Sigmatropic Dearomatization/Defluorination Strategy for C-F Transformation: Synthesis of Fluorinated Benzofurans from Polyfluorophenols.

Facile synthesis of fluorinated benzofurans from polyfluorophenols has been accomplished by means of a sigmatropic dearomatization/defluorination strategy composed of three processes: (1) interrupted Pummerer reaction of ketene dithioacetal monoxides with polyfluorophenols followed by [3,3] sigmatropic rearrangement, (2) Zn-mediated smooth reductive removal of fluoride from the dearomatized intermediate, and (3) acid-promoted cyclization/aromatization. Mechanistic investigations revealed important characteristic reactivity of polyfluorophenols in the present system. Some of the fluorinated benzofuran products were transformed by utilizing the 2-methylsulfanyl moieties.