Cross-Coupling Yields Tertiary Fluorides

By using an asymmetric Negishi cross-coupling strategy, Yufan Liang and Gregory C. Fu of California Institute of Technology have developed a catalytic enantioselective synthesis of acyclic tertiary alkyl fluorides (J. Am. Chem. Soc. 2014, DOI: 10.1021/ja501815p). Motivated by applications in biomedical research and materials science, chemists have been on a tear in recent years creating strategies to increase the diversity of organofluorine compounds. In the case of alkyl fluorides, several research groups have made advances in preparing α-fluoroaldehydes in which a secondary stereogenic carbon-bearing fluorine sits next to a carbonyl group. The Caltech team’s new method uses a nickel bis(oxazoline) catalyst to couple α-bromo-α-fluoroketones with arylzinc reagents to form α-fluoroketones containing a tertiary fluorine-substituted carbon (shown). The researchers varied both the aryl and alkyl groups on the starting fluoroketone and the aryl group on the zinc reagent to come up with an array of tertiary alkyl fluorides in moderate yields and high enantiomeric excesses. Liang and Fu show that the α-fluoroketones can be further derivatized to other families of organofluorine molecules by additions to the carbonyl group and by selective Baeyer-Villiger oxidations to form fluoroesters.