Mechanism of reduction of benzylidenemalononitrile by 1-benzyl-1,4-dihydronicotinamide

The reduction of benzylidenemdononitrile by 1-benzyl-1,4-dihydronicotinamide undergoes via a one-step hydride transfer mechanism rather than a multistep mechanism involving initial electron transfer.     

Electrochemical reduction of p-nitrosodiphenylamine in, a cationic micellar system

The electroreduction of p-nitrosodiphenylamine (p-NDPA) in an alkaline aqueous solution containing cetyltrimethylammonium bromide (CTAB) as a cationic surfactant was investigated by polarography, cyclic and rotating disc voltammetry. It was found that the reduction of p-NDPA in cationic micellar systems takes place by the ECE mechanism, and, compared to the reduction of the same compound in a homogeneous water solution, has a somewhat lower rate of the overall electrode reaction. The lower reaction rate of p-NDPA reduction in micellar medium is probably due to three main factors: solubilization of p-NDPA in CTAB micelles, adsorption of monomeric surfactant species at the electrode surface and a lower rate of the base catalyzed dehydration reaction (C-step) in the micellar system.     

Production of a poly(pyridinyl radical) by reduction with 1-benzyl-1,4-dihydronicotinamide and N,N′-dicyclohexylalloxan

It was found that 1-ethyl-4-carbomethoxypyridinium iodide could be reduced by 1-benzyl-1,4-dihydronicotinamide (BNAH) and N,N′-dicyclohexylalloxan (DCA) to give 1-ethyl-4-carbomethoxypyridinyl radical. The stable poly(pyridinyl radical) (P-III) was obtained in a similar manner by the reduction of poly(pyridinyl salt) (P-II).     

An efficient palladium(II) based catalytic system for the dimerization of methyl acrylate promoted by silver tetrafluoroborate and p-benzoquinone

Dimerization of methyl acrylate to (E)-Δ²-dimethyl dihydromuconate has been improved by a catalyst containing palladium(II), silver tetrafluoroborate and p-benzoquinone which gave satisfactory turnover numbers (up to 340) and high selectivity (94–96%).     

Heterogeneous ozone oxidation reactions of 1-pentene, cyclopentene, cyclohexene, and a menthenol derivative studied by sum frequency generation

We report vibrational sum frequency generation (SFG) spectra of glass surfaces functionalized with 1-pentene, 2-hexene, cyclopentene, cyclohexene, and a menthenol derivative. The heterogeneous reactions of ozone with hydrocarbons covalently linked to oxide surfaces serve as models for studying heterogeneous oxidation of biogenic terpenes adsorbed to mineral aerosol surfaces commonly found in the troposphere. Vibrational SFG is also used to track the C=C double bond oxidation reactions initiated by ozone in real time and to characterize the surface-bound product species. Combined with contact angle measurements carried out before and after ozonolysis, the kinetic and spectroscopic studies presented here suggest reaction pathways involving vibrationally hot Criegee intermediates that compete with pathways that involve thermalized surface species. Kinetic measurements suggest that the rate limiting step in the heterogeneous C=C double bond oxidation reactions is likely to be the formation of the primary ozonide. From the determination of the reactive uptake coefficients, we find that ozone molecules undergo between 100 and 10000 unsuccessful collisions with C=C double bonds before the reaction occurs. The magnitude of the reactive uptake coefficients for the cyclic and linear olefins studied here does not follow the corresponding gas-phase reactivities but rather correlates with the accessibility of the C=C double bonds at the surface.     

The study of the electrochemical oxidation mechanism of diphenylamine derivatives in dipolar aprotic solvents: II. The electrochemical oxidation of 4-aminodiphenylamine in acetonitrile

The electrochemical oxidation of 4-aminodiphenylamine was investigated in acetonitrile. Voltammetry at a rotating Pt electrode, controlled potential electrolysis and cyclic voltammetry were the techniques followed. The oxidation occurred in two steps, the first involves the complete oxidation of one molecule through an ECE mechanism. The ejected proton—in the follow-up reaction—is received by the other molecule which undergoes oxidation at the potential of the second step. This result was confirmed from the effect of acid and base addition on the oxidation patterns.     

Mechanism of the catalytic oxidation of hydrocarbons by N-hydroxyphthalimide: a theoretical study

The mechanism of the recently proposed catalytic oxidation of hydrocarbons by oxygen in the presence of N-hydroxyphthalimide (NHPI) was established by quantum chemical calculations, consistent with experiments.     

Total synthesis of the novel, biologically active epoxyquinone dimer (+/-)-torreyanic acid: a biomimetic approach

[reaction: see text] A total synthesis of the complex, biologically active, dimeric natural product (+/-)-torreyanic acid, which is composed of seven rings and laced with dense, variegated oxy-functionalization, has been accomplished from readily available allyl-substituted p-benzoquinone 8. Our synthetic stratagem involves crafting an epoxyquinone monomer for use in a biomimetic cascade process involving tandem a 6pi electrocyclization and a Diels-Alder dimerization.     

Use of different microporous and mesoporous materials as catalyst in the Diels–Alder and retro-Diels–Alder reaction between cyclopentadiene and p-benzoquinone: Activity of Al-, Ti- and Sn-doped silica

Diels–Alder cycloaddition between cyclopentadiene and p-benzoquinone has been studied using amorphous silica and different ITQ-2 and MCM-41 pure silica and metal containing materials as catalysts. The reaction can afford different products depending on the molecular reacting site, and the possibility of consecutive additions. Structured solid catalysts increase the selectivity to the endo–endo isomer. Silanol groups have not enough Brönsted acidity to interact with the carbonyl groups present in the dienophile, to reduce LUMO's energy and provide a better overlap between HOMO and LUMO, according to the frontier molecular orbital theory.

The introduction of transition metal atoms in the framework increases the reaction rate for the Diels–Alder reaction while preserving the selectivity to the endo–endo isomer. The presence of more acidic OH groups enhance the retro-Diels–Alder reaction increasing the selectivity to the endo–exo isomer.     

Photodecarboxylative addition of carboxylates to phthalimides: a concise access to biologically active 3-(alkyl and aryl)methylene-1H-isoindolin-1-ones

A series of 3-(alkyl and aryl)methyleneisoindolin-1-one derivatives were synthesized in a simple two-step procedure using a recently established photodecarboxylative addition of carboxylates to phthalimides as the key-step. Subsequent acid-catalyzed dehydration and deprotection furnished the desired target compounds with high E-selectivity. The reaction sequence was applied to the synthesis of the known bioactive phenylethylene derivative, AKS-186. Different analogues, including heteroatom-containing isosteres were also synthesized using this approach.     

Direct electrochemical oxidation of a pesticide, 2,4-dichlorophenoxyacetic acid,at the surface of a graphite felt electrode: Biodegradability improvement

Pesticides’ biorecalcitrance can be related to the presence of a complex aromatic chains or of specific bonds, such as halogenated bonds, which are the most widespread. In order to treat this pollution at its source, namely in the case of highly concentrated solutions, selective processes, such as electrochemical processes, can appear especially relevant to avoid the possible generation of toxic degradation products and to improve biodegradability in view of a subsequent biological mineralization. 2,4-D was found to be electroactive in oxidation, but not in reduction, and the absence of hydroxyl radicals formation during the electrochemical step was demonstrated, showing that the pretreatment can be considered as a “direct” electrochemical process instead of an advanced electrochemical oxidation process. The presence of several degradation products in the oxidized effluent showed that the pretreatment was not as selective as expected. However, the relevance of the proposed combined process was confirmed since the overall mineralization yield was close to 93%.     

Synthetic studies on biologically active natural products by a chemicoenzymatic approach: Enantioselective synthesis of C- and N-nucleosides,showdomycin, 6-azapseudouridine and cordycepin

An efficient synthesis of C- and N-nucleosides has been developed in an enantioselective and stereocontrolled manner starting from Diels-Alder adduct of furan and dimethyl acetylenedicarboxylate by chemicoenzymatic strategy. The symmetric unsaturated dimethyl esters 2 and 3 were almost quantitatively hydrolysed with pig liver esterase to yield half-esters 4 and 5 with reasonably high optical yields. Decarboxylative ozonolysis of the chiral half-esters 4 followed by chemical transformation afforded methyl $\text{L}$-riboside 12, but after the enantiomer conversion (4 to 13 and 5 to 28) the methyl $\text{D}$-riboside (17), ( + )-showdomycin (22), and ( ? )-6-azapseudouridine (27), were obtained from 13, and ( ? )-cordycepin (32) was obtained from 28.     

Synthesis of (1s,5r)-karahana ether and (1s,5r)-karahana lactone,the optically active forms of unique monoterpenes wit

(1$\text{S}$,5$\text{R}$)-(-)-Karahana ether (8,8-dimethyl-2-methylene-6-oxabi-cyclo[ 3.2.1]octane) and (1$\text{S}$,5$\text{R}$)-(-)-karahana lactone (8,8-dimethyl-2-methylene-6-oxabicyclo [3.2.1]octan-7-one) were synthesized from ($\text{S}$)-3-hydroxy-2,2-dimethylcyclo-hexanone. The natural karahana lactone was shown to be almost racemic ($\text{ca}$. 1.3 % e.e.).     

Indirect electrochemical oxidation of N -methyl- n -aminophenol by active oxygen species generated in situ from O2, H2O, and H2O2

Indirect electrochemical oxidation of N-methyl-n-aminophenol by active oxygen species was studied. The active species were in situ generated from O₂, H₂O₂, and H₂O in aqueous solutions with various pH values by using a gas-diffusion cathode in a diaphragmless electrolyzer with anodes made of platinum, lea dioxide, and ruthenium-titanium oxide (RTO). Original Russian Text ? G.V. Kornienko, N.V. Chaenko, V.L. Kornienko, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 8, pp. 1285–1289.     

Mechanism of the oxidation of sulfides by dioxiranes. 1. Intermediacy of a 10-S-4 hypervalent sulfur adduct

Earlier studies established that dimethyldioxirane (1a) reacts with sulfides 2 in two consecutive concerted electrophilic oxygen-transfer steps to give first sulfoxides 3 and then sulfones 4. The same sequential electrophilic oxidation model was assumed for the reaction of sulfides 2 with the strongly electrophilic methyl(trifluoromethyl)dioxirane (1b). In this paper we report on a systematic and general study on the mechanism of the reaction of simple sulfides 2 with DMDO (1a) and TFDO (1b) which provides clear evidence for the involvement of hypervalent sulfur species in the oxidation process. In the oxidation of sulfides 2a-c, diphenyl sulfide (2d), para-substituted aryl methyl sulfides 2e-i, and phenothiazine 2k with 1b, the major product was the corresponding sulfone 4, even when a 10-fold excess of sulfide relative to 1b was used. The sulfone:sulfoxide 4:3 ratio depends among other factors on the dioxirane 1a or 1b used, the sulfide substitution pattern, the polar, protic, or aprotic character of the solvent, and the temperature. The influence of these factors and also deuterium and (18)O tracer experiments performed allow a general mechanism to be depicted for these oxidations in which the key step is the reversible cyclization of a zwitterionic intermediate, 6, to form a hypervalent sulfur species, 7. The classical sequential mechanism which establishes that sulfides are oxidized first to sulfides and then to sulfones can be enclosed in our general picture of the process and represents just those particular cases in which the zwitterionic intermediate 6 decomposes prior to undergoing ring closure to afford the hypervalent sulfurane intermediate 7.     

Identification of the 2-hydroxymethyl-3,4-dihydroxypyrrolidine (or 1,4-dideoxy-1,4-iminopentitol) from angylocalyx boutiqueanus and from arachniodes standishii as the (2R, 3R, 4S)-isomer by the synthesis of its enantiomer.

The {=D}-xylo and {=L}-arabino isomers of 1,4-dideoxy-1,4-iminopentitol have been synthesised from {=L}-arabinose, and the {=L}-arabino isomer was found to be the enantiomer of the alkaloid from $\text{Angylocalyx Boutiqueanus}$. The alkaloid from $\text{Arachniodes Standishii}$, recently reported to have the xylo configuration, was also shown to be the {=D}-arabino isomer.