Oxidation leading to reduction: redox-induced electron transfer (RIET)

Complex electron transfer reactions have been characterized whereby in addition to electron transfer, subsequent electrochemical, chemical and even in some cases biological consequences occur. These include a secondary electron transfer that leads to a major rearrangement of the electronic structure, such that an initial oxidation leads to a reduction (or an initial reduction leads to an oxidation) for these valence ambiguous compounds. Mixed valency and valence-tautomeric behaviors can additionally result from these complex electron-transfer-induced reactions.     

Theoretical study of hydrolysis mechanism of khellin

This paper describes khellin hydrolysis mechanism using semiemperical PM3 implemented in Gaussian 03 package. The calculations show that in the presence of an acidic media, an enolate molecular ion leads directly to ω-acetokhellinone while in the basic media it leads to khellinone.     

A theoretical study of the electronic effect of the ligand bite angle on the hydrosilylation reaction of ketones by Cu(I) diphosphine complexes

Diphosphine ligands are commonly used for the catalytic hydrosilylation of ketones using Cu(I) complexes. The electronic effect of the P-Cu-P bite angle has been investigated by a theoretical DFT study. An increase of the P-Cu-P bite angle induces a stronger phosphorus lone pair/Cu-H σ∗ orbital interaction due to a better overlap between these orbitals. This increase in overlap affects structural and electronic properties of the copper hydride catalyst. Increasing the bite angle leads to a decrease of the Cu-P distances and an increases of the Cu-H distances. From an electronic point of view, the effect of an increasing bite angle leads to a weakening of the σ Cu-H orbital, and an increase of the hydride population. The increased polarization of the hydride leads to an easier electron transfer from the σ Cu-H bond to the carbon of the ketone.     

Aromatic substitution via organoboranes 2. Regiospecific alkylation of the furan and pyrrole nucleus

Reaction of 2-lithiofuran or 1-methyl-2-lithiopyrrole with trialkylboranes leads to a borate salt. Subsequent treatment with an appropriate electrophile such as NCS leads to teh 2-alkylfuran or 1-methyl-2-alkylpyrrole.     

The palladium(II)-catalyzed Nazarov reaction

The PdCl(2)-catalyzed cyclization of alpha-alkoxy dienones leads to 2-hydroxycyclopentenones, whereas the Pd(OAc)(2)-catalyzed reaction leads to cross-conjugated cyclopentenones through an oxidative process. [reaction: see text]     

Intestinal glycoproteins of germfree rats. IV. Oligosaccharides obtained by chemical degradation of a water-soluble glycoprotein fraction.

Removal of sialic acid from the glycoprotein and subsequent degradation with sodium hydroxide-sodium borohydride resulted in the formation of a number of low-molecular weight carbohydrate compounds of which three were isolated and characterized: 2-deoxy-2-acetamido-D-galactitol; O-alpha-6-fucopyranosyl (1 leads to 2)-O-Beta-D-galactopyranosyl-(1 leads to 3)-2-deoxy-2-acetamido-D-galactitol (oligosaccharide I); O-Beta-D galactopyranosyl-(1 leads to 3)-2-deoxy-2-acetamido-D-galactitol (oligosaccharide II). From an acetolysate of the desialized glycoprotein a fourth component was obtained and characterized to be O-Beta-D-galactopyranosyl-(1 leads to 4)-2-deoxy-2-acetamido-D-glucose (oligosaccharide III).     

Interrupted Nazarov cyclization on silica gel

Exposure of a mixture of propargyl vinyl ketone and a nucleophilic primary or secondary amine to activated dry silica gel in the absence of solvent leads to a cascade of reactions that results in the formation of an aminocyclopentenone. The reaction with triethylamine leads to a cross-conjugated cyclopentadienone.     

Polarization-transfer methods in solid-state magic-angle-spinning NMR: adiabatic CN pulse sequences.

An adiabatic double-quantum polarization-transfer experiment is described. It can be characterized as an adiabatic variant of the POST-C7 experiment. A continuous variation of the phase increment between pulses leads to the introduction of a fictitious Zeeman field that allows for an adiabatic passage through the recoupling condition. This results in a chemical-shift-offset-compensated adiabatic experiment, which leads to an efficient and broadbanded polarization transfer or to a double-quantum excitation. Similar variations of other C- or R-type experiments can be envisioned.     

Reissert compound studies. XVII. Phosphorus-containing reissert compound analogues

The reaction of isoquinoline, potassium cyamide, and chlorophosphates or chlorothiophosphates leads to the formation of phosphorus containing analogues of Reisert compounds. These analogues can be converted by base to an anion which undergoes elimination to isoquinaldonitrile or which can be alkylated. Acid-catalysed hydrolysis of the analogues leads to isoquinoline.     

Efficient synthesis of tetrasubstituted alkenes by allylsilane-terminated domino-Heck double cyclisation

The domino-Heck double cyclisation of the arylbromides 1, which contain an allylsilane and an alkyne moiety and are easily accessible by an addition of the corresponding lithiated alkynes 5 to the aldehydes 4, leads to the tetrasubstituted alkenes 2 and 3 in good yield. The reaction produces exclusively compounds with an E double bond and additionally proceeds with good to excellent induced diastereoselectivity in the case of 1e and 1f. Irradiation of 2e leads to a steady state equilibrium of the E and Z compounds in a 1:1 ratio.     

Visible-Light-Mediated Heterocycle Functionalization via Geometrically Interrupted [2+2] Cycloaddition

The [2+2] photocycloaddition is the most valuable and intensively investigated photochemical process. Here we demonstrate that irradiation of N-acryloyl heterocycles with blue LED light (440 nm) in the presence of an Ir^III complex leads to efficient and high yielding fused γ-lactam formation across a range of substituted heterocycles. Quantum calculations show that the reaction proceeds via cyclization in the triplet excited state to yield a 1,4-diradical; intersystem crossing leads preferentially to the closed shell singlet zwitterion. This is geometrically restricted from undergoing recombination to yield a cyclobutane by the planarity of the amide substituent. A prototropic shift leads to the observed bicyclic products in what can be viewed as an interrupted [2+2] cycloaddition.     

Selective ATP competitive leads of CDK4: Discovery by 3D-QSAR pharmacophore mapping and molecular docking approach

The discovery of ATP competitive CDK4 inhibitors is an on-going challenging task in cancer therapy. Here, an attempt has been made to develop new leads targeting ATP binding site of CDK4 by applying 3D-QSAR pharmacophore mapping and molecular docking methods The outcome of 6 leads offers a significant contribution for selective CDK4 inhibition, since they show potential binding interactions with Val⁹⁶, Arg¹⁰¹, and Glu¹⁴⁴ residues of CDK4, that are unique and from other kinases. It is worth noting that there is a striking similarity in binding interactions of the leads and known CDK4 inhibitors, namely Abemaciclib, Palbociclib and Ribociclib. Further key features, including high dock score value, good predicted activity, scaffold diversity, and the acceptable ADME profile of leads, provide a great opportunity for the development of highly potent and selective ATP competitive inhibitors of CDK4.     

The reaction of α-methoxyvinyllithium with trialkylboranes

Several alkenyltrialkylborate salts derived from the reaction of α-methoxyvinyllithium (MVL) with trialkylboranes have been prepared. At ?80°C, the initial complex is stable as indicated by its iodination to give moderate yields of enol ethers. Warming the complex to room temperature leads via an alkyl group migration to a new alkenyldialkylmethoxyborate salt. Oxidation of this complex leads to methyl ketones. Alternatively, treatment of this salt with various electrophiles, such as acid, iodine, or alkylating agents prior to oxidation leads to methyldialkylcarbinols, 1,1-dialkylethylenes and hindered tertiary alcohols, respectively. The products can be rationalized by electrophilic attack at the β carbon of an alkenylborate salt. The remarkable nucleophilicity of these salts appears to be comparable to that of enamines.     

Mechanochemical modification of the structure of brown coal humic acids for preparing a sorbent for heavy metals

Mechanochemical modification of the structure of brown coal humic acids with classical base (NaOH) and oxidizing base (Na₂CO₃·1.5H₂O₂) reagents was studied. Treatment of brown coal under these conditions leads to an increase in the degree of recovery of humic acids without breaking the macrostructure of the molecules. The reaction with the base reagent leads to an increase in the content of carboxy groups at hydrocarbon chains, whereas the action of the oxidizing base reagent leads to an increase in the content of phenolic and carboxy groups at aromatic rings, with the formation of chelating structures. The samples obtained show high performance as sorbents for heavy metals.     

New liquid crystalline phases with layerlike organization

Novel lamellar mesophases which are quite distinct from conventional smectic mesophases were obtained with a bolaamphiphilic triblock molecule composed of a rigid biphenyl core, two polar 2,3-dihydroxypropoxy groups in the terminal 4- and 4'-positions, and a semiperfluorinated chain [O(CH2)6C10F21] in the lateral 3-position. The competitive combination of microsegregation and rigidity in this molecule leads to layer structures in which the bolaamphiphilic cores segregate from the lateral chains into distinct sublayers. In these sublayers the biphenyl cores are aligned parallel to the layer planes. Decreasing the temperature leads to a subsequent inset of orientational and positional order of the biphenyl unit, which leads to a transition from an uniaxial SmA phase to a biaxial SmAb phase and finally to a mesophase with an additional periodicity within the aromatic sublayers. Here, microsegregation occurs on two distinct levels: The segregation of the nonpolar chains from the aromatic cores leads to the "bulk" layer structure and segregation of polar and aromatic subunits within the aromatic sublayers gives rise to an additional periodicity within the aromatic sublayers. These phases can be regarded as smectic phases built up by quasi-2D layers with nematic, respectively SmA-like order, separated by isotropic layers of the lateral chains.     

Small-angle light scattering from thin polymer films: Multiple scattering from Debye–Bueche scatterers

An extension of Hartel's theory for multiple scattering has been applied to the case of small-angle light scattering from polymer films with random two-phase morphology. The scattering is treated in terms of Debye–Bueche theory from which values of the correlation length, an average phase size, and mean-square fluctuation in polarizability are determined. It is shown that multiple scattering leads to a reduction in the angular dependence of scattering due to an enhancement of scattering at high angles. This leads to an underestimate of the correlation length and an overestimate of the magnitude of the mean-square polarizability fluctuation.     

A Liouville equation for systems which exchange particles with reservoirs: transport through a nanodevice

A Redfield-like Liouville equation for an open system that couples to one or more leads and exchanges particles with them is derived. The equation is presented for a general case. A case study of time-dependent transport through a single quantum level for varying electrostatic and chemical potentials in the leads is presented. For the case of varying electrostatic potentials the proposed equation yields, for the model study, the results of an exact solution.     

Thermal decay of TEMPO in acidic media via an N-oxoammonium salt intermediate

Disproportionation of TEMPO in acids leads to the formation of an N-oxoammonium salt, which can further decompose under thermal conditions, yielding the corresponding hydroxylamine, N(2)O, CO(2) and a series of dimerisation products. Overall, acid-catalysed thermal decay of TEMPO leads to ca. 80% yield of hydroxylamine.     

Spectral line shape in open-source atomic beam laser spectroscopy experiments

The line shape in atomic beam laser spectroscopy experiments has been calculated for an atomic beam emitted from an open filament and propagated into the vacuum under collisionless conditions. It is shown that the activation energy the atoms have to overcome in order to leave the sample leads to significant deviations from the Voigt line shape. The unreliable application of the Voigt profile under the conditions specified above leads to an overestimate of the line width by up to 70%. A modified Voigt profile is given, which has proved a reliable capability to describe the line shape under the above mentioned conditions.     

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.