Glucose‐induced and fructose‐induced deboronation reaction of 4‐mercaptophenylboronic acid assembled on silver investigated by surface‐enhanced Raman scattering

We examined the deboronation reaction of 4‐mercaptophenylboronic acid (4MPBA) via fructose and glucose on silver surfaces by means of surface‐enhanced Raman scattering (SERS) at the excitation wavelengths of 488, 514, and 633 nm. The SERS spectra on silver nanoparticles clearly exhibited specific spectral signatures of thiophenol (TP) peaks, indicating a deboronation reaction of 4MPBA on the surfaces, whereas no strong TP peaks were observed on gold nanoparticles. The vibrational bands at 417, 999, 1021, and 1574 cm^?1 in the Ag SERS spectra could correspond to the in‐plane aromatic ring modes in TP. X‐ray photoelectron spectroscopy also supported the surface reaction on Ag by referring the B1s peaks at ~193 eV. The ratiometric Raman measurements of the band at 1574 cm^?1, with respect to that at 1587 cm^?1, revealed fructose and glucose quantification in the concentration range of 1–10 mm . We did not identify such changes for mannose, sucrose, and sialic acid. The SERS peaks of 4MPBA on roughened Ag plates also exhibited TP bands to show the time‐dependent spectral change. Our findings indicate that the deboronation of 4MPBA and conjugation with fructose and glucose may be facilitated efficiently on silver surfaces for their quantification. Copyright © 2016 John Wiley & Sons, Ltd.     

Dicarba-closo-dodecaborane(12) derivatives of phosphonium salts: easy formation of nido-carborane phosphonium zwitterions

The first examples of arylphosphonium salts containing a dicarba-closo-dodecaborane(12) (closo-carborane) are reported; in contrast to the 1,12-carborane derivative, the 1,2- and 1,7-isomers undergo a facile deboronation reaction in polar solvents to afford the corresponding nido-carborane phosphonium zwitterions.     

Rhodium-catalysed addition of arylboronic acids to oxabenzonorbornadienes

The facile addition reaction of boronic acids to oxabenzonorbornadienes was achieved using a catalytic amount of a rhodium(I) complex having P(OEt)3 ligands, affording cis-2-aryl-1,2-dihydro-1-naphthol stereoselectively, and in good yield without concomitant deboronation of the boronic acid.     

Real-time monitoring of microwave-promoted Suzuki coupling reactions using in situ Raman spectroscopy

The progress of microwave-promoted Suzuki reactions has been monitored using an in situ Raman spectroscopy apparatus assembled from commercially available components. It was possible to see if any reaction occurred and, if so, when it reached completion. In addition, the monitoring technique has given us an insight into the reaction, confirming that, when run in aqueous media, the coupling is in competition with the rapid deboronation of the boronic acid.     

In Situ Generated Palladium Nanoparticles for Catalytic Dehalogenation of Aryl Halides and Deboronation of Arylboronic acids

Palladium nanoparticles in situ generated from palladacyclic complexes efficiently catalyzed the deboronation of arylboronic acids and the dehalogenation as well as homo‐coupling of aryl iodides in an alcohol medium under basic conditions. Isotope labeled studies indicated that the β‐elimination of alcohols provided the hydrogen source for the reaction.     

In situ Raman spectroscopy as a probe for the effect of power on microwave-promoted Suzuki coupling reactions

We report the use of in situ Raman spectroscopy as a probe for the effect of power on microwave-promoted Suzuki coupling reactions. We find that increased initial microwave power leads to greater acceleration of the reaction but that the product yield obtained is essentially independent of initial microwave power. The application of simultaneous cooling lengthens the reaction time but does not alter the relative rates of the Suzuki coupling and deboronation processes. Performing the reaction at an initial microwave power of 5 W leads to an improvement in product yield.     

Application of the Suzuki reaction as the key step in the synthesis of a novel atropisomeric biphenyl derivative for use as a liquid crystal dopant

A heavily functionalized atropisomeric biphenyl derivative (4), which is designed to possess a large lateral dipole moment, has been synthesized with use of a Suzuki coupling as the key step and resolved by chiral HPLC. The final coupling reaction is complicated by rapid hydrolytic deboronation of the sterically hindered, electron poor boronate 22. Rigorously anhydrous conditions are therefore necessary to achieve the coupling.     

Hypervalent Iodine Reagents Enable Chemoselective Deboronative/Decarboxylative Alkenylation by Photoredox Catalysis

Chemoselective C(sp³)? C(sp²) coupling reactions under mild reaction conditions are useful for synthesizing alkyl‐substituted alkenes having sensitive functional groups. Reported here is a visible‐light‐induced chemoselective alkenylation through a deboronation/decarboxylation sequence under neutral aqueous reaction conditions at room temperature. This reaction represents the first hypervalent‐iodine‐enabled radical decarboxylative alkenylation reaction, and a novel benziodoxole‐vinyl carboxylic acid reaction intermediate was isolated. This C(sp³)? C(sp²) coupling reaction leads to aryl‐and acyl‐substituted alkenes containing various sensitive functional groups. The excellent chemoselectivity, stable reactants, and neutral aqueous reaction conditions of the reaction suggest future biomolecule applications.     

Synthesis and reactivity of 4,5-[1,2-dicarba-closo-dodecaborano(12)]-1,3-diselenacyclopentane: opening of the icosahedron to give a zwitterionic intermediate and conversion into 7,8-dicarba-nido-undecaborate(1-)

The reaction of the 1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion [1,2-(1,2-C(2)B(10)H(10))Se(2)](2-) with dichloromethane (CH(2)Cl(2) or CD(2)Cl(2)) in the presence of donor solvents gave 4,5-[1,2-dicarba-closo-dodecaborano(12)]-1,3-diselenacyclopentane, the title compound, which was characterized by X-ray structural analysis and NMR spectroscopy ((1)H, (11)B, (13)C, and (77)Se). In the presence of pyridine, opening of the icosahedron took place, and a zwitterionic intermediate was isolated and fully characterized in the solid state by X-ray diffraction and in solution by multinuclear magnetic resonance techniques. Although such types of intermediates, prior to deboronation of the ortho-carborane cage, have been proposed several times, this is first example for which the structure has been confirmed unambiguously. This intermediate possesses a nido structure and contains a 7,8-dicarba-nido-undecaborate(1-) anion and a boronium cation, the latter with two pyridine rings linked to the boron atom, which has been extruded from the cage. It was shown that this process is reversible as long as the deboronation is not complete. The formation of the intermediate is accompanied by deboronation, which leads to the 7,8-dicarba-nido-undecaborate(1-) anion. The latter was prepared independently by conventional routes from the title compound, isolated as crystalline material as the tetrabutyl ammonium salt, and characterized by X-ray structural analysis and multinuclear magnetic resonance spectroscopy ((1)H, (11)B, (13)C, and (77)Se).     

Synthesis of chiral binaphthalenes using the asymmetric Suzuki reaction

The synthesis of atropisomeric 1,1′-binaphthalenes can be achieved using an asymmetric Suzuki cross-coupling reaction. The Suzuki reaction leading to such hindered compounds is challenging and competing hydrolytic deboronation frequently dominates unless carefully chosen conditions are employed. The simple, standard mechanism is inadequate when describing the Suzuki coupling of hindered partners. Evidence suggests that the key step leading to asymmetry is transmetallation (delivery of the organometallic by the asymmetric ligand) and the reactions operate under kinetic control. Reductive elimination (itself likely to be triggered by oxidative addition of another molecule of halide) is fast compared with equilibration (epimerisation and/or cis-trans isomerisation).     

Identification of an intermediate in the deboronation of ortho-carborane: an adduct of ortho-carborane with two nucleophiles on one boron atom

The 1 : 2 adduct of 1-bromo-ortho-carborane and pyridine has been identified as a significant intermediate in the deboronation of ortho-carborane to a nido-anion.     

Palladium complexes with abnormal N-heterocyclic carbene ligands derived from 1,2,3-triazolium ions and their application in Suzuki coupling

Chiral and achiral pincer type palladium complexes bearing abnormal N-heterocyclic carbene ligands derived from 1,2,3-triazole are reported. Both complexes are effective as catalysts for non-asymmetric Suzuki coupling reaction for the synthesis of biphenyl derivatives. However, both the complexes failed to catalyze the formation of binaphthyl derivatives, by the asymmetric Suzuki coupling in case of the chiral complex and the non-asymmetric version in case of the achiral pincer complex. Instead deboronation of arylboronic acid occurred very efficiently leaving the aryl bromide intact.     

Synthesis of cobalt and nickel 6,6′-diphenylbis(dicarbollides)

Russian Chemical Bulletin - 6,6′-Diphenyl derivatives of cobalt and nickel bis(dicarbollide) were synthesized starting from nido-carborane by the insertion—deboronation—insertion...     

Conjugates of polyhedral boron compounds with carbohydrates 7. Hydrolytic stability of closo-ortho-carborane glycoconjugates containing from one to three β-lactosylamine and β-d-galactopyranosylamine residues; estimation of their galectin-binding efficiency with galectin RCA120

The galectin-binding efficiency (Ricinus communis agglutinin, RCA) and the degree of deboronation at 37 °C of glycoconjugates of ortho-carboranylacetic acid containing from one to three β-lactosylamine or β-d-galactopyranosylamine residues were estimated; the glycoconjugates are potential agents for boron neutron capture therapy of cancer. Over a period of 24 h, up to ～15% of glycoconjugates underwent deboronation to give glycoconjugates of nido-ortho-carborane. With Lac-β-NH(COCH₂NH)₂COCH₂-o-CCHB₁₀H₁₀ as an example, it was demonstrated that the deboronation occurs at both 60 and 5 °C. Glycoconjugates with an O-linked β-galactose as a fragment of lactosylamine bind to galectin RCA₁₂₀ much more efficiently (up to ～40 times) than do the corresponding glycoconjugates with a N-linked β-galactose residue. The glycoconjugates containing one β-lactosylamine residue bind to galectin RCA approximately two times less efficiently than does lactose; however, introduction of the second and third β-lactosylamine residues into the glycoconjugate increases the binding efficiency by a factor of five to seven due to the cluster effect.     

Accessing the First nido-Carborane-Substituted Diphosphetane: A Ligand and Synthon for nido-Carboranylphosphanes

Deboronation of a carborane-substituted diphosphetane 2 in toluene yielded the first nido-carboranyldiphosphetane 1 . The P−P bond in 1 can be broken via dismutation reactions with diaryl dichalcogenides yielding nido-carboranyl bis-phosphanes that were not accessible via established synthetic protocols. Additionally, transition metal complexes of 1 could be isolated including one coordination polymer. Notably, when the deboronation of 2 is carried out in ethanol, unprecedented nido-carborane-substituted secondary bis-phosphane monoxides ( 3 , 4 ) are obtained. These compounds are interesting starting materials for further reactivity studies due to their P−H bonds. Experimental findings are supported by DFT calculations including the calculation of reaction mechanisms and NMR spectroscopic parameters.     

Intramolecular Communication in Anionic Oxidized Phosphanes through a Chelated Proton

Oxidation of the 1,2‐(PR₂)₂‐1,2‐closo‐C₂B₁₀H₁₀ (R=Ph, iPr) platform with hydrogen peroxide in acetone is a two‐step procedure in which partial deboronation of the closo cluster and oxidation of the phosphorus atoms occur. Based on NMR spectroscopic and kinetic data, we demonstrate that the phosphorus atoms are oxidized in the first step, followed by cluster deboronation. DFT calculations and natural‐bond orbital (NBO) analysis were used to obtain insight into the electronic structures of diphosphane ortho‐carborane derivatives.     

A new resorufin-based spectroscopic probe for simple and sensitive detection of benzoyl peroxide via deboronation

A new resorufin-based probe is developed, which exhibits a rapid and sensitive color and a fluorescence off-on response to benzoyl peroxide (BPO) in aqueous media containing 10% ethanol via deboronation. The probe has been applied to the simple detection of BPO in real samples such as wheat flour and antimicrobial agent.     

Synthesis of a (β-acetamido-α-acetoxyethyl)boronic ester via azido boronic esters

(Azidomethyl)boronic esters of 1,2-dicyclohexyl-1,2-ethanediol (“DICHED”) and pinanediol have been prepared from the corresponding (bromomethyl)boronic esters. Conversion to (2-azido-1-chloro- or bromoethyl)boronic esters by reaction with a (dihalomethyl)lithium followed. Attempted displacement of halide from DICHED (2-azido-1-haloethyl)boronates with alkoxides failed. Reaction of either pinanediol or DICHED (2-azido-1-chloromethyl)boronate with sodium acetate in acetic acid yielded the 1-acetoxy derivative as a ∼1:1 mixture of diastereomers, indicating probable involvement of an α-boryl carbocation intermediate. Hydrogenation of the pinanediol azido boronic ester over platinum in a solution of hydrogen chloride in dioxane was accompanied by deacetylation to form the impure (2-amino-1-hydroxyethyl)boronic ester hydrochloride. Attempted purification of this material resulted in deboronation to ethanolamine. Acetylation yielded pinanediol (2-acetamido-1-acetoxyethyl)boronate.     

On the scope of the Pt-catalyzed Srebnik diborylation of diazoalkanes. An efficient approach to chiral tertiary boronic esters and alcohols via B-stabilized carbanions

Conditions milder than those previously reported are shown to be generally applicable to the Pt-catalyzed insertion of non-carbonyl-stabilized diazoalkanes into B₂pin₂. Selective transformation of one (pinacolato)boryl unit in the products is enabled by rapid, low-temperature deboronation in the presence of a Lewis base and genesis of a highly reactive B-stabilized carbanion.     

Conjugates of polyhedral boron compounds with carbohydrates. 4. hydrolytic stability of carborane–lactose conjugates depends on the structure of a spacer between the carborane cage and sugar moiety

A novel 1,2‐dicarba‐closo‐dodecaborane–lactose conjugate ( 4a ) with an N‐glycosidic linkage was synthesized. This conjugate was found to be much more stable against hydrolytic deboronation (closo to nido tranformation of the carborane cage) under neutral conditions than a related carborane–lactose conjugate ( 1a ) with an O‐glycosidic linkage. This result demonstrates that the hydrolytic stability of carborane–carbohydrate conjugates in neutral aqueous solutions may depend dramatically on the chemical nature of the spacer that links the carbohydrate moiety with the boron cage, the rate of hydrolysis varying by orders of magnitude. We relate a significant decrease in the deboronation rate to the formation of more strongly bound supramolecular aggregates, in which the boron cage is less accessible to nucleophilic attack by solvent molecules, in the solution of the carborane–N‐lactoside conjugate 4a . Copyright © 2006 John Wiley & Sons, Ltd.