Chemistry: A European Journal 2012-09-03

Fluorinated organocatalysts for the enantioselective epoxidation of enals: molecular preorganisation by the fluorine-iminium ion gauche effect.

Eva-Maria Tanzer, Lucie E Zimmer, W Bernd Schweizer, Ryan Gilmour

Index: Chemistry 36th ed., 18 , 11334-11342, (2012)

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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).Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.