Regiochemical control in intramolecular cyclization of methylene-interrupted epoxydiols

[GRAPHICS] Methylene-interrupted epoxydiols have multiple regiochemical routes for cyc lization. The 5-exo process is the most prevalent under acidic conditions. However, the regioselectivity can be controlled by the appropriate choice o f acid promoter and pendant groups adjacent to the epoxide. The 5-exo produ ct is obtained exclusively without the presence of a carbocation-stabilizin g pendant group. Alkenyl and thiophenyl groups adjacent to the epoxide alte r the regioselectivity and enable access to the 5-endo tetrahydrofuran and 6-endo tetrahydropyran products.