title: Fluorinated organocatalysts for the enantioselective epoxidation of enals: molecular preorganisation by the fluorine-iminium ion gauche effect.
abstract: The fluorine-iminium ion gauche effect is triggered upon union of a secondary β-fluoroamine and an α,β-unsaturated aldehyde, providing a useful strategy for controlling the molecular topology of intermediates that are central to organocatalytic processes. The β-fluoroamine (S)-2-(fluorodiphenylmethyl)pyrrolidine (1) is an effective catalyst for the enantioselective epoxidation of α,β-unsaturated aldehydes. A process of structural editing has revealed that the efficiency of this catalyst is due to the (fluorodiphenyl)methyl group when it is embedded in a β-fluoroiminium motif. Epoxidations of challenging cyclic α,β-disubstituted, β,β-disubstituted and α,β,β-trisubstituted enals catalysed by 1 proceed with excellent levels of enantiocontrol (up to 98% ee).
authors: Laboratory for Organic Chemistry, Swiss Federal Institute of Technology Zürich, 8093 Zürich, Switzerland.
authors: Eva-Maria
authors: EM
authors: Tanzer
authors: Lucie E
authors: LE
authors: Zimmer
authors: W Bernd
authors: WB
authors: Schweizer
authors: Ryan
authors: R
authors: Gilmour