Strong main-group Lewis acids such as silylium ions are known to effectively promote heterolytic C(sp3 )-F bond cleavage. However, carrying out the C(sp2 )-F bond transformation of vinylic C-F bonds has remained an unmet challenge. Herein, we describe our development of a new and simple strategy for vinylic C-F bond transformation of α-fluorostyrenes with silyl ketene acetals catalyzed by B(C6 F5 )3 under mild conditions. Our theoretical calculations revealed that a stabilized silylium ion, which is generated from silyl ketene acetals by carboboration, cleaves the C-F bond of α-fluorostyrenes. A comparative study of α-chloro or bromostyrenes demonstrated that our reaction can be applied only to α-fluorostyrenes because the strong silicon-fluorine affinity facilitates an intramolecular interaction of silylium ions with fluorine atom to cleave the C-F bond. A broad range of α-fluorostyrenes as well as a range of silyl ketene acetals underwent this C-F bond transformation.
Keywords: C−C coupling reactions; C−F bond functionalization; alkenes; carboboration reactions; silylium ions.
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