Stereoselective synthesis of substituted tetrahydropyran rings via 6-exo and 6-endo selenoetherification

Eight unsaturated alcohols were cyclized by selenoetherification in 6-exo or 6-endo manner to give substituted tetrahydropyran rings. Yields, regio- and stereoselectivities were discussed in terms of steric and electronic effects such as Se-O interaction. For the first time examples of the use of silica gel in selenoetherification and the effect of the X^- counter ion of PhSe⁺ on the reaction course are discussed. These effects are related to the occurrence of Se-O interaction.