Highly Stereoselective Intramolecular Carbofluorination of Internal -Ynones Promoted by Selectfluor.

Herein, we report a metal-free intramolecular carbofluorination protocol for the synthesis of tetrasubstituted monofluoroalkenes from internal -ynones and Selectfluor with both high stereoselectivity and broad functional group tolerance. The chelation between tetrafluoroborate anion and the oxygen present in the aldehyde group rendered the reaction highly stereoselective, with the tetrafluoroborate serving as the direct fluorine source. Therefore, with addition of sodium tetrafluoroborate, Selectfluor could be reused several times without sacrificing reactivity.