From the results shown in this review it can be concluded that the arene-catalysed lithiation of different substrates (non-halogenated precursors, functionalised chlorinated materials, saturated heterocycles and polychlorinated compounds) is a powerful methodology for preparation of a wide range of very reactive or unstable organolithium intermediates, which are versatile species in synthetic organic chemistry. A question remains to be answered: why is the catalytic version more effective than the stoichiometric one? A possible explanation could be that in the presence of a deficiency of the arene, the excess of lithium provokes the formation, at least to some extent, of the corresponding arene-dianion (from the initially formed arene-radical anion). This dianionic species is very powerful as a reduction (lithiation) agent. For this reason, most of the reactions described in this review do not work with a lithium-arene mixture (stoichiometric ratio) under the reaction conditions described here; on the other hand, when the process was successful in the stoichiometric version, yields were lower and reaction times were significantly longer. In addition, combining an arene-catalysed lithiation with Barbier-type reaction conditions (performing the reaction in the presence of the electrophile) the method is very effective in some cases, mainly when polychlorinated compounds are used as synthons for polylithium intermediates.
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