Nickeladihydrofuran. Key intermediate for nickel-catalyzed reaction of alkyne and aldehyde

The formation of a nickeladihydrofuran by oxidative cyclization of an alkyne and an aldehyde with nickel(0) has been demonstrated; the transformation of the nickeladihydrofuran into an enone by decomposition, a lactone by carbonylation and an allylic alcohol by treatment with ZnMe(2) suggests that nickeladihydrofuran is an important key intermediate in a variety of catalytic reactions.     

De novo asymmetric synthesis of D- and L-swainsonine

[reaction: see text] The enantioselective syntheses of both enantiomers of the indolizidine natural product swainsonine have been achieved in 13 steps from furan. The indolizidine ring system is installed by a one-pot hydrogenolysis of both an azide and an O-Bn group along with an intramolecular reductive amination reaction. The asymmetry of swainsonine was introduced by Noyori reduction of an acylfuran. This route relies upon an Achmatowicz rearrangement, a diastereoselective palladium-catalyzed glycosylation, Luche reduction, and a dihydroxylation reaction.     

Volatile phase introduction of metallic beta-diketonates in atomic absorption spectrometry: Zinc acetylacetonate

The combined method volatile phase-atomic spectroscopy is an improvement in comparison with the conventional method of liquid sample introduction. The generation of a volatile phase by sublimation from an ethanolic solution of zinc acetylacetonate monohydrate and the obtainment of an analytical signal by AAS is proposed in this paper. The volatile phase is introduced in a silica tube by means of a nitrogen stream as carrier gas. The proposed method gives an improved sensitivity of 6.2 times with respect to the introduction of the same sample in liquid phase and more than 30 times with respect to the introduction of the zinc as chloride in aqueous solution.     

Diffusioosmosis of electrolyte solutions along a charged plane wall

The steady diffusioosmotic flow of an electrolyte solution along a dielectric plane wall caused by an imposed tangential concentration gradient is analytically examined. The plane wall may have either a constant surface potential or a constant surface charge density of an arbitrary quantity. The electric double layer adjacent to the charged wall may have an arbitrary thickness, and its electrostatic potential distribution is determined by the Poisson-Boltzmann equation. The macroscopic electric field along the tangential direction induced by the imposed electrolyte concentration gradient is obtained as a function of the lateral position. A closed-form formula for the fluid velocity profile is derived as the solution of a modified Navier-Stokes equation. The direction of the diffusioosmotic flow relative to the concentration gradient is determined by the combination of the zeta potential of the wall and the properties of the electrolyte solution. For a given concentration gradient of an electrolyte along a plane wall, the magnitude of fluid velocity at a position in general increases with an increase in its electrokinetic distance from the wall, but there are exceptions. The effect of the lateral distribution of the induced tangential electric field in the double layer on the diffusioosmotic flow is found to be very significant and cannot be ignored.     

Curtius rearrangement of aromatic carboxylic acids to access protected anilines and aromatic ureas

The reaction of a chloroformate or di-tert-butyl dicarbonate and sodium azide with an aromatic carboxylic acid produces the corresponding acyl azide, presumably through the formation of an azidoformate. The acyl azide undergoes a Curtius rearrangement to form an isocyanate derivative which is trapped either by an alkoxide or by an amine to form the aromatic carbamate or urea. The reaction conditions are compatible with a variety of functional groups and allow the synthesis of a number of aniline derivatives containing alkyl, halide, nitro, ketone, ether, and thioether substituents. [reaction: see text]     

Multicomponent and one-pot synthesis of trisubstituted pyridines through a Pd-catalyzed cross-coupling/cross-coupling/cycloaddition sequence

Trisubstituted pyridines are regioselectively synthesized through multicomponent and one-pot processes promoted by a bifunctional Pd-catalyst. The process involves formation of an enamine by Pd-catalyzed amination of an alkenyl bromide, formation of a 2-aza-1,3-butadiene by Pd-catalyzed cross-coupling of a trimethylsilylimine with an alkenyl bromide, and Lewis acid catalyzed cycloaddition between the enamine and the azadiene.     

Reactive crystals. IV. Crystalline state photopolymerization of 5,5′-1,4-phenylene-bis(2-cyano-2,4-pentadienoic acid) derivatives

5,5′-1,4-Phenylene-bis(2-cyano-2,4-pentadienoic acid) derivatives were prepared. Many of this series of compounds were found to be polymerizable in the crystalline state by irradiation with light of wavelength λ > 340 nm. The polymers obtained contain a benzene and a cyclobutane ring in the main chain and have a cyanoacrylate as the side chain. They are crystalline and some of them are soluble in organic solvents. Photopolymerization was found to follow a stepwise mechanism. The polymerization process is separable into an oligomerization and a subsequent polymerization by controlling the wavelength of the irradiating light; an oligomer was obtained by an irradiating light; an oligomer was obtained by an irradiating light of wavelength λ > 430 nm.     

Pillaring effects in macroporous carrageenan-silica composite microspheres

The impregnation of a carrageenan gel by a silica sol is an efficient method to form a composite material which can be conveniently activated by CO2 supercritical drying. The textural properties of the solids have been characterized by nitrogen adsorption-desorption at 77 K and their composition by thermogravimetric analysis and EDX microprobe. Morphology was examined by SEM. The silica-carrageenan composites present an open macroporous structure. Silica particles retained inside the gel behaved as pillars between the polysaccharide fibrils and form a stick-and-ball network. The stiffening of the carrageenan gel by silica prevented its shrinkage upon drying. The nature of the alkali cations affected the retention of silica particles inside the gel. In the absence of silica, carrageenan fibrils rearrange under supercritical drying and form an aerogel with cavities in the mesopore range.     

Electron charge redistribution following electrophilic attack on heterocycles: nitrogen as a charge transducer

It is shown that an electrophilic attack on the ring nitrogen in pyrrole or tryptamine produces an electron charge redistribution that is qualitatively different from the redistribution caused by an attack on the oxygen in furan. The electrophilic attacks are represented theoretically as interactions with a positive point charge and calculated by an ab-initio LCAO-SCF method with gaussian basis sets. Results show that an attacked nitrogen responds to the perturbation by moving electronic charge to the adjacent carbons whereas oxygen retains most of the charge polarized by the interaction. The nitrogen also acts as a charge transducer in other systems that are structurally very different. As a consequence of the charge redistribution, the comparative susceptibility of various sites in the heterocyclic molecules to an electrophilic attack may also depend on the response of the molecule to a prior attack on the heteroatom. The results indicate the need for dynamical reactivity considerations which reflect the variability in the molecular response to an incipient attack and the possibility that enhanced reactivity can be induced at certain sites by this response.     

Is the mechanism of the proline-catalyzed enantioselective aldol reaction related to biochemical processes ?

The enantioselectivity shown by the title reaction is explained by an intramolecular hydrogen bond in an enamine intermediate resulting from nucleophilic catalysis by one molecule of proline and by a proton transfer mediated by a second molecule of proline.     

Stereoselective synthesis of a potent thrombin inhibitor by a novel P2-P3 lactone ring opening

The concise synthesis of a potent thrombin inhibitor was accomplished by a mild lactone aminolysis between an orthogonally protected bis-benzylic amine and a diastereomerically pure lactone. The lactone was synthesized by the condensation of l-proline methyl ester with an enantiomerically pure hydroxy acid, which in turn was synthesized by a highly stereoselective (>500:1 er) and productive (100,000:1, S/C) enzymatic reduction of an alpha-ketoester. In addition, a second route to the enantiomerically pure lactone was accomplished by a diastereoselective ketoamide reduction.     

Total synthesis of N-methylwelwitindolinone D isonitrile

Described is a concise total synthesis of N-methylwelwitindolinone D isonitrile, the first in a family of complex bicyclo[4.3.1]decane-containing indole alkaloids to yield to synthesis. The complete carbon core of the natural product was assembled rapidly through a Lewis acid-mediated alkylative coupling followed directly by a palladium-catalyzed enolate arylation reaction. The final ring of the pentacycle was introduced by an indole oxidation/cyclization, and the isonitrile was installed through the rearrangement of an aldehyde to an isothiocyanate followed by desulfurization.     

Forces between a hard surface and an air–aqueous interface with and without films

The adsorption of particles to air–aqueous interfaces is vital in many applications, such as mineral flotation and the stabilization of food foams. The forces in the system determine whether a particle will attach to an air–aqueous interface. The forces between a particle and an air–aqueous interface are influenced by Derjaguin–Landau–Verwey–Overbeek forces (i.e. van der Waals and electrostatic forces), non–Derjaguin–Landau–Verwey–Overbeek forces (e.g. hydrophobic, hydrodynamic, structural, and capillary forces), liquid drainage, and liquid flow. As an air–aqueous interface can be deformed by a particle, the forces measured between an air–aqueous interface and a particle can differ from those measured between two hard surfaces separated by liquid. The presence of a film at an air–aqueous interface can also change the forces.     

Plasma Induced Degradation of Azobenzene in Water

The degradation of azobenzene (AO) by a gaseous plasma is reported. The plasma was generated in a localized zone between an electrolytic solution and a tip of an anode in contact with the surface of solution by means of contact glow discharge electrolysis. There is an optimum pH for the degradation of AO. Iron (II) had a remarkable catalytic action on it. Furthermore, the degradation followed the first‐order kinetic law. Some of the intermediate products of the degradation process were detected by HPLC.     

Dewetting of thin liquid films near soft elastomeric layers

Thin liquid film instabilities driven by van der Waals forces and in the proximity of soft elastomeric layers are considered in this work through two model problems: (i) a liquid film resting on an elastomeric layer and (ii) a liquid film bounded from one side by a rigid substrate and from the other side by an elastomeric layer. The elastomeric layers are modeled as linear viscoelastic solids, van der Waals forces are assumed to act only in the liquid, and lubrication theory and linear stability analysis are applied. For a liquid film resting on an elastomeric layer, substrate deformability has a destabilizing effect, as evidenced by an increase in the maximum growth rate and range of unstable wavenumbers. The destabilization worsens for thicker solid layers and is due to a lowering of the effective liquid-air interfacial tension. For an elastomeric layer resting on a liquid film, layer deformability has a stabilizing effect for thin layers but a destabilizing effect for thicker layers, with the former due to an enhancement and the latter due to a reduction of the effective solid-air interfacial tension. The results presented here suggest the possibility of exploiting the dewetting of thin liquid films to create topographically patterned surfaces on soft polymeric solids.     

Alkali base-initiated Michael addition/alkyne carbocyclization cascades

A new cascade reaction involving an intramolecular Michael addition followed by an alkyne carbocyclization is presented. The reaction is promoted by a substoichiometric amount of KHMDS and represents one of the rare examples where the carbocyclization of an unactivated alkyne is mediated by an alkali metal base, under mild conditions. The reaction allows the generation of functionally dense, stereochemically defined, tricyclic structures possessing three adjacent stereocenters in good yields and with high stereoselectivity.     

Elektronenübergänge und die Veränderung des Informationsgehaltes chemischer Elemente

The excited valence states of the atom have a decreased spininformation content and an increased quantity of information on electron distribution over atomic orbitals. As a rule, light emission is accompanied by a decrease, light absorption by an increase in the atomic information content. The pairs of atomic (as well as molecular) states with an equal, positive and negative, absolute temperature are characterized by equal information content.

     

Total synthesis of (+/-)-stemodinone via an efficient ring-exchange strategy

A total synthesis of (+/-)-stemodinone, a tetracyclic stemodane diterpene, from the known tricyclic methyl olefin 11 is described. The key steps involve an efficient ring-exchange reaction and palladium(0)-catalyzed lactone migration. The ring-exchange strategy for controlling the stereochemistry was based on an initial Diels-Alder reaction to form a new ring followed by cleavage of the original ring. Cleavage of the original ring of the Diels-Alder adduct 9 was achieved by an initial regio- and chemoselective Baeyer-Villiger oxidation followed by the Pd(0)-catalyzed lactone-migration reaction reported by us.     

Stereocontrolled syntheses of carbocyclic C-nucleosides and related compounds.

Carbocyclic 9-deazapurine nucleosides (1-4), a spiranic pyrimidone carbocyclic compound (5), and an unusual carbocyclic isonucleoside (6) were prepared as enantiomerically pure compounds via the key intermediates 10 and 21 from 1,4-gamma-ribonolactone. The key intermediate 10 was prepared by stereoselective reduction with Bu3SnH and then converted to carbocyclic C-ribonucleosides 1, 3, and 4. 2',3'-Didehydro-2',3'-dideoxycarbocyclic 9-deazainosine (2) was prepared from a 2',3'-dimesylate 17 by treatment with Li2Te followed by an acidic deprotection. The key bicyclic intermediate 21 was prepared from a diol 20 by an intramolecular cyclization using CHI3-Ph3P-imidazole and converted to the spiranic compound 5 and an olefinic nucleoside 6 by the construction of the heterocyclic moiety followed by deprotection.     

Researches on pyridodiazepines. Behavior of 7,8,9,10-tetrahydro-5-methylcyclopenta[e]pyrido[3,2-b][1,4]-diazepin-6(5H)-one with chloroacetyl chloride

Following a previous experiment, an original heteropolycyclic structure 4 was obtained by a reaction of chloroacetyl chloride with compound 3 bearing a conjugated double bond system. The condensation develops with an initial NH-chloroacetylation and ring closure by quaternarization of the pyridine nitrogen. This is achieved through an 1,4 -cycloaddition of chloroketene to make a pyranone ring.