Lithium diisopropylamide-mediated ortholithiations: lithium chloride catalysis.
Ortholithiations of a range of arenes mediated by lithium diisopropylamide (LDA) in THF at -78 degrees 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.
Gupta
Lekha
L
Department of Chemistry and Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
Hoepker
Alexander C
AC
Singh
Kanwal J
KJ
Collum
David B
DB
D002384:Catalysis; D018021:Lithium Chloride / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D011437:Propylamines / Q000737:chemistry*
D009942:Organometallic Compounds; D011437:Propylamines; C007442:diisopropylamine; D018021:Lithium Chloride