Microwave-accelerated derivatization processes for the determination of phenolic acids by gas chromatography-mass spectrometry

A rapid method for the derivatization of phenolic antioxidants using microwave irradiation has been developed. Six antioxidatively active phenolic components of wines and fruits, namely gallic acid, gentisic acid, vanillic acid, caffeic acid, ferulic acid and p-coumaric acid were used in the model study. The solution of phenolic acids was evaporated to dryness on a rotary evaporator followed by further drying under microwave irradiation (600 W, 30 s). The resultant residue was dissolved in pyridene and treated with bis(trimethylsilyl)acetamide while irradiated by microwave using high power for 30 s. Controlled reaction was carried out employing bis(trimethylsilyl)trifluoroacetamide under conventional heating for 30 min. The trimethylsilyl derivatives were identified and quantified on a gas chromatography/mass selective detector. The mass spectral fragmentation patterns of the derivatives obtained by microwave irradiation were identical to those prepared by heating. The yields of microwave-assisted silylation were comparable to those from conventional heating. The rsd were less than 8% for six replicates. The linearity in wine matrix was nearly perfect. This method is a useful protocol to examine the phenolic constituents in wines and agricultural products.     

A chemoselective deprotection of trimethylsilyl acetylenes catalyzed by silver salts

Trimethylsilyl acetylenes can be selectively deprotected in the presence of a catalytic amount of silver salts. AgNO₃ and AgOTf proved to be the most effective catalyst in a mixture of methanol, water and dichloromethane. Other functional groups, and especially silyl ethers, are not affected in these conditions.     

Efficient, highly regioselective, and stereospecific conversion of glycidol systems into C2-O-acylated vicinal halohydrins

Glycidyl esters and ethers undergo a regioselective and stereospecific opening of the oxirane ring upon treatment in chloroform in the presence of pyridine with trimethylsilyl halide (TMSX, X = Cl, Br, or I) and a mixture of carboxylic acid (CA)-trifluoroacetic anhydride (TFAA), to produce the corresponding C2-O-acylated vicinal halohydrins in high yields.     

Quantum-Chemical Investigation of Intermediates in the Addition of Phenylsulfenium Cation to Substituted Acetylenes

The reaction paths for the transformations of substituted acetylenes (X—CC—Y; X, Y = H, Me, Ph, CN) in reaction with phenylsulfenium cation were studied by quantum-chemical methods. It was shown that the reactions take place with the formation of acyclic and cyclic cationic intermediates. The factor that determines the structure and characteristics of these cations is the induction and polarizing action of the substituents in the acetylenes and to a lesser degree their electron-donor characteristics. The resonance effect of the phenyl substituent has a predominantly levelling action on the distribution of charges.     

Rhodium-catalyzed highly selective thioformylation of acetylenes with thiols and carbon monoxide

Highly regioselective thioformylation of terminal acetylenes with thiols and carbon monoxide has been developed by the use of rhodium(I) complexes as the catalyst: formyl and thio groups are introduced into the terminal and inner positions of acetylenes, respectively. The thioformylation is performed in the presence of a catalytic amount of rhodium(I) complexes, such as RhH(CO)(PPh₃)₃, RhCl(PPh₃)₃, and RhCl(CO)(PPh₃)₂, under the pressure of CO (3 MPa) at 120°C in CH₃CN to provide β-thio-α,β-unsaturated aldehydes in good yields. This thioformylation can be applied to a variety of terminal acetylenes and aromatic thiols. A mechanistic proposal includes the formation of the rhodium sulfide complex as the key species.     

A synthesis of pyrrolo[2,1-a]isoquinolines through the reaction of activated acetylenes and isoquinoline in the presence of ethyl bromopyruvate

Isoquinoline reacts with ethyl bromopyruvate in the presence of dialkyl acetylenedicarboxylates or diaryloylacetylenes to produce dialkyl 1-(2-ethoxy-2-oxoacetyl)pyrrolo[2,1-a]isoquinoline-2,3-dicarboxylates or ethyl 2-[2,3-diaryloylpyrrolo[2,1-a]isoquinoline-1-yl]-2-oxoacetates in good yields.     

Synthesis of bis(alk-3-en-1-ynyl)benzene with either E- or Z-configuration via a one-pot three-component coupling reaction and its optical properties

A convenient, efficient and stereoselective synthesis of a range of bis(alk-3-en-1-ynyl)benzenes with E- and Z-configuration is described. The protocol involves Cu-mediated cross-coupling reaction of (E)- and (Z)-alk-1-enyldisiamylboranes with (trimethylsilyl)ethynyl bromide and Pd/Cu-catalyzed cross-coupling reaction with diiodobenzene. The sequential cross-coupling reaction proceeds readily under extremely mild conditions in a one-pot manner to afford bis(alk-3-en-1-ynyl)benzenes in good to excellent yields. The optical properties of the products are also described.     

A new diphenylphosphinite ionic liquid (IL-OPPh2) as reagent and solvent for highly selective bromination, thiocyanation or isothiocyanation of alcohols and trimethylsilyl and tetrahydropyranyl ethers

A new diphenylphosphinite ionic liquid (IL-OPPh₂) is introduced. This ionic liquid is used as both a reagent and a solvent to convert alcohols and trimethylsilyl and tetrahydropyranyl (THP) ethers into their corresponding alkyl bromides, thiocyanates or isothiocyanates in the presence of Br₂ and SCN⁻ at 80 °C. In this ionic liquid, bromination and thiocyanation of alcohols occurs highly selectively in the presence of trimethylsilyl and THP-ethers and also between different classes of alcohols. The use of this ionic liquid allows easy separation of the desired products from the phosphinate by-product.     

Influence of solvents on the insertion of methacrolein into zirconacyclopropenes

The reaction of Cp₂Zr(L)(η²-Me₃SiC₂) (L = THF, py) with equimolar amounts of H₂C = CMe-CHO at room temperature depends strongly on the ligands L and the solvents that are used. With L = THF, in the THF solution the insertion product

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1 was isolated, whereas by conducting the reaction in n-hexane solution an alkyne substitution with 1,4-coordination of the methacrolein takes place and the binuclear complex [

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2 was obtained. In conttrast, with L = py (a stronger ligand) only a 1:1 ratio of 1 and 2 was observed in both THF and in n-hexane. At 50°C complex 1 was converted into 2 and the alkyne was eliminated quantitatively.

Complexes 1 and 2 were characterized by IR and NMR spectroscopical measurements and 1 by an additional X-ray structure determination.     

Electrochemically formed fullerene-based polymeric films

The recent results of investigations involving the electrochemical formation of polymers containing fullerenes and studies of their properties and applications are critically reviewed. From a structural point of view, these polymers can be divided into four main categories including (1) polymers with fullerenes physically incorporated into the foreign polymeric network without forming covalent bonds, (2) fullerene homopolymers formed via [2+2] cycloaddition, (3) “pearl necklace” polymers with fullerenes mutually linked covalently to form polymer chains, and (4) “charm bracelet” polymers containing pendant fullerene substituents. The methods of electrochemical polymerization of these systems are described and assessed. The structural features and properties of the electrochemically prepared polymers and their chemically synthesized analogs are compared. Polymer films containing fullerenes are electroactive in the negative potential range due to electroreduction of the fullerene moieties. Related films made with fullerenes derivatized with electron-donating moieties as building blocks are electroactive in both the negative and positive potential range. These can be regarded as “double cables” as they exhibit both p- and n-doping properties. Fullerene-based polymers may find numerous applications. For instance, they can be used as charge-storage and energy-converting materials for batteries and photoactive units of photovoltaic cell devices, respectively. They can be also used as substrates for electrochemical sensors and biosensors. Films of the C₆₀/Pt and C₆₀/Pd polymers containing metallic nano-particles of platinum and palladium, respectively, effectively catalyze the hydrogenation of olefins and acetylenes. Laser ablation of electrochemically formed C₆₀/M and C₇₀/M polymer films (M=Pt or Ir) results in fragmentation of the fullerenes leading to the formation of hetero-fullerenes, such as [C₅₉M]⁺ and [C₆₉M]⁺.Dedicated to Professor Dr. Alan M. Bond on the occasion of his 60th birthday.