Journal of the American Chemical Society 2006-12-06

Lithium diisopropylamide solvated by hexamethylphosphoramide: substrate-dependent mechanisms for dehydrobrominations.

Yun Ma, Antonio Ramirez, Kanwal Jit Singh, Ivan Keresztes, David B Collum

Index: J. Am. Chem. Soc. 128(48) , 15399-404, (2006)

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Abstract

Lithium diisopropylamide-mediated dehydrobrominations of exo-2-bromonorbornane, 1-bromocyclooctene, and cis-4-bromo-tert-butylcyclohexane were studied in THF solutions and THF solutions with added hexamethylphosphoramide (HMPA). Rate studies reveal a diverse array of mechanisms based on mono-, di-, and trisolvated monomers as well as triple ions. The results are contrasted with analogous eliminations in THF in the absence of HMPA.