Synlett 2004(10): 1703-1706  
DOI: 10.1055/s-2004-829571
LETTER
© Georg Thieme Verlag Stuttgart · New York

First Enantio-Flexible Fluorination Reaction Using Metal-Bis(oxazoline) Complexes

Norio Shibata*, Takehisa Ishimaru, Tatsuya Nagai, Junji Kohno, Takeshi Toru*
Department of Applied Chemistry, Graduate School of Engineering, Nagare College, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan
Fax: +81(52)7355442; e-Mail: nozshiba@nitech.ac.jp; e-Mail: toru@nitech.ac.jp;
Further Information

Publication History

Received 23 April 2004
Publication Date:
15 July 2004 (online)

Abstract

The first examples of an elective sense of enantioselectivity in enantioselective fluorination reaction using (S,S)-bis(oxazoline)-Ph complexed with Cu(II) or Ni(II) are described.

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Although we tentatively speculate the geometry of the metal centers as shown in Figure [2] , they can be changed depending on the conditions, counter anions and substrates. Geometry optimizations are under being performed by MO calculations and X-ray crystallographic studies of the intermediates.

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General Procedure: Metal salt (10 mol%) and the (S,S)-bis(oxazoline)-Ph (10 mol%) were stirred under vacuum for 2 h at r.t. Dry solvent (1 mL, and 4 Å molecular sieves) was added under nitrogen atmosphere and stirred for 1 h. Then a solution of substrate 1 (0.10-0.20 mmol) in dry solvent (2 mL) was added to the catalyst solution. After stirring for another 30 min, the reaction vessel was dipped into a temperature-controlled bath as indicated in Table [1] , N-fluorobenzenesulfonimide (1.2 equiv) was added directly to the mixture. The reaction was stirred at the temperature for 1 h to overnight with monitoring by TLC; it was stopped by the addition of H2O (note; when NFSI was added at -10 °C, the resulting mixture was allowed to warm to r.t. overnight). The reaction mixture was then diluted with CH2Cl2, washed with sat. aq Na2CO3 solution and brine, dried over MgSO4 and the solvent was evaporated under reduced pressure. The residue was purified by column chromatography on silica gel eluting with hexane-EtOAc to give the fluorinated product. The ee of the product was determined by chiral HPLC on CHIRALPAK AD-H column.