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Oxo Derivatives (oxo + derivative)
Selected AbstractsMeroterpenoid Pigments from Albatrellus flettii (Basidiomycetes),EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 10 2007Barbara Koch Abstract The pigments responsible for the blue colour of the North American polypore Albatrellus flettii have been isolated and their structures elucidated by spectroscopic methods. Albatrellin, a dimeric meroterpenoid with a furylbenzoquinone chromophore, is accompanied by its 16-hydroxy and 16-oxo derivatives. The latter has recently been described as grifolone B from a Japanese collection of A. caeruleoporus. Based on the idea that albatrellin is formed in nature by oxidative coupling of a grifolinquinone with the furan derivative cristatin, the blue pigment was synthesized in vitro. The reaction could be applied to the synthesis of several analogues.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Complete assignments of 1H and 13C NMR resonances of oleanolic acid, 18,-oleanolic acid, ursolic acid and their 11-oxo derivativesMAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2003Werner Seebacher Abstract Complete assignments of 1H and 13C NMR chemical shifts for oleanolic acid, 18,-oleanolic acid, ursolic acid and their 11-oxo derivatives based on 1H, 13C, 2D DQF-COSY, NOESY, HSQC, HMBC and HSQC-TOCSY experiments were achieved. Copyright © 2003 John Wiley & Sons, Ltd. [source] Reactivity of Molecular Dioxygen towards a Series of Isostructural Dichloroiron(III) Complexes with Tripodal Tetraamine Ligands: General Access to ,-Oxodiiron(III) Complexes and Effect of ,-Fluorination on the Reaction KineticsCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2008Nasser Abstract We have synthesized the mono, di-, and tri-,-fluoro ligands in the tris(2-pyridylmethyl)amine (TPA) series, namely, FTPA, F2TPA and F3TPA, respectively. Fluorination at the ,-position of these nitrogen-containing tripods shifts the oxidation potential of the ligand by 45,70,mV per added fluorine atom. The crystal structures of the dichloroiron(II) complexes with FTPA and F2TPA reveal that the iron center lies in a distorted octahedral geometry comparable to that already found in TPAFeCl2. All spectroscopic data indicate that the geometry is retained in solution. These three isostructural complexes all react with molecular dioxygen to yield stable ,-oxodiiron(III) complexes. Crystal structure analyses are reported for each of these three ,-oxo compounds. With TPA, a symmetrical structure is obtained for a dicationic compound with the tripod coordinated in the ,4N coordination mode. With FTPA, the compound is a neutral ,-oxodiiron(III) complex with a ,3N coordination mode of the ligand. Oxygenation of the F2TPA complex gave a neutral unsymmetrical compound, the structure of which is reminiscent of that already found with the trifluorinated ligand. On reduction, all ,-oxodiiron(III) complexes revert to the starting iron(II) species. The oxygenation reaction parallels the well-known formation of ,-oxo derivatives from dioxygen in the chemistry of porphyrins reported almost three decades ago. The striking feature of the series of iron(II) precursors is the effect of the ligand on the kinetics of oxygenation of the complexes. Whereas the parent complex undergoes 90,% conversion over 40,h, the monofluorinated ligand provides a complex that has fully reacted after 30,h, whereas the reaction time for the complex with the difluorinated ligand is only 10,h. Analysis of the spectroscopic data reveals that formation of the ,-oxo complexes proceeds in two distinct reversible kinetic steps with k1,10,k2. For TPAFeCl2 and FTPAFeCl2 only small variations in the k1 and k2 values are observed. By contrast, F2TPAFeCl2 exhibits k1 and k2 values that are ten times higher. These differences in kinetics are interpreted in the light of structural and electronic effects, especially the Lewis acidity at the metal center. Our results suggest coordination of dioxygen as an initial step in the process leading to formation of ,-oxodiiron(III) compounds, by contrast with an unlikely outer-sphere reduction of dioxygen, which generally occurs at negative potentials. [source] | ||||||||||