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Lithium Diisopropylamide-Mediated Ortholithiations: Lithium Chloride Catalysis

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journal contribution
posted on 06.03.2009, 00:00 by Lekha Gupta, Alexander C. Hoepker, Kanwal J. Singh, David B. Collum
Ortholithiations of a range of arenes mediated by lithium diisopropylamide (LDA) in THF at −78 °C reveal substantial accelerations by as little as 0.5 mol % of LiCl (relative to LDA). Substrate dependencies suggest a specific range of reactivity within which the LiCl catalysis is optimal. Standard protocols with unpurified commercial samples of n-butyllithium to prepare LDA or commercially available LDA show marked batch-dependent ratesup to 100-foldthat could prove significant to the unwary practitioner. Other lithium salts elicit more modest accelerations. The mechanism is not discussed.