Iodine-catalyzed synthesis of five-membered cyclic ethers from 1,3-diols under solvent-free conditions.

Intramolecular etherification of 1,3-diols was investigated using iodine as a catalyst under solvent-free conditions. The reaction proceeded to completion in a heterogeneous system. Five-membered cyclic ethers were obtained by intramolecular cyclization of 1,3-diols with dehydration. A propella ether (11-oxatricyclo[4.4.3.0(1,6)]tridecane) was conveniently synthesized from a 1,3-diol (6-(2-hydroxyethyl)spiro[4.5]decan-6-ol) in 86% yield with carbon skeleton rearrangement under the following conditions: a temperature of 60 degrees C, a molar ratio of 1,3-diol:iodine = 1:0.2, and a time period of 3 h. Bicyclic ethers were also obtained from the corresponding 1,3-diols, but spiro ethers were obtained in lower yield. Terpenic cyclic ethers were efficiently synthesized from the corresponding 1,3-diols, derived from (+)-camphor and (-)-fenchone. In the case of etherification with a mechanism of carbon skeleton rearrangement, the yield of the solvent-free reaction was as high as that of the corresponding reaction in solution. Etherification reactions with carbon skeleton rearrangement proceeded more smoothly than those with hydride shift.