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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.