Highly stereoselective addition of stannylcuprates to alkynones

The addition of stannylcuprate reagents such as (Bu3Sn)(PhS)CuLi to alkynones has been found to proceed in high yield and with excellent stereoselectivity for the Z isomer of the product (>95%). The behavior of the stannylcuprates is thus very different from that of their "carbocuprate" counterparts such as Me2CuLi or Me2Cu(CN)Li2 which are nonstereoselective. Furthermore, in contrast to the reactions of (R3Sn)(PhS)CuLi with the corresponding alkynoates, the presence of a proton source in the reaction medium has no effect on the stereoselectivity of the reaction of alkynones.     

Diels-alder reaction of 2-chloro-2-nitrosopropane with 1,3-cyclohexadiene

3-(2-Chloropropyl)-2-oxa-3-azabicyclo[2.2.2]oct-5-ene and 2-oxa-3-azabicyclo[2.2.2]oct-5-ene hydrochloride have been prepared by cycloaddition of 2-chloro-2-nitrosopropane to 1,3-cyclohexadiene and their structure determined by nmr, using a ¹H nmr shift reagent.     

The effect of 2,2′-bipyridyl on the stability of Cu(II) complexes with carboxylic acids

The stability constants β₂, and β₂ of simple Cu(II) complexes with methoxyacetic, phenylacetic, and cyclohexylacetic acid were determined spectrophotometrically and compared with the stability of composite complexes containing 2,2′-bipyridyl as the first ligand and the above mentioned acid as the second ligand. In each case the stability of the composite complex Cu(bip)L⁺ was found to exceed that of the simple complex CuL⁺ and the differences in the values of log β are comprised within 0.15–0.17.     

HPLC Method for Determination of Rosiglitazone in Plasma

A fast and sensitive high performance liquid chromatography method for quantitative determination of rosiglitazone in human plasma has been developed. The extraction from plasma was performed using solid-phase extraction (SPE) on C4 silica (100 mg) disposable extraction cartridges (DEC). The separation of rosiglitazone and two metabolites was achieved on a Phenomenex® Synergi 4 µm MAX-RP (150 × 4.6 mm) column, protected by a guard column. The mobile phase was 0.01 M ammonium acetate, pH 7.0 - acetonitrile (65:35, v/v). (3S)-3-OH-quinidine was used as internal standard. The analytes were detected using fluorescence detection. The method was validated. The limit of quantitation was 1 ng mL⁻¹ and the detection limit was 0.25 ng mL⁻¹ for rosiglitazone in human plasma. The recovery was 90% for rosiglitazone. Linearity was observed over a range of 1-1000 ng mL⁻¹ (r²=0.9959). The intra- and inter-day precision (C.V.) did not exceed 8.7 %. Applicability of the method was demonstrated by a clinical pharmacokinetic study. A healthy volunteer received in two separate phases 4 mg and 8 mg rosiglitazone maleate as a single oral dose. Plasma concentrations were measured for 24 h in both phases.     

An intercomparison of sampling techniques for measurements of radiocaesium in upland pasture and soil

An intercomparison of sampling procedures used by five laboratories for the determination of radiocaesium in vegetation and peaty soil was carried out at two locations in Cumbria. The multiple sampling has given information on the homogeneity of the parameters studied at each location. The parameters comprise soil bulk densities, total deposition of¹³⁷Cs, deposition of¹³⁷Cs in three soil layers, biomass densities, concentrations of¹³⁷Cs in pasture, and activity ratios (¹³⁴Cs/¹³⁷Cs) in soil and vegetation. The determination of total deposition of¹³⁷Cs gave no indication of differences between the laboratories. The results from the soil profiles do indicate significant differences between laboratories. One laboratory using a coring technique observed difficulties during sampling due to compression of the soil. The coring technique should thus be avoided or applied with extreme care for the sampling of depth profiles in peaty soil. The results from the sampling of pasture show no indication of differences between the laboratories. For the parameters studied the observed variabilities across soil depths and locations range from 10% to 81% in terms of relative standard deviations. A comparison across all results at the two locations indicate a 50% higher field variability at one of the sites relative to the other.     

The psuedo‐michael reaction of 2‐aminoimidazolines 2. Part 1. Synthesis and structure assignment of isomeric 5(1H)‐Oxo and 7(1H)‐Oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates

The pseudo‐Michael reaction of 1‐aryl‐2‐aminoimidazolines‐2 with diethyl ethoxymethylenemalonate (DEEM) was investigated. Extensive structural studies were performed to confirm the reaction course. For derivatives with N1 aromatic substituents, it was found that the reaction course was temperature dependent. When the reaction temperature was held at ?10 °C only the formation of 1‐aryl‐7(1H)‐oxo‐2,3‐dihydroimi‐dazo[1,2‐a]pyrimidine‐6‐carboxylates ( 4 ) was observed in contrast to earlier suggestions. Under the room temperature conditions, the same reaction yielded mixtures, with varying ratio, of isomeric 1‐aryl‐7(1H)‐oxo‐ ( 4a‐4f ) and 1‐aryl‐5(1H)‐oxo‐2,3‐dihydroimidazo[1,2‐a]pyrimidine‐6‐carboxylates ( 5a‐5f ). The molecular structure of selected isomers, 4b and 5c , was confirmed by X‐ray crystallography. Frontal chro‐matography with delivery from the edge was applied for the separation of the isomeric esters. The isomer ratio of the reaction products depended on the character of the substituents on the phenyl ring. The 1‐aryl‐7(1H)‐oxo‐carboxylates ( 4a‐4f ) were preferably when the phenyl ring contained H, 4‐CH₃, 4‐OCH₃ and 3,4‐Cl₂ substituents. Chloro substitution at either position 3 or 4 in the phenyl ring favored the formation of isomers 5a‐5f . The isomer ratios were confirmed both by ¹H NMR and chromatography. The reaction of the respective hydrobromides of 1‐aryl‐2‐aminoimidazoline‐2 with DEEM, in the presence of triethylamine, gave selectively 5(1H)‐oxo‐esters ( 5a‐5f ).     

UV absorption spectra of HO2, CH3O2, C2H5O2, and CH3C(O)CH2O2 radicals and mechanism of the reactions of F and Cl atoms with CH3C(O)CH3

Pulse radiolysis techniques were used to measure the gas phase UV absorption spectra of the title peroxy radicals over the range 215–340 nm. By scaling to σ(CH₃O₂)_{240 nm} = (4.24 ± 0.27) × 10^?18, the following absorption cross sections were determined: σ(HO₂)_{240 nm} = 1.29 ± 0.16, σ(C₂H₅O₂)_{240 nm} = 4.71 ± 0.45, σ(CH₃C(O)CH₂O₂)_{240 nm} = 2.03 ± 0.22, σ(CH₃C(O)CH₂O₂)_{230 nm} = 2.94 ± 0.29, and σ(CH₃C(O)CH₂O₂)_{310 nm} = 1.31 ± 0.15 (base e, units of 10^?18 cm² molecule^?1). To support the UV measurements, FTIR‐smog chamber techniques were employed to investigate the reaction of F and Cl atoms with acetone. The F atom reaction proceeds via two channels: the major channel (92% ± 3%) gives CH₃C(O)CH₂ radicals and HF, while the minor channel (8% ± 1%) gives CH₃ radicals and CH₃C(O)F. The majority (>97%) of the Cl atom reaction proceeds via H atom abstraction to give CH₃C(O)CH₂ radicals. The results are discussed with respect to the literature data concerning the UV absorption spectra of CH₃C(O)CH₂O₂ and other peroxy radicals. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 283–291, 2002     

Rate constants for the gas-phase reactions of OH radicals and Cl atoms with n-alkyl nitrites at atmospheric pressure and 298 K

Rate constants for the reactions of OH radicals and Cl atoms with CH₃ONO, C₂H₅ONO, n-C₃H₇ONO, n-C₄H₉ONO, and n-C₅H₁₁ONO have been determined at 298 ± 2 K and a total pressure of approximately 1 atm. The OH rate data were obtained using both the absolute rate technique of pulse radiolysis combined with kinetic spectroscopy and a relative rate method involving simultaneous measurement of the loss of the nitrite and the reference compound. The Cl rate constants were measured using the relative rate method. Values of the rate constants in units of 10^?13 cm³ molecule^?1 s^?1 are:

Solvation of Cobalt(II) Ion in N,N-Dimethylformamide–Methanol Mixed Solvent: Calorimetry and VIS Spectroscopy Studies

The enthalpies of solution of Co(II) and Na(I) trifluoromethanesulfonates (triflates) in N,N-dimethylformamide (DMF)–methanol (MeOH) mixtures have been measured over the whole range of solvent composition. From these data the enthalpies of transfer of Co(II) and triflate ions from methanol to the mixed solvent have been determined usingliterature values of the enthalpies of transfer of the Na⁺ ion. The results have been analyzed by means of the theory of preferential solvation. The analysis revealed the preference of DMF for solvating the Co(II) ion in the MeOH-rich region of solvent composition and the lack of preference of any component in the DMF-rich region. Visible absorption spectra of the Co(II) ion in DMF–MeOH mixtures have been also measured in the whole range of solvent composition and analyzed using the partial least-squares method. The mean composition of the solvation sphere of the Co(II) ion versus solvent composition has been determined on the basis of both analyses. The results were found to be consistent with each other and with those obtained previously from FT-IR spectra.     

Untersuchungen über das Gleichgewicht des Hg2+-Hg 2 2+ -Hg-Systems in konzentrierten Perchloratlösungen

The formal potentials of the Hg²⁺/Hg ₂ ²⁺ , Hg ₂ ²⁺ /Hg and Hg²⁺/Hg redox couples and the apparent equilibrium constants of the reaction Hg²⁺ + Hg ∝ Hg ₂ ²⁺ in conc. aqueous solutions of Mg(ClO₄)₂ and Ca(ClO₄)₂ have been determined from emf measurements performed using cells with liquid junction. Based on these data, the hydration numbers of the Hg²⁺ and Hg ₂ ²⁺ ions were estimated.