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Enantioselective Fluorination Mediated by Cinchona Alkaloid Derivatives/Selectfluor Combinations: Reaction Scope and Structural Information for N-Fluorocinchona Alkaloids
journal contribution
posted on 2001-06-30, 00:00 authored by Norio Shibata, Emiko Suzuki, Toru Asahi, Motoo ShiroCinchona-alkaloid/Selectfluor combinations efficiently fluorinate a variety of carbonyl compounds
in a highly enantioselective manner to furnish chiral α-fluorocarbonyl compounds. The DHQB/Selectfluor
combination is effective for the enantioselective fluorination of indanones and tetralones 1 in up to 91% ee.
The first enantioselective syntheses of chiral derivatizing reagents 3 was accomplished with high ee and in
high chemical yields by the DHQDA/Selectfluor combination. 3-Fluorooxindoles 7 were prepared with ee up
to 83% using the (DHQ)2AQN/Selectfluor or the (DHQD)2PYR/Selectfluor combination. Since the combinations
are conveniently prepared in situ from readily available reagents, the present system represents a practical
method for enantioselective fluorination. X-ray crystallography and 1H NMR analyses of the cinchona alkaloids/Selectfluor combination have established that the species that mediate this novel reaction are N-fluoroammonium
cinchona alkaloid tetrafluoroborates, which adopt open conformations.