Diverting the 5-exo-Trig Oxypalladation to Formally 6-endo-Trig Fluorocycloetherification Product through 1,2-O/Pd(IV) Dyotropic Rearrangement

摘要

Pd-catalyzed cyclizative functionalization of γ-hydroxyalkenes affords tetrahydrofuran derivatives via a key 5-exo-trig oxypalladation step. Herein, we report a palladium­(II)-catalyzed, Selectfluor-mediated formal 6-endo-trig fluorocycloetherification of γ-hydroxyalkenes for the synthesis of functionalized tetrahydropyrans. Mechanistically, an σ-alkyl-Pd­(II) intermediate resulting from the 5-exo-trig oxypalladation process is isolated and characterized by X-ray crystallographic analysis. Its oxidation with Selectfluor to Pd­(IV) triggers the chemoselective 1,2-O/Pd­(IV) dyotropic rearrangement affording, after C–F bond-forming reductive elimination, the tetrahydropyrans with concurrent generation of a tertiary carbon–fluorine bond. The occurrence of this 1,2-positional interchange is further evidenced by trapping the rearranged quaternary C­(sp3)–Pd bond by an internal nucleophile that is materialized by the development of a Pd­(II)-catalyzed oxidative bis-heterocyclization of alkenes.