Catalytic Intramolecular Palladium-Ene Reactions. Preliminay Communication

Pd(dba)₂[dba = dibenzylideneacetone]/PPh₃-or Pd(PPh₃)₄-catalyzed cyclizations of acetoxy-dienes 2 → 3 and 10 → 11 gave 1-vinyl-2-methylidene-subsituted cyclopentances and cyclohexanes in high yield, consistent with a palladium-ene/β-elimination mechanism ( D → E → F , Scheme 2). The efficient and highly stereoselective cyclizations 7 → 7 and 8 → 9 illustrate intramolecular allylpalladium insertions into 1,2-dialkyl-, trialkyl-, trialkyl-, and cyclic alkenes followed by elimination of the exocyclic β–H giving 1,2-divinylcyclopentanes. These new olefin insertions proceed faster in AcOH (compared to THF) and occur preferentially cis relative to the Pd ( 13 → 14 → 15 ).     

Tetrastrontium dimanganese copper nonaoxide,Sr4Mn2CuO9

Single crystals of Sr₄Mn_2.09Cu_0.91O₉ have been grown by flux synthesis and the structure, closely related to the hexagonal perovskite 2H, was solved from single‐crystal X‐ray data in space group P321. The structure of Sr₄Mn₂CuO₉ is composed of chains of face‐sharing polyhedra with a sequence of two octahedra and one trigonal prism. The octahedra are filled by Mn atoms and the Cu atoms are randomly distributed at the centres of the square faces of the trigonal prism. A stacking fault is observed within one of the two chains, which can be attributed to a shifting of the chain along the c axis.     

Postcolumn fluorescence as an alternative to evaporative light scattering detection for ceramide analysis with gradient elution in non-aqueous reversed-phase liquid chromatography

Ceramide analysis was developed with gradient elution in non-aqueous reversed-phase liquid chromatography with evaporative light scattering detection (ELSD) or postcolumn fluorescence detection. Fluorescence detection (excitation, 360 nm; emission, 425 nm) after postcolumn formation of mixed assemblies between eluted ceramides and 1,6-diphenyl-1,3,5-hexatriene was developed. In comparison with ELSD, fluorescence detection allows a better detection of the minor species ceramide from ceramide type III (commercial mixture of non-hydroxy fatty acid-sphingosine) and appears to be more sensitive for quantitation of ceramides at low concentrations. The fluorescence response is linear over a wide range of injected amount of ceramide III (expressed as stearoyl-phytosphingosine): 10 ng to 1000 ng. The response of ELSD is non linear but can be linearized in double logarithmic coordinates for calculations over a narrow range, e.g. between 10 to 350 ng ceramide III injected. The lower quantitation limits of these two detectors are similar: 5 ng ceramide III was injected.