Vinyl Boronates Research Articles

Iron-Catalyzed Deboronation/Cyanoalkylation of Vinyl Boronic Acids with Cyclobutanone Ketoximes

AbstractIn this paper, an iron-catalyzed deboronation/cyanoalkylation of vinyl boronic acids for the preparation of distal cyanoalkyl alkenes with vinyl boronic acids as radical acceptor and activator is reported. In this reaction, various cyclobutanone oximes and substituted vinyl boronic acids can be transformed into the corresponding cyanoalkylated alkenes in moderate to good yields under these conditions. Mechanistic studies indicated that a single-electron transfer process may be involved in this transformation.

Regioselective Synthesis of α-Vinyl Boronates via a Pd-Catalyzed Mizoroki-Heck Reaction.

We report a palladium-catalyzed synthesis of α-vinyl boronates via a regioselective Mizoroki-Heck reaction between aryl triflates and vinyl boronates. This selectivity is achieved by the use of a 1,5-diaza-3,7-diphosphacyclooctane (P2N2) ligand, which results in minimal formation of the more commonly observed (linear) β-product. The choice of base, solvent, and presence of water are shown to be critical for controlling this outcome, with organic bases, nonpolar solvents, and anhydrous conditions favoring the Heck product and suppressing the competitive Suzuki-Miyaura coupling product.

Title Selective Coupling of β-(Borylvinyl)silanes by a Gold-catalyzed Hiyama Reaction - An Easy Way to Diaryl-Substituted Vinyl Boronates.

Diaryl-substituted vinyl boronates as potent building modules are challenging to synthesize. Herein, we present a convenient strategy based on a gold-catalyzed Hiyama arylation of (Z)-β-(borylvinyl)silanes which are easily accessible by hydroboration of silylalkynes. By exploiting the highly electronegative nature of the Au(III) intermediate (which is accessed by the light-assisted oxidation with aryl diazonium salts), a selective activation of the silyl group in the presence of the boron moiety is achieved. This opens a route to selectively synthesize diaryl-substituted vinyl boronates. The reaction shows a broad substrate range, excellent functional group tolerance and perfect chemo-selectivity. Experimental studies and DFT calculations allowed us to elucidate the mechanism of the reaction, the synthetic potential was demonstrated by downstream transformations providing a facile route to bifunctional phenanthrenes and triaryl-substituted olefins.

Paired Electrolysis Enables Reductive Heck Coupling of Unactivated (Hetero)Aryl Halides and Alkenes.

The formation of carbon-carbon (C-C) bonds is a cornerstone of organic synthesis. Among various methods to construct Csp2-Csp3 bonds, the reductive Heck reaction between (hetero)aryl halides and alkenes stands out due to its potential efficiency and broad substrate availability. However, traditional reductive Heck reactions are limited by the use of precious metal catalysts and/or limited aryl halide and alkene compatibility. Here, we present an electrochemically mediated, metal- and catalyst-free reductive Heck reaction that tolerates both unactivated (hetero)aryl halides and diverse alkenes such as vinyl boronates and silanes. Detailed electrochemical and deuterium-labeling studies support that this transformation likely proceeds through a paired electrolysis pathway, in which acid generated by the oxidation of N,N-diisopropylethylamine (DIPEA) at the anode intercepts an alkyl carbanion formed after radical-polar crossover at the cathode. As such, this approach offers a sustainable method for the construction of Csp2-Csp3 bonds from (hetero)aryl halides and alkenes, paving the way for the development of other electrochemically mediated olefin difunctionalization reactions.

Paired Electrolysis Enables Reductive Heck Coupling of Unactivated (Hetero)Aryl Halides and Alkenes

AbstractThe formation of carbon‐carbon (C−C) bonds is a cornerstone of organic synthesis. Among various methods to construct Csp2−Csp3 bonds, the reductive Heck reaction between (hetero)aryl halides and alkenes stands out due to its potential efficiency and broad substrate availability. However, traditional reductive Heck reactions are limited by the use of precious metal catalysts and/or limited aryl halide and alkene compatibility. Here, we present an electrochemically mediated, metal‐ and catalyst‐free reductive Heck reaction that tolerates both unactivated (hetero)aryl halides and diverse alkenes such as vinyl boronates and silanes. Detailed electrochemical and deuterium‐labeling studies support that this transformation likely proceeds through a paired electrolysis pathway, in which acid generated by the oxidation of N,N‐diisopropylethylamine (DIPEA) at the anode intercepts an alkyl carbanion formed after radical‐polar crossover at the cathode. As such, this approach offers a sustainable method for the construction of Csp2−Csp3 bonds from (hetero)aryl halides and alkenes, paving the way for the development of other electrochemically mediated olefin difunctionalization reactions.

Radical Polymerization of Vinyl Boronate Involving Backbiting Chain Transfer and Postpolymerization Oxidation Affording Branched Poly(vinyl alcohol)s

Radical Polymerization of Vinyl Boronate Involving Backbiting Chain Transfer and Postpolymerization Oxidation Affording Branched Poly(vinyl alcohol)s

Correction to “Facile Synthesis of Vinyl Boronate Esters via Dehydrogenative Borylation of Alkenes Enabled by Co-MOF Catalyst: An Additive Free Approach”

Correction to “Facile Synthesis of Vinyl Boronate Esters via Dehydrogenative Borylation of Alkenes Enabled by Co-MOF Catalyst: An Additive Free Approach”

Wittig-Type E-Selective Olefination of Imines with Vinyl Boronate Esters Under Copper Hydride Catalysis

Wittig-Type E-Selective Olefination of Imines with Vinyl Boronate Esters Under Copper Hydride Catalysis

Facile Synthesis of Vinyl Boronate Esters via Dehydrogenative Borylation of Alkenes Enabled by a Co-MOF Catalyst: An Additive-Free Approach

Facile Synthesis of Vinyl Boronate Esters via Dehydrogenative Borylation of Alkenes Enabled by a Co-MOF Catalyst: An Additive-Free Approach

Borylated cyclobutanes via thermal [2 + 2]-cycloaddition.

A one-step approach to borylated cyclobutanes from amides of carboxylic acids and vinyl boronates is elaborated. The reaction proceeds via the thermal [2 + 2]-cycloaddition of in situ-generated keteniminium salts.

Enantiospecific Synthesis of 1,3‐Disubstituted Allenes from Propargylic Carbonates through a Borylation‐1,2‐Elimination Process

AbstractAn array of enantioenriched vinyl boronates bearing an allylic carbonate moiety have been prepared through selective hydroboration of propargyl carbonates. Treatment of these vinyl boronates with TBAF in THF affords enantioenriched 1,3‐disubstituted allenes through a novel 1,2‐anti elimination in good yields and high enantiospecificities.

Rh-Catalyzed Borylative Cyclization of Acrylate-Containing 1,6-Enynes.

A Rh-catalyzed regioselective, stereoselective carbocyclization/borylation of acrylate-containing 1,6-enynes was described, which offers a general and practical method for constructing versatile and densely functionalized pyrrolidines with the (Z) geometry or the uncommon (E) geometry at the double bond with different substituents of the alkyne, with sterically hindered and conjugative aryl groups favoring the latter, featuring a tetrasubstituted vinyl boronate, containing an all-carbon quaternary stereocenter.

Asymmetric Synthesis of β-Aminoboronates via Copper-Catalyzed Reductive Coupling of Vinyl Boronates with Imines.

We report a copper-catalyzed asymmetric reductive coupling of vinyl boronates with imines, which directly access enantiomerically enriched β-aminoalkylboronates. Stereoselective addition of the in situ generated chiral α-borylalkyl copper to N-phosphinoyl imines provided target products in good yields with high diastereo- and enantioselectivity. Vinyl boronate with methylated acenaphthoquinone as a boron ligand was essential to efficiently spawn asymmetric products, and organic transformations of the boron moiety, along with the easily removable N-protecting group, proved their synthetic utility.

Regioselective Hydroalkylation of Vinyl- and Allylsilanes as Well as Vinylgermanes under Ni-H Catalysis.

A Ni-H-catalyzed hydroalkylation of vinylsilanes and -germanes as well as allylsilanes with unactivated alkyl iodides is reported. Unlike related reactions of styrene or vinyl boronate esters, the addition across the C-C double bond proceeds with anti-Markovnikov selectivity to deliver the linear regioisomer. Mechanistic control experiments support a radical mechanism, and a competition experiment reveals that the chemoselectivity is in favor of the vinyl over the allyl group.

Understanding the Mechanism and Selectivity of 1,1-Diborylalkanes from Alkenes Catalyzed by a Zirconium Complex.

The synthesis of 1,1-diborylalkanes from readily available alkenes is an appealing method. The density functional theory (DFT) method was employed to investigate the reaction mechanism of 1,1-diborylalkanes, which was synthesized from alkenes and a borane, and the reaction was catalyzed by a zirconium complex Cp2ZrCl2. The entire reaction is divided into two cycles: dehydrogenative boration to form vinyl boronate esters (VBEs) and hydroboration of VBEs. This article focuses on the hydroboration cycle and elaborates on the role of the reducing reagents in the equilibrium of self-contradictory reactivity (dehydrogenative boration and hydroboration). The H2 and HBpin pathways were investigated as the reducing reagents in the hydroboration process. The calculated results showed that it is more advantageous to use H2 as a reducing agent (path A). Furthermore, the σ-bond metathesis is the rate-determining step (RDS) with an energetic span of 21.4 kcal/mol. This is consistent with the self-contradictory reactivity balance proposed in the experiment. The reaction modes of the hydroboration process were also discussed. These analyses revealed the origin of selectivity in this boration reaction, in which the σ-bond metathesis of HBpin needs to overcome the strong interaction between HBpin and the Zr metal. Meanwhile, the origin of the selectivity of different positions of H2 is the interaction between the σ(H1-H2) → σ*(Zr1-C1) overlap and these findings have implications for catalyst design and application.

Nickel Phosphite-Catalyzed Tetradehydro-Diels-Alder Reactions of (E)-3-ene-1,8-diynes.

A nickel-catalyzed tetradehydro-Diels-Alder reaction of (E)-3-ene-1,8-diynes for the preparation of isoindolines, dihydroisobenzofurans, and tetrahydroisoquinolines has been developed. A series of air-stable nickel catalysts were used in this study, including the novel nickel(0)-phosphite catalysts, Ni[P(O-3,5-Me-Ph)3]4, Ni[P(O-1-naphthyl)3]4, and Ni[P(O-2-naphthyl)3]4. To help understand the type of intermediate in the initial cycloisomerization process, the trapping of nickellacycle intermediates with pinacolborane to yield vinyl boronates is also discussed.

Visible‐Light‐Promoted Reaction ofN‐Hydroxyphthalimide Esters with Vinyl Boronic Pinacol Ester

AbstractA novel and easy‐to‐execute light‐driven protocol for the preparation of alkyl boronic acid pinacol esters from vinyl boronate usingN‐hydroxyphthalimide esters as the potential precursor is described. In this photochemical protocol, theN‐hydroxyphthalimide ester's fragmentation generates C‐centered radicals, which undergo a radical Michael addition to vinyl boronic pinacol ester furnishing the desired products. A good substrate scope having various functionalities is presented and good to high yields are obtained.

Regio- and Stereoselective Carbon-Boron Bond Formation via Heterogeneous Palladium-Catalyzed Hydroboration of Enallenes.

A highly efficient regio- and stereoselective heterogeneous palladium-catalyzed hydroboration reaction of enallenes was developed. Nanopalladium immobilized on microcrystalline cellulose (MCC) was successfully employed as an efficient catalyst for the enallene hydroboration reaction. The nanopalladium particles were shown by HAADF-STEM to have an average size of 2.4 nm. The cellulose-supported palladium catalyst exhibits high stability and provides vinyl boron products in good to high isolated yields (up to 90 %). The nanopalladium catalyst can be efficiently recycled and it was demonstrated that the catalyst can be used in 7 runs with a maintained high yield (>80 %). The vinylboron compounds prepared from enallenes are important synthetic intermediates that can be used in various organic synthetic transformations.

CeO2‐Nanorods‐Catalyzed Protoboration of Alkenes and Alkynes with Bis(pinacolato)diboron

AbstractThe protoboration of alkenes and alkynes with B2pin2 (pin=OCMe2CMe2O) using a heterogeneous CeO2 nanorods catalyst has been developed to afford the corresponding alkyl and vinyl boronate esters in 41–99% yield under mild reaction conditions. A series of aromatic and aliphatic alkenes and alkynes with synthetically important functional groups were well tolerated. In both the systems, the catalyst could be reused for up to six runs without significant loss in activity. Stoichiometric reactions revealed that the protoboration may proceed through the in situ formed catalytically active boryl species.magnified image

Mechanistic Insights into the Metal-Free Deoxygenative Borylation of Ketones and Aldehydes with Bis(catecholato)diborane.

The mechanisms of direct deoxygenative borylation of acetone and benzaldehyde with bis(catecholato)diborane (B2 cat2 ) in the solvent N,N-dimethylacetamide (DMA) are investigated through detailed density functional theory calculations. These calculations show that the isomer 1,2-B2 cat2 in situ generated from 1,1-B2 cat2 induced by DMA is the reactive boron intermediate for the reactions. The addition of the B-B bond of 1,2-B2 cat2 to the C=O bond of acetone or benzaldehyde via a concerted [2σ+2π]-cycloaddition-like transition state is the rate-limiting step for both the triboration reaction of acetone and the monoboration reaction of benzaldehyde. DMA not only acts as the solvent but also promotes the structural isomerization of B2 cat2 , the deoxygenation of acetone to form the vinyl boronate intermediate and subsequent diboration of vinyl boronate with 1,2-B2 cat2 , as well as the protodeboronation of the gem-diboronate intermediate in the deoxygenative borylation of benzaldehyde. The presented computational results can explain the observed experimental facts and provide insight into the roles of the isomeric 1,2-B2 cat2 and the solvent DMA in related reactions.