Enantioselective Fluorination Mediated by Cinchona Alkaloid Derivatives/Selectfluor Combinations: Reaction Scope and Structural Information for <i>N</i>-Fluorocinchona Alkaloids
2001-06-30T00:00:00Z (GMT) by
Cinchona-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 <b>1</b> in up to 91% ee. The first enantioselective syntheses of chiral derivatizing reagents <b>3</b> was accomplished with high ee and in high chemical yields by the DHQDA/Selectfluor combination. 3-Fluorooxindoles <b>7</b> were prepared with ee up to 83% using the (DHQ)<sub>2</sub>AQN/Selectfluor or the (DHQD)<sub>2</sub>PYR/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 <sup>1</sup>H NMR analyses of the cinchona alkaloids/Selectfluor combination have established that the species that mediate this novel reaction are <i>N</i>-fluoroammonium cinchona alkaloid tetrafluoroborates, which adopt open conformations.