The formation of lithio derivatives from fluorinated benzenes and fluorinated bromobenzenes has been studied. The bases used were lithium diisopropylamide (LDA) in THF-hexane, butyllithium in diethyl etherhexane and butyllithium in THF-hexane. The lithiated intermediates have been trapped using acetone, to form fluorinated 2-arylpropan-2-ols, or have been warmed to produce benzynes which have been trapped by furan in Diels-Alder additions. The use of LDA allows clean removal of the most acidic proton in the aromatic ring: butyllithium in ether-hexane kings about clean bromine-lithium exchange. In contrast, the use of butyllithium in THF-hexane at -78 "C results in autometallation and the formation of more complex product mixtures. For the formation of the benzynes involved in the Diels-Alder reactions it is necessary to warm the reaction mixtures. When ether-hexane is used as solvent the reactions remain fairly clean, but when THF is added the increasing autometallation again results in more complex reaction mixtures.
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