Enantioselective fluorination mediated by cinchona alkaloid derivatives/Selectfluor combinations: reaction scope and structural information for N-fluorocinchona alkaloids.
Cinchona-alkaloid/Selectfluor combinations efficiently fluorinate a variety of carbonyl compounds in a highly enantioselective manner to furnish chiral alpha-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.
Shibata
N
N
Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Sugitani 2630, Toyama 930-0194, Japan.
Suzuki
E
E
Asahi
T
T
Shiro
M
M
D002930:Cinchona Alkaloids / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003979:Diazonium Compounds; D015195:Drug Design; D005461:Fluorine / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013237:Stereoisomerism
D002930:Cinchona Alkaloids; D003979:Diazonium Compounds; D007211:Indoles; D005461:Fluorine; C408750:selectfluor