Rearrangement of 2-azanorbornenes to tetrahydrocyclopenta[c]pyridines under the action of activated alkynes – A short pathway for construction of the altemicidin core

A simple approach to a series of 2,4a,7,7a-tetrahydro-1H-cyclopenta[c]pyridines was proposed on the basis of the amino-Claisen rearrangement of readily accessible 2-azabicyclo[2.2.1]hept-5-enes under the action of dialkyl acetylenedicarboxylates, methyl propiolate or propiolamide. The rearrangement is highly diastereoselective and leads to the formation of only one isomer with cis-annulation of the five- and six-membered rings in satisfactory yields. Using the developed method, close analogs of the altemicidin and SB-203207 cores were synthesized.     

Determination of gadolinium in river water by SPE preconcentration and ICP-MS

An analytical scheme was developed for the determination of Gd-diethylenetriaminepentaacetate (Gd-DTPA), Gd and the other rare earth elements (REE) in river water by inductively coupled plasma (quadrupole) mass spectrometry (ICP-Q-MS). The preconcentration step was essential, since the limits of detection of this multielemental analytical technique are higher than the trace concentrations of the interesting elements in river water.Solid phase extraction (SPE) with different commercially available complexing agents (Chelex 100, Toyopearl and ethylhexylphosphates) was employed for the preconcentration of REE. The investigations revealed that complex stability (varying in dependence of the pH value) has a strong influence on the degree of the enrichment of Gd-DTPA. Based on acidified water samples (pH<3) a procedure using ethylhexylphosphates was proposed for the preconcentration of Gd and REE from surface water samples. For this purpose C₁₈-cartridges loaded with ethylhexylphosphates were used, resulting in an enrichment factor of 40.     

Effects of well-defined magnetic field gradients on the electrodeposition of copper and bismuth

Paramagnetic Cu²⁺-ions have been electrodeposited under application of magnetic field gradients. Obtained deposits show a direct correlation of the distribution of magnetic flux density B at the electrode and the deposit thickness and morphology. In contrast to that no influence on the deposit structure has been observed for deposition of Bi from electrolytes containing diamagnetic Bi³⁺-ions. This indicates that the structuring effect is mainly based on the action of the magnetic gradient force. A structuring-mechanism has been proposed that also discusses influences of the Lorentz force.     

Ca3Pt(4+x)Ge(13-y) and Yb3Pt4Ge13: new derivatives of the Pr3Rh4Sn13 structure type

The new phases Ca(3)Pt(4+x)Ge(13-y) (x = 0.1; y = 0.4; space group I2(1)3; a = 18.0578(1) ?; R(I) = 0.063; R(P) = 0.083) and Yb(3)Pt(4)Ge(13) (space group P4(2)cm; a = 12.7479(1) ?; c = 9.0009(1) ?; R(I) = 0.061, R(P) = 0.117) are obtained by high-pressure, high-temperature synthesis and crystallize in new distortion variants of the Pr(3)Rh(4)Sn(13) type. Yb(3)Pt(4)Ge(13) features Yb in a temperature-independent non-magnetic 4f(14) (Yb(2+)) configuration validated by X-ray absorption spectra and resonant inelastic X-ray scattering data. Ca(3)Pt(4+x)Ge(13-y) is diamagnetic (χ(0) = -5.05 × 10(-6) emu mol(-1)). The Sommerfeld coefficient γ = 4.4 mJ mol(-1) K(-2) for Ca(3)Pt(4+x)Ge(13-y), indicates metallic properties with a low density of states at the Fermi level in good agreement with electronic structure calculation (N(E(F)) = 3.3 eV(-1)/f.u.)); the Debye temperature (θ(D)) is 398 K.     

An in situ approach for nickel-catalyzed cycloaddition

A convenient method for preparing pyridines from air-stable, commercially available catalyst precursors is described. The addition of n-BuLi to Ni(acac)2 and an NHC salt (such as IPr.HCl or SIPr.HCl) rapidly generates an active Ni0/NHC catalyst for the cycloaddition of diynes and nitriles that affords pyridines without a decrease in observed yields. The in situ method also converts diynes and carbon dioxide to the corresponding pyrones.     

A comparison of hydrogen bonding solvent effects on the singlet oxygen reactions of allyl and vinyl sulfides, sulfoxides, and sulfones

The singlet oxygen (¹Δ_g) photooxidations of 2-methyl-3-phenylthio-2-butene (1a), 1-[(4-nitrophenyl)thio]-2,3-dimethyl-2-butene (2c), 2-methyl-3-phenylsulfinyl-2-butene (3), 2-methyl-3-phenylsulfonyl-2-butene (6), and 1-[(4-nitrophenyl)sulfonyl]-2,3-dimethyl-2-butene (7c) were conducted in the following deuterated solvents: acetonitrile, benzene, chloroform, methanol, or methanol/water mixture. In each case the ene allylic hydroperoxide products and/or the [2+2] cycloaddition products were quantified and inspected for possible hydrogen bonding induced differences in product selectivity and regiochemistry. After comparison to literature values for related substrates, the results indicate that only photooxidations of vinyl sulfides are susceptible to hydrogen bonding solvent effects.     

Inter-molecular migration during collisional activation monitored by hydrogen/deuterium exchange FT-ICR tandem mass spectrometry

The difficulty with integrating solution-phase hydrogen/deuterium exchange (HDX) and tandem mass spectrometry is that the energy added to cause fragmentation might promote gas-phase migration of the added deuterium atoms. Here, we compare the solution-phase HDX profiles generated from a- b- and y-type fragment ion series originating from capillary-skimmer dissociation. The isotopic distributions of fragments from the different fragment ion types were used to determine the isotopic state of the amide hydrogen within a specific residue. Even though the same amide hydrogen was examined, the result was different for different fragment ion types. This observation indicates that different fragment series are not equally subjected to inter-molecular migration during collision-induced dissociation (CID). We also investigated the gas-phase reactivity of originally undeuterated CID fragments of penta-phenylalanine using gas-phase HDX in an external accumulation hexapole. The incorporation of deuterium into the different fragments was studied as a function of hexapole pressure. It was found that different b- and y-ions from the same peptide had different gas-phase reactivity. However, the a-ions did not display significant gas-phase reactivity. The observed behavior has significant impact on any method that involves comparing the isotopic distributions of different fragment ions. Great care has to be taken in the interpretation of the HDX data using CID to increase the spatial resolution. The isotopic state observed after solution-phase exchange might be more preserved for some CID-fragment types.     

Problems in the IR measuring the acidity of zeolite bridging hydroxyls by low-temperature CO adsorption

Two infrared OH stretching bands are produced after interaction of CO with H-ZSM-5 bridging hydroxyls. These two bands are not due to heterogeneity of the acid sites but arise from Fermi-resonance.