Regioselective Fluorohydrin Synthesis from Allylsilanes

Abstract

Allysilanes 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-substitution is tolerated, resulting in a range of 2-fluoro-3-silylpropan-1ol 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 beta-silyl effect that stabilizes a proposed cationic intermediate. The use of enantioenriched epoxides produces similarly enantioenriched fluorohydrins suggestive of an SN2-type mechanism.

Regioselective Fluorohydrin Synthesis from Allylsilanes and Evidence for a Silicon–Fluorine Gauche Effect

“…As part of an ongoing program investigating new reactions of allylsilanes, − we observed that epoxysilanes, prepared by epoxidation of the corresponding allylsilane, are cleanly converted to the corresponding fluorohydrin upon treatment with triethylamine trihydrofluoride (HF·Et 3 N; Table ). Other HF sources such as Olah’s reagent (HF·Py) resulted in significant decomposition. However, the addition of commercially available HF·Et 3 N (ca.…”