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Synlett 1991; 1991(2): 119-121
DOI: 10.1055/s-1991-20650
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Fluorine- and Trifluoromethyl-Substituted Toluenes: Site Selective Metalation of Aromatic or Benzylic Positions

Sadahito Takagishi* , Manfred Schlosser
  • *Institut de Chimie organique de l'Université, Rue de la Barre 2, CH-1005 Lausanne, Switzerland
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Publication Date:
07 March 2002 (online)

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If employed in tetrahydrofuran and at -75 °C, the superbasic mixture of butyllithium and potassium tert-butoxide metalates 2-, 3- and 4-fluorotoluene exclusively at an aromatic position adjacent to the halogen, as demonstrated by quenching with carbon dioxide to give the corresponding benzoic acids. In contrast, a mixture of lithium diisopropylamide and potassium tert-butoxide selectively deprotonates the benzylic positions of 2- and 3-fluorotoluene to give after quenching with carbon dioxide the corresponding phenylacetic acids. With 3-(trifluoromethyl)-toluene, metal/hydrogen exchange again occurs at the methyl group while the corresponding 2- and 4-isomers do not produce interceptable organometallic intermediates.