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Contribution à l'étude mécanistique de la métallation à distance. Mise en évidence de la formation intermédiaire d'un gem-dialcoolate dimétallique (Li ou K), premier groupement ortho-directeur doublement chargé

Abstract : Abstract The Directed Ortho-Lithiation and the Directed Remote Metalation are the most effective methods for synthesizing polysubstituted aromatic compounds. Previous results from our group showed that the carboxylic acid group is an effective director of ortho-lithation in benzenoid systems. The reaction does not require the protection and the deprotection of the carboxylic acid group. The present work complements and extends previous research on the mechanism of directed remote-metalations that are followed by intramolecular trapping. The mechanism of the metalation of 2-biphenyl carboxylic acid with n-butyllithium/t-BuOK (1:1 ratio) was determined by deuteriolysis. The deprotonation is not site selective and the base attacks both the ortho (C3) and remote (C2') positions. The resulting metalated species are in equilibrium, and the organometallic resulting from the remote metalation cyclises instantaneously and irreversibly to give a geminal dimetallo dialkoxide group C(OM)2, shifting the equilibrium, by Le Châtelier's Principle. Under suitable conditions, the doubly charged geminal dimetallo dialkoxide group C(OM)2 directs metalation in the adjacent position (C1) affording a stable 1-metallo-9H-fluorene-9,9-dimetallo dialkoxide that can be trapped as such by electrophiles to give 1-substituted 9H-fluoren-9-ones after acidic workup. It is next shown that these results can be extended to the remote metalations of biarylamides, phenothiazines and aminobiphenyls. To the best of our knowledge, the geminal dialkoxide C(OM)2 (M = Li, K) is the first doubly charged director of ortho-metalation. Regiospecific metalations of 3- and 4-biphenylcarboxylic acids and 1-naphtoic acid are also reported. Key words: Directed remote Metalation, regioselectivemetalation, optional site selectivity Benzoic acid, fluoren-9-one, biphenylcarboxylic acid Alkyllithiums, lithium amides, LiCKOR, CIPE effect
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Submitted on : Wednesday, March 23, 2005 - 5:56:19 AM
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David Tilly. Contribution à l'étude mécanistique de la métallation à distance. Mise en évidence de la formation intermédiaire d'un gem-dialcoolate dimétallique (Li ou K), premier groupement ortho-directeur doublement chargé. Autre. Université du Maine, 2004. Français. ⟨tel-00008848⟩

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