Issue Date: June 1, 2009
Directing Fluorination Differently
With the help of a versatile nitrogen-containing moiety, chemists have developed a new reaction for adding fluorine atoms to an aromatic ring. Fluorine atoms abound in pharmaceutical compounds because their love of electrons can elicit molecular effects in the body that can be medically therapeutic. Depending on the desired structure, however, it isn't always easy to add fluorine where it's needed, so chemists are continually seeking new fluorination reactions. Now, Xisheng Wang, Tian-Sheng Mei, and Jin-Quan Yu of Scripps Research Institute have developed a palladium(II)-catalyzed reaction that attaches fluorine ortho to a triflamide directing group on benzylamines (J. Am. Chem. Soc., DOI: 10.1021/ja901352k). Other researchers have used pyridine as a directing group in similar fluorinations, but unlike pyridine, the triflamide can subsequently be converted into other functional groups. The new method can therefore open a pathway to a broad range of fluorinated molecules. The reaction's mechanism isn't yet clear, and the process tends to add an extra fluorine atom to certain substrates. The team is working to refine the selectivity and to extend the reaction to more substrates, Yu says.
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