The synthesis of mono- and diacetyl-9H-fluorenes. Reactivity and selectivity in the Lewis acid catalyzed Friedel-Crafts acetylation of 9H-fluorene

Salam J.J. Titinchi, Fadhil S. Kamounah, Hanna S. Abbo, Ole Hammerich

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    Abstract

    Friedel-Crafts acetylation of 9H-fluorene is an effective route for the preparation of mono- and diacetyl-9H-fluorenes. Using acetylchloride as the reagent and aluminum chloride as the Lewis acid catalyst the effect of the solvent polarity, the temperature, the reaction time and the mode of addition (Perrier or Bouveault) on the reactivity-selectivity pattern was investigated. The results showed that monoacetylation of 9H-fluorene in chloroalkanes and nitromethane gives mixtures of 2-acetyl- and 4-acetyl-9H-fluorene with the former dominating. In addition to these two isomers, 2,7-diacetyl-9H-fluorene was obtained in 5-11 % yield when carbon disulfide was used as the solvent. Acetylation of 9H-fluorene in dichloroethane and carbon disulfide, using an excess of acetyl chloride and aluminum chloride at reflux temperature, gives 2,7-diacetyl-9H-fluorene exclusively in high yields (> 97%). Attempts to carry out diacetylation in nitromethane on the other hand resulted in the formation of monoacetyl derivatives only. The ketones obtained were isolated and identified by various physico-chemical techniques. The 1H NMR spectrum of 4-acetyl-9H-fluorene is reported for the first time. Values of the total energies and the Gibbs free energies at 298K for 9H-fluorene, the five isomeric monoacetyl-9H-fluorenes and the four σ-complexes leading to 1-, 2-, 3- and 4-acetyl-9H-fluorene, respectively, were computed at the DFT B3LYP 6-31G** level of theory. The data serve as a basis for the discussion of the reactivity-selectivity pattern observed and it is concluded that the distribution of products is partly kinetically controlled
    Original languageEnglish
    JournalA R K I V O C
    Volume13
    Pages (from-to)91-105
    ISSN1551-7004
    Publication statusPublished - 2008

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