- Crystal structure of and conformational equilibria in 1,1′-dihydroxybis(4H-cyclopenta[def]phenanthrene) and related derivatives
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The aromatic protons and carbons in the NMR spectra of certain clamped 1,1,2,2-tetraarylethane-1,2-diols undergo intermediate exchange at ambient temperature as the result of conformational equilibrium between two enantiomeric gauche forms. The crystal structures for two of these derivatives show the conformational preference for this geometry in the solid state in contrast to other reported undamped 1,1,2,2-tetraarylethane-1,2-diols. The conformational preference of these vicinal diols parallels that for the 1,1,2,2-tetraarylethanes. However, in the asymmetrically substituted diphenylmethylfluorene series, the vicinal diol prefers to adopt a gauche conformation in contrast to the hydrocarbon which prefers the anti geometry attributed to hydrogen bonding effects in the former. The results of AM1 calculations for the conformational preferences of this series of diols and ethanes are included and agree with experimental observations. Copyright
- Hoang, Mary,Mladenova, Gabriela,Hopkinson, Alan C.,Ramnauth, Jailal,Lee-Ruff, Edward
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p. 294 - 298
(2007/10/03)
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- Synthesis of Ketone and Alcohol Derivatives of Methylene-Bridged Polyarenes, Potentially New Classes of Active Metabolites of Carcinogenic Hydrocarbons
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Methods for the syntheses of bridge ketone and alcohol derivatives of methylene-bridged polyarenes from the parent hydrocarbons are described.The polyarenes investigated include 4H-cyclopentaphenanthrene (1a), fluorene (2a), 7H-benzofluorene (3a), 4H-cyclopentachrysene (4a), 11H-benzaceanthrylene (5a), 10H-indenopyrene (6a), 11H-dibenzoaceanthrylene (7a), 4H-fluorenoanthracene (8a), and 7H-dibenzofluorene (9a).The bridge ketone derivatives are most efficiently synthesized via treatment of the parent hydrocarbons with n-butyllithium and reaction of the resulting anionic intermediate s with molecular oxygen.The direct formation of ketones rather than the expected hydroperoxides from reaction of the bridge anions with O2 presumably involves intra- or intermolecular abstraction of a proton from the benzylic site of the intermediate by the peroxy anion leading to loss of hydroxide ion with formation of a carbonyl group.Yields are generally high except in the cases of 1a and 4a; the former affords as the principal product a dimeric alcohol arising from reaction of the anion of 1a with the corresponding ketone 1b.The related bridge alcohols are readily obtained in yields of 75-95percent by reduction of the crude products from the preceding oxidations with NaBH4.
- Harvey, Ronald G.,Abu-shqara, Elias,Yang, ChengXi
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p. 6313 - 6317
(2007/10/02)
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