Diverting the 5-<i>exo</i>-Trig Oxypalladation to Formally 6-<i>endo</i>-Trig Fluorocycloetherification Product through 1,2-O/Pd(IV) Dyotropic Rearrangement
Jing Gong, Qian Wang, Jieping Zhu
Abstract
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(sp 3 )–Pd bond by an internal nucleophile that is materialized by the development of a Pd(II)-catalyzed oxidative bis-heterocyclization of alkenes.