期刊
CHEMISTRY-A EUROPEAN JOURNAL
卷 20, 期 3, 页码 794-800出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.201303586
关键词
aziridination; catalysis; enantioselectivity; fluorine; gauche effect; pre-organisation
资金
- WWU Munster Graduate School of Chemistry
- Deutsche Forschungsgemeinschaft, Germany [DFG EXC 1003]
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 -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 (sigma(C-H)sigma(C-F)*; F-...N+). Consequently, one of the shielding groups on the fluorine-bearing carbon atom is positioned above the -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 -fluoroamino acids. Crystallographic analyses of both the aziridines and their derivatives are disclosed.
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