A mercury-catalyzed transetherification cyclization leading to fused cyclic polyethers

Dihydropyran 6 serves as a key intermediate in a route to fused cyclic poly ethers. The dihydropyran was first converted to 2-hydroxy-1-gamma -methoxya llyltetrahydropyrans 10. Mercury trifluoroacetate-catalyzed transetherifica tion cyclization generated new bicyclic dihydropyrans, 12, ready for additi onal rounds of synthesis. Attempted cyclization under stoichiometric condit ions resulted in isolation of cc-mercurial acetal intermediates, 11, that c ould also be converted to the dihydropyran by treatment with ethyl vinyl et her. (C) 2000 Published by Elsevier Science Ltd.