A mercury-catalyzed transetherification cyclization leading to fused cyclic polyethers

Dihydropyran 6 serves as a key intermediate in a route to fused cyclic polyethers. The dihydropyran was first converted to 2-hydroxy-1-γ-methoxyallyltetrahydropyrans, 10. Mercury trifluoroacetate-catalyzed transetherification cyclization generated new bicyclic dihydropyrans, 12, ready for additional rounds of synthesis. Attempted cyclization under stoichiometric conditions resulted in isolation of α-mercurial acetal intermediates, 11, that could also be converted to the dihydropyran by treatment with ethyl vinyl ether.