title: Formation of stable Meisenheimer adduct ion pairs in apolar solvents: implications for stereoselective reactions.
abstract: [reaction: see text] A detailed study concerning the formation of Meisenheimer adducts in biphasic solvent systems is described. The process relies on utilizing a significantly lipophilic quaternary ammonium salt to transfer a nucleophile (e.g., hydroxide ion) between an aqueous and organic layer containing the electron-deficient aromatic substrate. Provided that the organic layer is sufficiently apolar, the resultant Meisenheimer adduct is considerably stable, likely the result of a strong ion-pairing interaction between the large polarizable anionic complex and the diffusively charged tetraalkylammonium cation. Using the diethylamide of 3,5-dinitrobenzoic acid as a model compound, the influence of ion-pairing reagents and solvents on adduct formation was investigated. Dramatically increased equilibrium formation of the Meisenheimer adduct is observed in the biphasic medium (e.g., benzene/2 M NaOH) relative to the same adduct generated in single-phase systems. Spectroscopic studies on this adduct are consistent with those conducted in single-phase polar or dipolar aprotic solvents. The methodology is extended to performing highly enantioselective biphasic kinetic resolutions of several racemic electron-deficient amides.
authors.affiliation: Department of Chemistry, University of Illinois at Urbana Champaign, Urbana, Illinois 61801, USA. sesnyder@mail.med.upenn.edu
authors.forename: Seth E
authors.initials: SE
authors.lastname: Snyder
authors.forename: James R
authors.initials: JR
authors.lastname: Carey
authors.forename: Alex B
authors.initials: AB
authors.lastname: Shvets
authors.forename: William H
authors.initials: WH
authors.lastname: Pirkle