit significant differences in the catalysis toward the hydroboration of alkynes. The activity follows the order of Cu1/UiO-66-NO2 > Cu1/UiO-66 > Cu1/UiO-66-NH2 under identical reaction conditions, where Cu1/UiO-66-NO2 showcases the phenylacetylene conversion of 92 %, ~3.5 times higher efficiency than that of Cu1/UiO-66-NH2. Experimental and calculation results jointly support that the Cu electronic structure is modulated by the location-specific microenvironment, thereby regulating the product desorption and promoting the catalysis.

Pd-Catalyzed Borylation in Water and Its Application to the Synthesis of Active Pharmaceutical Ingredient (API) Intermediates

An efficient catalytic borylation reaction of aryl bromides in water based on Pd catalysis under micellar conditions is presented. The peculiar combination of the proper Pd precursor with a Sphos ligand and a hindered lipophilic base ensures good yields in the synthesis of a wide range of boronic esters, even for heteroaryl derivatives with a good purity profile. The method is specifically developed for the in situ preparation of boronic esters that are directly converted into examples of relevant active pharmaceutical ingredient intermediates through cross-coupling reactions or via oxidation to phenols.

Cu(II)-Catalyzed Hydroboration Reactions of 1,1-Disubstituted α,β-Unsaturated Ketones, Esters, and Amides in Pure Water

Here, a Cu2(OH)2CO3-catalyzed hydroboration reaction of 1,1-disubstituted α,β-unsaturated compounds has been developed. The reaction was carried out using water as a solvent at room temperature except for N-monosubstituted α,β-unsaturated amides. This method is applicable to diverse 1,1-disubstituted α,β-unsaturated ketones, esters, and amides, showing excellent reactivity (up to 98% yield). Gram-scale experiments and functional group transformations further demonstrated the practicality of this method.

Copper Foam as Active Catalysts for the Borylation of α, β-Unsaturated Compounds

The use of simple, inexpensive, and efficient methods to construct carbon–boron and carbon–oxygen bonds has been a hot research topic in organic synthesis. We demonstrated that the desired β-boronic acid products can be obtained under mild conditions using copper foam as an efficient heterogeneous catalyst. The structure of copper foam before and after the reaction was investigated by polarized light microscopy (PM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and the results have shown that the structure of the catalyst copper foam remained unchanged before and after the reaction. The XPS test results showed that the Cu(0) content increased after the reaction, indicating that copper may be involved in the boron addition reaction. The specific optimization conditions were as follows: CH₃COCH₃ and H₂O were used as mixed solvents, 4-methoxychalcone was used as the raw material, 8 mg of catalyst was used and the reaction was carried out at room temperature and under air for 10 h. The yield of the product obtained was up to 92%, and the catalytic efficiency of the catalytic material remained largely unchanged after five cycles of use.

Development of Methods to the Synthesis of β-Boryl Acyls, Imines and Nitriles

Organoboron compounds are highly important and versatile synthetic intermediates for the preparation of a wide range of organic molecules. Organoboron compounds have drawn significant attention among organic chemists due to their Lewis acidic property, non-toxicity, and commercial availability. Over the last several decades, there has been a substantial development of new organoboron compounds, useful in organic synthesis. Among all other organoboron compounds, β-boryl carbonyl compounds are the important ones. The β-boryl compounds have appeared as promising intermediates for various synthetic transformations. The 1,4-conjugate addition of diboron reagents to carbon-carbon double bond in the presence of different transition-metal catalysts has been extensively reported by various research groups across the globe. This mini-review outlines the numerous racemic as well as asymmetric β-borylation methods developed to date.

Post-translational insertion of boron in proteins to probe and modulate function

Boron is absent in proteins, yet is a micronutrient. It possesses unique bonding that could expand biological function including modes of Lewis acidity not available to typical elements of life. Here we show that post-translational Cβ–Bγ bond formation provides mild, direct, site-selective access to the minimally sized residue boronoalanine (Bal) in proteins. Precise anchoring of boron within complex biomolecular systems allows dative bond-mediated, site-dependent protein Lewis acid–base-pairing (LABP) by Bal. Dynamic protein-LABP creates tunable inter- and intramolecular ligand–host interactions, while reactive protein-LABP reveals reactively accessible sites through migratory boron-to-oxygen Cβ–Oγ covalent bond formation. These modes of dative bonding can also generate de novo function, such as control of thermo- and proteolytic stability in a target protein, or observation of transient structural features via chemical exchange. These results indicate that controlled insertion of boron facilitates stability modulation, structure determination, de novo binding activities and redox-responsive ‘mutation’.

Post-translational site-selective formation of boronoalanine in proteins enables applications of boron for binding partner capture, footprinting of interactions with reactive oxygen species, proteolytic control and mapping of transient structures.

Creating High Regioselectivity by Electronic Metal-Support Interaction of a Single-Atomic-Site Catalyst

Ligands are the most commonly used means to control the regioselectivity of organic reactions. It is very important to develop new regioselective control methods for organic synthesis. In this study, we designed and synthesized a single-atomic-site catalyst (SAC), namely, Cu1-TiC, with strong electronic metal-support interaction (EMSI) effects by studying various reaction mechanisms. π cloud back-donation to the alkyne on the metal catalytic intermediate was enhanced during the reaction by using transient electron-rich characteristics. In this way, the reaction achieved highly linear-E-type regioselective conversion of electronically unbiased alkynes and completely avoided the formation of branched isomers (ln:br >100:1, TON up to 612, 3 times higher than previously recorded). The structural elements of the SACs were designed following the requirements of the synthesis mechanism. Every element in the catalyst played an important role in the synthesis mechanism. This demonstrated that the EMSI, which is normally thought to be responsible for the improvement in catalytic efficiency and durability in heterogeneous catalysis, now first shows exciting potential for regulating the regioselectivity in homogeneous catalysis.

α,β-Enone Borylation by Bis(Pinacolato)Diboron Catalyzed by Cu3(BTC)2 Using Cesium Carbonate as a Base

Cu₃(BTC)₂ (BTC: 1,3,5-benzenetricarboxylate) as a heterogeneous catalyst in the presence of cesium carbonate as a base is reported for the borylation of α,β-conjugated enones by bis(pinacolato)diboron (B₂pin₂). According to the hot-filtration test, Cu₃(BTC)₂ is acting as a heterogeneous catalyst. Further, Cu₃(BTC)₂ exhibits a wide substrate scope and can be reused in consecutive runs, maintaining a crystal structure as evidenced by powder X-ray diffraction (XRD). A suitable mechanism is also proposed for this transformation using Cu₃(BTC)₂ as catalyst.

Rapid and Selective Chemical Editing of Ribosomally Synthesized and Post-Translationally Modified Peptides (RiPPs) via CuII -Catalyzed β-Borylation of Dehydroamino Acids

We report the fast and selective chemical editing of ribosomally synthesized and post-translationally modified peptides (RiPPs) by β-borylation of dehydroalanine (Dha) residues. The thiopeptide thiostrepton was modified efficiently using CuII -catalysis under mild conditions and 1D/2D NMR of the purified product showed site-selective borylation of the terminal Dha residues. Using similar conditions, the thiopeptide nosiheptide, lanthipeptide nisin Z, and protein SUMO_G98Dha were also modified efficiently. Borylated thiostrepton showed an up to 84-fold increase in water solubility, and minimum inhibitory concentration (MIC) assays showed that antimicrobial activity was maintained in thiostrepton and nosiheptide. The introduced boronic-acid functionalities were shown to be valuable handles for chemical mutagenesis and in a reversible click reaction with triols for the pH-controlled labeling of RiPPs.

Copper(ii)-catalyzed protoboration of allenes in aqueous media and open air

A copper(ii)-catalyzed internal protoboration of monosubstituted allenes efficiently occurs in water at room temperature and open air to generate 1,1-disubstituted vinyl boronic acid derivatives.

Cu-tetracatechol metallopolymer catalyst for three component click reactions and β-borylation of α,β-unsaturated carbonyl compounds

Phenol-metal coordination polymers are used in applications such as catalysis, sensing and separation science. In addition, combining eco-friendly conditions with economical and handling advantages of the polymeric catalyst is of interest to the community. Here, we report a simple one pot synthesis of a tetracatechol based ligand and its coordination polymer with copper ions. The Cu polymer showed electrochemical potential with a band gap of 1.01 eV. The BET surface area of the metallopolymer was 91.19 m2 g-1 with 0.14 cm3 g-1 pore volume. The polymer catalyst was used in a one pot three component click reaction and in the borylation of unsaturated carbonyl compounds with a maximum 99% conversion in water and good turnover efficiency even after 4 repetitive catalysis cycles. The polymer catalyst offers several advantages such as high activity, easy handling, scalability, recyclability and cost effectiveness.

β-Borylation of conjugated carbonyl compounds with silylborane or bis(pinacolato)diboron catalyzed by Au nanoparticles

β-Borylation occurs in the Au/TiO₂-catalysed reaction between the silylborane Me₂PhSiBpin and conjugated carbonyl compounds, in contrast to the so far known analogous reaction catalysed by other metals, where β-silylation occurs instead.

Route to Air and Moisture Stable β-Difluoroboryl Acrylamides

A method for the preparation of air stable difluoroboryl acrylamides is reported. In contrast to the ubiquitous organotrifluoroborate salts, difluoroboryl acrylamides are relatively nonpolar and are readily purified by silica chromatography. Difluoroboryl acrylamides serve as efficient substrates in cross-coupling reactions to afford the corresponding trisubstituted acrylamides in good to excellent yields. The utility of the difluoroboryl group in various chemical transformations is presented.

Ru-Catalyzed Chemo- and Enantioselective Hydrogenation of β-Diketones Assisted by the Neighboring Heteroatoms

A highly chemo- and enantioselective hydrogenation of β-diketones was achieved by using [Ru(benzene)(S)-SunPhosCl]Cl for consistency in THF. The neighboring heteroatoms played important roles in guaranteeing the reactivity and controlling the chemoselectivity. These results suggested a potential approach for the clean and facile synthesis of functionalized chiral β-hydroxy ketones, which could otherwise be prepared through much less step-economic transformations.

2-Methyl-substituted monotetrazoles in copper(ii) perchlorate complexes: manipulating coordination chemistry and derived energetic properties

Several new energetic coordination compounds (ECC) have been prepared using two 2-methyl-substituted tetrazoles. By simply changing the reaction conditions, the coordination sphere of the metal center can be manipulated in order to obtain different complexes with varying energetic properties.

Copper-boryl mediated organic synthesis

Organoboron compounds are valuable synthetic intermediates that find application in a diverse variety of processes including both C-X and C-C bond-forming transformations. This has been achieved by using a variety of boron derivatives. Of these, boronate esters are probably the most versatile and, reflecting this, methods for the generation of boronate esters are of considerable current interest. Given the mild reaction conditions, good functional group tolerance, and low cost of the metal catalyst, the use of copper-boryl reagents is particularly attractive. In this review, methodologies in copper-boryl chemistry are discussed and the many different transformations possible are surveyed.

Borylation of α,β-Unsaturated Acceptors by Chitosan Composite Film Supported Copper Nanoparticles

We describe here the preparation of copper nanoparticles stabilized on a chitosan/poly (vinyl alcohol) composite film. This material could catalyze the borylation of α,β-unsaturated acceptors in aqueous media under mild conditions. The corresponding organoboron compounds as well as their converted β-hydroxyl products were all obtained in good to excellent yields. It is noteworthy that this catalyst of copper nanoparticles can be easily recycled eight times and remained catalytically reactive. This newly developed methodology provides an efficient and sustainable pathway for the synthesis of organoboron compounds and application of copper nanoparticles.

Recent advances in the synthesis of functionalised monofluorinated compounds

Over the past few years, we have tackled the synthesis of interesting monofluorinated organic molecules, such as: dihydronaphthalene derivatives, β-fluoro sulfones and related carbonyl compounds, fluorohydrins and allylic alcohols.

Substrate-Assisted, Transition-Metal-Free Diboration of Alkynamides with Mixed Diboron: Regio- and Stereoselective Access to trans-1,2-Vinyldiboronates

A substrate-assisted diboration of alkynamides using the unsymmetrical pinacolato-1,8-diaminonaphthalenato diboron (pinBBdan) is described. The transition-metal-free reaction proceeds in a regio- and stereoselective fashion to exclusively afford trans-vinyldiboronates in good to excellent yields. Notably, Bdan and Bpin are installed on the α- and β-carbon atoms, respectively.

Direct α-Arylation/Heteroarylation of 2-Trifluoroboratochromanones via Photoredox/Nickel Dual Catalysis

Utilizing photoredox/nickel dual catalysis, diverse flavanones have been synthesized by coupling novel 2-trifluoroboratochromanone building blocks with aryl and heteroaryl bromide partners. The newly reported trifluoroboratochromanones can be easily accessed from the corresponding chromones on multigram scale. This represents a general route for accessing natural and unnatural flavanones that were previously formed through a synthetically more restrictive ring closure route from chalcone precursors.

Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse

Although known for over 90 years, only in the past two decades has the chemistry of diboron(4) compounds been extensively explored. Many interesting structural features and reaction patterns have emerged, and more importantly, these compounds now feature prominently in both metal-catalyzed and metal-free methodologies for the formation of B-C bonds and other processes.

Efficient metal-free photochemical borylation of aryl halides under batch and continuous-flow conditions

A rapid, chemoselective and metal-free C-B bond-forming reaction of aryl iodides and bromides in aqueous solution at low temperatures was discovered. This reaction is amenable to batch and continuous-flow conditions and shows exceptional functional group tolerance and broad substrate scope regarding both the aryl halide and the borylating reagent. Initial mechanistic experiments indicated a photolytically generated aryl radical as the key intermediate.

Copper-catalyzed hydroboration of propargyl-functionalized alkynes in water

The Cu-catalyzed hydroboration of alkynes in operationally simple and environmentally friendly conditions is reported.

Chemoselective catalytic reduction of conjugated α,β-unsaturated ketones to saturated ketones via a hydroboration/protodeboronation strategy

A novel copper-catalyzed chemoselective reduction of a carbon–carbon double or triple bond to a carbon–carbon single bond on α,β-unsaturated ketones is developed, this reaction proceeds under hydrogen gas or stoichiometric metal hydride free conditions.

Crystal structure of catena-poly[[chlorido-(4,4'-dimethyl-2,2'-bi-pyridine-κ(2) N,N')copper(II)]-μ-chlorido]

The title compound, [CuCl2(C12H12N2)] n , was obtained via a DMSO-mediated dehydration of Cu(4,4'-dimethyl-2,2'-bi-pyridine)-copper(II)·0.25H2O. The central Cu(II) atom is coordinated in a distorted trigonal-bipyramidal geometry by two N atoms of a chelating 4,4'-dimethyl-2,2'-bi-pyridine ligand [average Cu-N = 2.03 (3) Å] and three Cl atoms, one terminal with a short Cu-Cl bond of 2.2506 (10) Å, and two symmetry-equivalent and bridging bonds. The bridging Cl atom links the Cu(II) ions into chains parallel to [001] via one medium and one long Cu-Cl bond [2.3320 (10) and 2.5623 (9) Å]. The structure displays both inter- and intra-molecular C-H⋯Cl hydrogen bonding.

A Cu(ii)-based strategy for catalytic enantioselective β-borylation of α,β-unsaturated acceptors

The unique nature and readily availability of Cu(v) species underscores the value of the Cu(v)-based catalyst over an array of well-documented Cu(i)-based catalysts.