Heterogeneous acid-catalyzed (2,5) oxonium-ene reaction for eight-membered ring formation

The (2,5) ene cyclization of cyclic allylic lactol ether 1 as a substrate gave aldehyde 3 presumably via the intermediate 2. Furthermore, ring cleavage at the CO bond of the oxolane moiety in the aldehyde 3 under reductive conditions afforded the eight-membered ring regioselectively.