Transition-Metal-Free Carbofluorination of TBS-Protected Nitrogen-Containing Cyclic Enynols: Synthesis of Fluorinated Azabicycles

The synthesis of fluorinated azabicycles from tert-butyldimethylsilyl-protected N-containing cyclic enynols using inexpensive BF₃·OEt₂ is described. In this reaction, BF₃ reacts as both the Lewis acid and the fluoride source for cyclization/fluorination of the TBS-protected cyclic N-containing enynols. The method provides an easy access to fluorinated azabicycles where a new C­(sp²)–F bond and a new bicyclic skeleton are generated at ambient temperature within 1–13 min under metal-free reaction conditions.