The one-pot successive ring expansion reactions of 1-bromo-9-tert-butyldiphenylsilyloxy-4,5,7,8-diepoxynonanes promoted by AgOTf were investigated. The syn-trans-derivative was treated with AgOTf in dry CH 2 Cl 2 to give the cis-fused perhydrotriflyloxypyranopyran as the major product. On the other hand, the corresonding anti-trans-isomer was transformed into the cis-fused perhydrotriflyloxypyranofuran under the same conditions.