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- Title
Enantioselective Aziridination of Cyclic Enals Facilitated by the Fluorine-Iminium Ion Gauche Effect.
- Authors
Molnár, István Gábor; Tanzer, Eva ‐ Maria; Daniliuc, Constantin; Gilmour, Ryan
- Abstract
The enantioselective, organocatalytic aziridination of small, medium and macro-cyclic enals is reported using ( S)-2-(fluorodiphenyl methyl)-pyrrolidine. Central to the reaction design is the reversible formation of a β-fluoroiminium ion intermediate, which is pre-organised on account of the fluorine-iminium ion gauche effect. This conformational effect positions the fluorine substituent synclinal-endo to the electropositive nitrogen centre thus benefiting from favourable stereoelectronic and electrostatic interactions (σC−H→σC−F*; Fδ−...︁N+). Consequently, one of the shielding groups on the fluorine-bearing carbon atom is positioned above the π-system, forming the basis of an enantioinduction strategy. Treatment of this intermediate with a 'nitrene' source furnished a series of novel, optically active aziridines ( e.r. up to 99.5:0.5). Further derivatisation of the product aziridines gives facile access to various amino acid derivatives, including β-fluoroamino acids. Crystallographic analyses of both the aziridines and their derivatives are disclosed.
- Subjects
AZIRIDINATION; PYRROLIDINE; CHARGE-charge interactions; NITRENES; AZIRIDINES; AMINO acids
- Publication
Chemistry - A European Journal, 2014, Vol 20, Issue 3, p794
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201303586