title: Designing fluorinated cinchona alkaloids for enantioselective catalysis: controlling internal rotation by a fluorine-ammonium ion gauche effect (φ(NCCF)).
abstract: The C9 position of cinchona alkaloids functions as a molecular hinge, with internal rotations around the C8-C9 (τ(1)) and C9-C4' (τ(2)) bonds giving rise to four low energy conformers (1; anti-closed, anti-open, syn-closed, and syn-open). By substituting the C9 carbinol centre by a configurationally defined fluorine substituent, a fluorine-ammonium ion gauche effect (σ(C-H) → σ(C-F)*; F(δ-)⋅⋅⋅N(+)) encodes for two out of the four possible conformers (2). This constitutes a partial solution to the long-standing problem of governing internal rotations in cinchonium-based catalysts relying solely on a fluorine conformational effect.
authors.affiliation: Laboratory for Organic Chemistry, Swiss Federal Institute of Technology (ETH) Zürich, 8093 Zürich, Switzerland.
authors.forename: Eva-Maria
authors.initials: EM
authors.lastname: Tanzer
authors.forename: W Bernd
authors.initials: WB
authors.lastname: Schweizer
authors.forename: Marc-Olivier
authors.initials: MO
authors.lastname: Ebert
authors.forename: Ryan
authors.initials: R
authors.lastname: Gilmour