Organoboronic Acids Research Articles

Diastereo-, Enantio-, and Z-Selective α,δ-Difunctionalization of Electron-Deficient Dienes Initiated by Rh-Catalyzed Conjugate Addition.

Metal-catalyzed enantioselective conjugate additions are highly reliable methods for stereoselective synthesis; however, multicomponent reactions that are initiated by conjugate arylation of acyclic π-systems are rare. These reactions generally proceed with poor diastereoselectivity while requiring basic, moisture sensitive organometallic nucleophiles. Here, we show that Rh-catalysts supported by a tetrafluorobenzobarrelene ligand (Ph-tfb) enable the enantio-, diastereo-, and Z-selective α,δ-difunctionalization of electron-deficient 1,3-dienes with organoboronic acid nucleophiles and aldehyde electrophiles to generate Z-homoallylic alcohols with three stereocenters. The reaction accommodates diene substrates activated by ester, amide, ketone, or aromatic groups and can be used to couple aryl, alkenyl, or alkyl aldehydes. Diastereoselective functionalization of the Z-olefin unit in the addition products allows for the generation of compounds with five stereocenters in high dr and ee. Mechanistic studies suggest aldehyde allylrhodation is the rate-determining step, and unlike reactions of analogous Rh-enolates, the Rh-allyl species generated by δ-arylation undergoes aldehyde trapping rather than protonolysis, even when water is present as a cosolvent. These findings should have broader implications in the use of privileged metal-catalyzed conjugate addition reactions as entry points toward the preparation of acyclic molecules containing nonadjacent stereocenters.

Generation of Functionalized Alkyl Radicals via the Direct Photoexcitation of 2,2'-(Pyridine-2,6-diyl)diphenol-Based Borates.

A new type of alkylborate was developed for the purpose of generating radicals via direct photoexcitation. These borates were prepared using 2,2'-(pyridine-2,6-diyl)diphenol as a tridentate ligand together with organoboronic acids or potassium trifluoroborates. The ready availability of organoboron compounds is a significant advantage of this direct photoexcitation protocol. The excited states of these borates can also serve as strong reductants, enabling various transformations.

High Proton-Conductivity in Covalently Linked Polyoxometalate-Organoboronic Acid-Polymers.

The controlled bottom‐up design of polymers with metal oxide backbones is a grand challenge in materials design, as it could give unique control over the resulting chemical properties. Herein, we report a 1D‐organo‐functionalized polyoxometalate polymer featuring a purely inorganic backbone. The polymer is self‐assembled from two types of monomers, inorganic Wells–Dawson‐type polyoxometalates, and aromatic organo‐boronates. Their covalent linkage results in 1D polymer strands, which combine an inorganic oxide backbone (based on B−O and Nb−O linkages) with functional organic side‐chains. The polymer shows high bulk proton conductivity of up to 1.59×10−1 S cm−1 at 90 °C and 98 % relative humidity. This synthetic approach could lead to a new class of organic–inorganic polymers where function can be designed by controlled tuning of the monomer units.

A Dichotomy in Cross-Coupling Site Selectivity in a Dihalogenated Heteroarene: Influence of Mononuclear Pd, Pd Clusters, and Pd Nanoparticles-the Case for Exploiting Pd Catalyst Speciation.

Site-selective dihalogenated heteroarene cross-coupling with organometallic reagents usually occurs at the halogen proximal to the heteroatom, enabled by intrinsic relative electrophilicity, particularly in strongly polarized systems. An archetypical example is the Suzuki–Miyaura cross-coupling (SMCC) of 2,4-dibromopyridine with organoboron species, which typically exhibit C2-arylation site-selectivity using mononuclear Pd (pre)catalysts. Given that Pd speciation, particularly aggregation, is known to lead to the formation of catalytically competent multinuclear Pdn species, the influence of these species on cross-coupling site-selectivity remains largely unknown. Herein, we disclose that multinuclear Pd species, in the form of Pd3-type clusters and nanoparticles, switch arylation site-selectivity from C2 to C4, in 2,4-dibromopyridine cross-couplings with both organoboronic acids (SMCC reactions) and Grignard reagents (Kumada-type reactions). The Pd/ligand ratio and the presence of suitable stabilizing salts were found to be critically important in switching the site-selectivity. More generally, this study provides experimental evidence that aggregated Pd catalyst species not only are catalytically competent but also alter reaction outcomes through changes in product selectivity.

Transition‐Metal‐Free DMAP‐Mediated Aromatic Esterification of Amides with Organoboronic Acids

AbstractA new, transition‐metal‐free, effective method for aromatic esterification of amides with organoboronic acids has been developed. A wide range of benzoate derivatives were obtained with yields ranging from moderate to good. The catalytic reaction shows a broad substrate scope and excellent functional group tolerance. Conceptually, DMAP mediates the reaction and is crucial for this transformation.

Sterically Protected and Conformation-Restricted BOBHY Dyes with Bright Near-Infrared Fluorescence: N2O-type Expanded BOPHY Dyes Derived from Boronic Acids.

A new family of N2O-type hydrazine-containing bipyrrole boron complexes has been developed via a one-pot condensation of formylisoindole, hydrazine, and various organoboronic acids. Because of the conformation-restricted coplanar structure and the axial-substituted aryl groups, these novel dyes show deep-red absorption, bright near-infrared (NIR) fluorescence in both solution and solid states, and good solubility in organic solvents. The derivative with pyridinium ions also has been synthesized as an NIR mitochondrially targetable fluorescent probe.

The Mechanism and Origin of Enantioselectivity in the Rhodium-Catalyzed Asymmetric Ring-Opening Reactions of Oxabicyclic Alkenes with Organoboronic Acids: A DFT Investigation

The mechanism and origins of enantio- and stereoselectivity in the asymmetric ring-opening (ARO) reactions of oxabicyclic alkenes with organoboronic acids catalyzed by rhodium/Josiphos has been examined at the B3LYP/defTZVP level of theory. The mechanism consists of four steps including transmetalation, carborhodation, β-oxygen elimination, and hydrolysis. Energetic discrimination in the chirality-imparting step arises from attractive C–H−π interactions between the transmetalated aryl group and the Josiphos ligand, as well as steric clashes between the Josiphos ligand and the oxabicyclic alkene. Computational results indicate that the rate-determining step is involved in the hydrolysis of the rhodium(I) alkoxide from the ring-opened intermediate. In the overall catalytic cycle, the greatest free energy barrier is 23.4 kcal/mol, which supports that the Rh-catalyzed ARO reactions take place at mild reaction conditions, which is consistent with experimental observations.

Synthetic Approaches to N‐Methoxy‐N‐methylamides

N‐Methoxy‐N‐methylamides were prepared by the acylation of acid halides, acyl cyanides, esters, lactones, activated amides, and mesyl carboxylates with N,O‐dimethylhydroxylamine hydrochloride. The reaction of carboxylic acids with alkyl chloroformates, phosphonate reagents, or coupling agents afforded the activated esters, which were converted to N‐methoxy‐N‐methylamides by (CH3O)NHCH3. N‐Methoxy‐N‐methylamides were also prepared by the oxidative amidation of benzyl alcohols and palladium‐catalyzed aminocarbonylation of organoboronic acids or aryl halides with (CH3O)NHCH3 under CO equivalents. Furthermore, N‐methoxy‐N‐methylamides were produced by the selective substitution of N,O‐dimethylcarbamoylation agents with organometallic reagents.

Catalyst-free and eco-friendly synthesis of masked haloarylboronic acids R (alkyl or aryl)-B(dan) on water

An environment-friendly methodology for the synthesis of R (alkyl or aryl)-B(dan) on water is described. 1,8-diamino naphthalene(danH 2 ) was reacted with different types of organoboronic acids to furnish the products in moderate to excellent yields. A multi-gram scale reaction is also performed to ensure the scalability of the reaction. • The greenest protocol for the synthesis of Masked Haloarylboronic Acids R (Alkyl or Aryl)-B(dan). • A catalyst-free transformation under “on water” conditions. • Several examples with high-excellent yields. • Experiments to verify the theory of “on water” reaction.

Palladium catalyzed desulfurative coupling of allyl sulfides with organoboronic acids

A palladium catalyzed desulfurative coupling of allylthioethers with organoboronic acids under mild reaction conditions is described.

Mn(iii)-mediated cascade cyclization of 1-(azidomethyl)-2-isocyanoarenes with organoboronic acids: construction of quinazoline derivatives

A novel and efficient Mn(iii)-mediated oxidative radical cascade reaction of 1-(azidomethyl)-2-isocyanoarenes with organoboronic acids is reported.

Synthesis of ortho-arylated and alkenylated benzamides by palladium-catalyzed denitrogenative cross-coupling reactions of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids

An efficient palladium-catalyzed denitrogenative cross-coupling reaction of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids is described. The reaction affords various ortho-aryl and alkenylated benzamides in good to high yields.

Hydroxyl group-directed, tartaric acid-catalyzed synthesis of meta-functionalized aryl ethers and phenols through domino conjugate addition/aromatization of para-quinols

A tartaric acid-catalyzed three-component reaction of para-quinols, organoboronic acids, and alcohols affords meta-alkenylated aryl alkyl ether in good yields. In the absence of alcohols, meta-functionalized phenols could be obtained selectively.

Synthesis and optical properties of N→Ga coordinated gallium boroxines.

Reactions of the N,C,N-chelated organogallium amide LGa(NEt2)2 (1), where L is {2,6-(Me2NCH2)2C6H3}-, with organoboronic acids RB(OH)2 yielded molecular gallium boroxines LGa(O3B2R2) (2: R = OH, 3: R = Ph, 4: R = 4-MeO-C6H4, 5: R = 4-CHO-C6H4, 6: R = Fc), neutral analogues of gallaborates. The molecular structures revealed the presence of a six-membered central GaB2O3 ring. The film forming properties of 5 allowed the deposition of transparent thin films by a spin coating method. The thicknesses, refractive index, energy of the optical gap (Eoptg), activation energy of surface electrical conductivity (Esa) and pre-exponential factor (σ0) of the thin layers of 5 were measured and they are close to those found for related oxygen glass. Finally, GBO 5 was also used as an additive to printing ink and a thin film of 5 was prepared by the gravure printing technique.

Catalytic Synthesis of Potassium Acyltrifluoroborates (KATs) from Boronic Acids and the Thioimidate KAT Transfer Reagent.

We report the synthesis of potassium acyltrifluoroborates (KATs) by a palladium-catalyzed cross-coupling of boronic acids and the thioimidate KAT transfer reagent. The combination of widely available aryl- and vinylboronic acids with commercially available thioimidate 1 using catalytic PdII and a CuII additive enables the preparation of KATs in high yields and with good functional group tolerance. This formal insertion of CO into organoboronic acids can also be applied to boronic acid pinacol esters and potassium organotrifluoroborates using a slightly modified procedure. The cross-coupling can be telescoped into the one-pot synthesis of amides and α-aminotrifluoroborates by exploiting the unique chemistry of KATs and their trifluoroborate iminium (TIM) derivatives.

Catalyst‐Free Four‐Component Polymerization of Propiolic Acids, Benzylamines, Organoboronic Acids, and Formaldehyde toward Functional Poly(propargylamine)s

Multicomponent polymerizations (MCPs) are a group of fascinating polymer synthesis approaches that are developed rapidly in the recent decade. As a popular alkyne-based MCP, the A3 -polycouplings of alkynes, aldehydes, and amines are developed for the synthesis of poly(propargylamine)s under the catalysis of metal catalysts. In this work, through the design of carboxylic acid group-activated alkyne monomers, a catalyst-free, four-component polymerization of propiolic acids, benzylamines, organoboronic acids, and formaldehyde is reported under mild condition at 45°C in dichloroethane. This four-component polymerization is applicable to different monomer structures, which can afford seven poly(propargylamine)s with up to 94% yields and molecular weights of up to 13 900gmol-1 . Moreover, the poly(propargylamine)s demonstrate good solubility and processibility, high thermal stability and light refractivity, unique photophysical property, and so on. The simple monomers, mild condition, low cost, high efficiency, and procedure simplicity of this catalyst-free four-component polymerization demonstrates an elegant example of functional polymer synthesis.

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.

Nickel‐ and Palladium‐Catalyzed Cross‐Coupling Reactions of Organostibines with Organoboronic Acids

AbstractA strategy for the formation of antimony‐carbon bond was developed by nickel‐catalyzed cross‐coupling of halostibines. This method has been applied to the synthesis of various triaryl‐ and diarylalkylstibines from the corresponding cyclic and acyclic halostibines. This protocol showed a wide substrate scope (72 examples) and was compatible to a wide range of functional groups such as aldehyde, ketone, alkene, alkyne, haloarenes (F, Cl, Br, I), and heteroarenes. A successful synthesis of arylated stibine 3 a in a scale of 34.77 g demonstrates high synthetic potential of this transformation. The formed stibines (R3Sb) were then used for the palladium‐catalyzed carbon–carbon bond forming reaction with aryl boronic acids [R−B(OH)2], giving biaryls with high selectivity, even the structures of two organomoieties (R and R′) are very similar. Plausible catalytic pathways were proposed based on control experiments.

Nickel- and Palladium-Catalyzed Cross-Coupling Reactions of Organostibines with Organoboronic Acids.

A strategy for the formation of antimony-carbon bond was developed by nickel-catalyzed cross-coupling of halostibines. This method has been applied to the synthesis of various triaryl- and diarylalkylstibines from the corresponding cyclic and acyclic halostibines. This protocol showed a wide substrate scope (72 examples) and was compatible to a wide range of functional groups such as aldehyde, ketone, alkene, alkyne, haloarenes (F, Cl, Br, I), and heteroarenes. A successful synthesis of arylated stibine 3 a in a scale of 34.77 g demonstrates high synthetic potential of this transformation. The formed stibines (R3 Sb) were then used for the palladium-catalyzed carbon-carbon bond forming reaction with aryl boronic acids [R-B(OH)2 ], giving biaryls with high selectivity, even the structures of two organomoieties (R and R') are very similar. Plausible catalytic pathways were proposed based on control experiments.

Electron injection for aromatic metamorphosis of indole

AbstractAromatic metamorphosis, endocyclic transformations of aromatic compounds, has been emerging as a new synthetic strategy in organic synthesis. This counterintuitive strategy necessitates very powerful reactions that can surmount aromaticity and the strong carbon–heteroatom bonds of the heteroaromatic rings. This Short Account describes the development of the currently most powerful elementary reaction for aromatic metamorphosis, which is electron injection from lithium metal. Exceptionally robust and aromatic N‐phenylindole is subjected to the electron injection, resulting in the formation of the corresponding dianionic intermediate through reductive ring‐opening. A trapping reaction of the dianionic intermediate with organoboronic acid pinacol esters provides benzazaborines, which are attractive BN‐isosteres of naphthalenes. The electron injection helps establishing aromatic metamorphosis as a reliable synthetic methodology to provide novel useful molecules.