posted on 2024-03-08, 20:13authored byAlexie
W. Clover, Adam P. Jones, Robert F. Berger, Werner Kaminsky, Gregory. W. O’Neil
Allylsilanes can be regioselectively transformed into
the corresponding
3-silylfluorohydrin in good yield using a sequence of epoxidation
followed by treatment with HF·Et3N with or without
isolation of the intermediate epoxide. Various silicon-substitutions
are tolerated, resulting in a range of 2-fluoro-3-silylpropan-1-ol
products from this method. Whereas other fluorohydrin syntheses by
epoxide opening using HF·Et3N generally require more
forcing conditions (e.g., higher reaction temperature), opening of
allylsilane-derived epoxides with this reagent occurs at room temperature.
We attribute this rate acceleration along with the observed regioselectivity
to a β-silyl effect that stabilizes a proposed cationic intermediate.
The use of enantioenriched epoxides indicates that both SN1- and SN2-type mechanisms may be operable depending on
substitution at silicon. Conformational analysis by NMR and theory
along with a crystal structure obtained by X-ray diffraction points
to a preference for silicon and fluorine to be proximal to one another
in the products, perhaps favored due to electrostatic interactions.