Boronic Coupling Research Articles

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.

An Alternative Route to Complex Allenes or Cyclooctatrienes via a Suzuki Cyclocarbopalladation Cascade.

The 4-exo-dig cyclocarbopalladation of vinyl bromides substituted with a triple or double bond resulted in impressive cascade reactions leading to different compounds under Suzuki cross-coupling conditions upon a slight modification of the starting material. When the starting compound carries a triple bond, a single cascade occurs providing a structure containing an allene, a tetrasubstituted cyclopropane, and a cyclobutene with complete stereoselectivity. When the related starting material possessing a double bond is reacted under the same conditions in the presence of various vinyl boronic esters or acids, an efficient 8π-electrocyclization provides tricyclic systems comprised of a cyclobutene unit, as well as a cyclooctatriene. Five carbons of the latter can be selectively decorated with different substituents depending on the choice of the starting material and the boronic coupling partner.

Ligand Effects in Carbon−Boron Coupling Processes Mediated by σ‐BH Platinum Complexes

AbstractThe reaction of tri‐coordinated boranes (derived from dioxaborolanes and diazaborolanes) with cyclometalated low‐electron count platinum complexes [Pt(NHC’)(NHC)][BArF] (NHC=ItBuiPr, IMes, IMes*) led, at low temperature, to the formation of the corresponding σ‐BH species. Some of these species have been characterized by X‐Ray diffraction methods showing a rare η1‐coordination mode. These compounds are thermally unstable and undergo a carbon‐boron coupling process whose reversibility depends on the NHC ligand. DFT calculations indicate that the energy barriers required for C−B bond formation events (together with Pt−H bonds) are lower than the competitive reactions leading to C−H bond formation (and Pt−B bonds). However, the C−B coupling products appear to be formed under kinetic control with ItBuiPr ligands, whereas the relative low energy barrier leading to C−H bond formation is sufficiently low to form the thermodynamically more stable platinum boryl complexes at rt. The latter energy barrier is, nevertheless, too high for the systems bearing IMes and IMes* ligands.

Controlled Access to C1‐Symmetrical Cyclotriveratrylenes (CTVs) by Using a Sequential Barluenga Boronic Coupling (BBC) Approach

AbstractWe describe here a controlled approach to C1‐symmetrical cyclotriveratrylenes (CTVs). In this approach dimers are synthesized through Barluenga boronic coupling (BBC) and after borylation, the last aromatic ring is introduced by a second BBC. After functional transformations of the trimers, the CTVs are formed using intramolecular SEAr.magnified image

MIDA boronate allylation - synthesis of ibuprofen.

MIDA boronates are among the most useful reagents for the Suzuki–Miyaura reaction. This chemistry typically generates new bonds between two aromatic rings, thereby restricting access to important areas of chemical space. Here we demonstrate the coupling of MIDA boronates to allylic electrophiles, including a new synthesis of the well-known COX inhibitor ibuprofen.

Synchronous improvement of electrical and mechanical performance of A356 alloy reinforced by boron coupling nano-AlNp

High strength and excellent electrical conductivity of Al alloys are highly desired in the field of power transmission. However, these two factors are usually contradictory in metallic materials. A novel boron coupling nano-AlN particles (about 0.6 wt% nano-AlNp and 0.06 wt% B) reinforced A356 alloy is proposed in this paper, which obtains excellent electrical conductivity (σ: 46.2% IACS), high ultimate tensile strength (UTS: 300 MPa), superior yield strength (YS: 240 MPa) and good elongation (EL: 7.5%) synchronously. Contrasting with the general A356 alloy modified by Sr, the σ, UTS, YS, and EL increased by about 8.2%, 9.1%, 4.3% and 66.7% respectively. This strategy is mainly based on boron treatment and nano-AlNp inhibiting the lapped growth of eutectic Si to ensure high conductivity, and the modification of Si, the refinement of the SDAS of α-Al grains and the relative homogeneous distribution of the individual or small flocculent nano-AlNp in the matrix and at the Al/Si interface to ensure high mechanical properties.

PEG-mediated recyclable borylative coupling of vinyl boronates with olefins

This paper reports on the first green and sustainable repetitive batch borylative coupling of vinyl boronates with olefins by the effective immobilization of the [Ru(CO)Cl(H)(PCy3)2] catalyst in poly(ethylene glycols) with different molecular weights (Mw = 600–2000) and ending groups (OH, OMe, OSiMe3) or in biphasic poly(ethylene glycols)/supercritical CO2 (PEGs/scCO2) systems. Within this process, (E)-alkenyl boronates were obtained with high yields and excellent stereo-, regioselectivities. The best strategies permitted to carry out cross-coupling of vinyl boronates with styrene for up to 8–16 repetitive batches respectively, by applying 2 or 4 mol% of Ru-catalyst. The described methods enable the reuse of the TM-catalyst and solvents and the reduction or elimination of the use of volatile organic solvents and metal content in the final products, and obtain high cumulative TON values (up to 440). The biphasic systems also allowed the simplification of the separation procedure by effective product extraction in CO2 stream.

Gold‐Catalyzed Direct Oxidative Arylation with Boron Coupling Partners

AbstractAn efficient synthesis of biaryls through a gold‐catalyzed oxidative cross‐coupling of arenes with strong electron‐deprived aryl boronates is presented herein. Regio‐ and chemocontrol are achieved by the selective activation of these coupling partners by gold at different oxidation states. Under reaction conditions devoid of basic additives or directing groups, the role of acetato ligand as an internal base has been revealed as a key parameter for expanding the reaction scope in these transformations.

Gold-Catalyzed Direct Oxidative Arylation with Boron Coupling Partners.

An efficient synthesis of biaryls through a gold-catalyzed oxidative cross-coupling of arenes with strong electron-deprived aryl boronates is presented herein. Regio- and chemocontrol are achieved by the selective activation of these coupling partners by gold at different oxidation states. Under reaction conditions devoid of basic additives or directing groups, the role of acetato ligand as an internal base has been revealed as a key parameter for expanding the reaction scope in these transformations.

Direct Access to α,α-Difluoroacylated Arenes by Palladium-Catalyzed Carbonylation of (Hetero)Aryl Boronic Acid Derivatives.

A palladium-catalyzed carbonylative coupling of (hetero)aryl boronates or boronic acid salts with carbon monoxide and α-bromo-α,α-difluoroamides and bromo-α,α-difluoroesters is described herein. The method is useful for the synthesis of a diverse selection of (hetero)aryl α,α-difluoro-β-ketoamides and α,α-difluoro-β-ketoesters, which are useful building blocks for the generation of functionalized difluoroacylated and difluoroalkyl arenes. The method could be further extended to a one-pot protocol for the formation of difluoroacetophenones.

Direct Access to α,α‐Difluoroacylated Arenes by Palladium‐Catalyzed Carbonylation of (Hetero)Aryl Boronic Acid Derivatives

AbstractA palladium‐catalyzed carbonylative coupling of (hetero)aryl boronates or boronic acid salts with carbon monoxide and α‐bromo‐α,α‐difluoroamides and bromo‐α,α‐difluoroesters is described herein. The method is useful for the synthesis of a diverse selection of (hetero)aryl α,α‐difluoro‐β‐ketoamides and α,α‐difluoro‐β‐ketoesters, which are useful building blocks for the generation of functionalized difluoroacylated and difluoroalkyl arenes. The method could be further extended to a one‐pot protocol for the formation of difluoroacetophenones.

Orthogonally Reacting Boron Coupling Reagents: A Novel Multicomponent-Multicatalytic Reaction [(MC)2R] of Dichlorovinylpyrazine

The results presented herein illustrate the feasibility of two orthogonally reacting boron coupling reagents as a new control strategy in multicomponent-multicatalytic reaction [(MC)2R] chemistry. A process employing dichlorovinylpyrazine merging the rhodium-catalyzed hydroarylation with the Suzuki coupling has been discovered. Three new bonds are formed in a one-pot, one-step process efficiently providing highly substituted diaza-dihydrodibenzoxepine products.

B–H Bond Cleavage via Metal–Ligand Cooperation by Dearomatized Ruthenium Pincer Complexes

Organic derivatives of boronic acid are widely used reagents useful in various synthetic applications. A fundamental understanding and the exploration of new reaction pathways of boronic reagents with organometallic systems hold promise for useful advancement in chemical catalysis. Herein we present the reactions of simple boranes with dearomatized ruthenium pincer complexes based on PNP (2,6-bis(di-tert-butylphosphinomethyl)pyridine) or PNN (2-(di-tert-butylphosphinomethyl)-6-(diethylaminomethyl)pyridine) ligands. NMR studies revealed dehydrogenative addition of the borane B–H bond across the metal center and the ligand. Remarkably, new complexes were observed, which contain the boryl moiety at the benzylic carbon of the pincer ligand arm. X-ray crystal structures of new dearomatized boryl pincer complexes were obtained, and DFT calculations revealed mechanistic details of the adduct formation process through a dehydrogenative pathway. In addition, catalytic aryl–boron coupling reactions were explored. T...

A boron–boron coupling reaction between two ethyl cation analogues

The design of larger architectures from smaller molecular building blocks by element-element coupling reactions is one of the key concerns of synthetic chemistry, so a number of strategies were developed for this bottom-up approach. A general scheme is the coupling of two elements with opposing polarity or that of two radicals. Here, we show that a B-B coupling reaction is possible between two boron analogues of the ethyl cation, resulting in the formation of an unprecedented dicationic tetraborane. The bonding properties in the rhomboid B₄ core of the product can be described as two B-B units connected by three-centre, two-electron bonds, sharing the short diagonal. Our discovery might lead the way to the long sought-after boron chain polymers with a structure similar to the silicon chains in β-SiB₃. Moreover, the reaction is a prime textbook example of the influence of multiple-centre bonding on reactivity.

Application of Barluenga Boronic Coupling (BBC) to the Parallel Synthesis of Drug‐like and Drug Fragment‐like Molecules

BBC news: CC bond formation reactions are underused by medicinal chemists for the preparation of libraries of compounds with good drug-like (“rule-of-five”) and drug fragment-like (“rule-of-three”) properties. Herein we demonstrate the versatility of the Barluenga boronic coupling (BBC) for the preparation of small drug-like and drug fragment-like compounds in parallel.

Expanding the scope of the Cu assisted Suzuki–Miyaura reaction

Recent advances in the development of the copper facilitated Suzuki–Miyaura reaction are described. Improvements include expansion of substrate scope to include aryl chlorides and polyhalo aryl boronates. It was found that use of S-Phos and X-Phos could accomplish the coupling of 2-pyridyl boronates to aryl chlorides and bromides in shorter reaction times and in higher yield than previously described with DPPF.

ChemInform Abstract: Copper‐Promoted Coupling of Vinyl Boronates and Alcohols: A Mild Synthesis of Allyl Vinyl Ethers.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Allyl Vinyl Ethers by Copper-Promoted Coupling of Vinyl Boronates to Alcohols

A cross-coupling methodology for the synthesis of allyl vinyl ethers from vinyl boronates and allylic alcohols mediated by Cu(OAc)2 is reported and a plausible reaction mechanism is presented. A variety of functional groups is tolerated, such as acetals, esters or sulfides.

Copper-Promoted Coupling of Vinyl Boronates and Alcohols: A Mild Synthesis of Allyl Vinyl Ethers

A copper-promoted coupling of vinyl pinacol boronate esters and alcohols for the synthesis of enol ethers is reported. The reaction occurs in 50-99% yield and is compatible with a variety of functional groups. Cupric acetate is the copper source, and triethylamine buffer is used to prevent protodeboration; the reaction occurs at room temperature. In addition to excellent chemoselectivity, the reaction is stereospecific.

Copper-Facilitated Suzuki Reactions: Application to 2-Heterocyclic Boronates

The palladium-catalyzed Suzuki-Miyaura reaction has been utilized as one of the most powerful methods for C-C bond formation. However, Suzuki reactions of electron-deficient 2-heterocyclic boronates generally give low conversions and remain challenging. The successful copper(I) facilitated Suzuki coupling of 2-heterocyclic boronates that is broad in scope is reported. Use of this methodology affords greatly enhanced yields of these notoriously difficult couplings. Furthermore, mechanistic investigations suggest a possible role of copper in the catalytic cycle.