Oxyselenation of Diolefins with Phenyl Selenocyanate and Cooper(II) Chloride. Synthesis of Cyclic Ethers

Article abstract of DOI:10.1021/jo00328a006

A general route for cyclic ethers by oxyselenation of diolefins is described.Reaction of cis,cis-1,5-cyclooctadiene with phenyl selenocyanate in the presence of copper(II) chloride in various alcohols, aqueous tetrahydrofuran, or aqueous acetonitrile produces an isomeric mixture of 2,6-bis(phenylseleno)-9-oxabicyclo<3.3.1>nonane (1a) and 2,5-bis(phenylseleno)-9-oxabicyclo<4.2.1>nonane (1b) in a good to excellent yield.The isomer ratio depends on the solvent utilized, and a suitable choice of solvent results in a selective formation of each isomer.Similar treatment of 5-methoxy- and 5-hydroxycyclooctenes also gives an isomeric mixture of 2-(phenylseleno)-9-oxabicyclo<3.3.1>nonane (4a) and its <4.2.1> isomer (4b). 13C NMR spectral data reveal that all phenylseleno groups are on an endo position of the bicyclic ring system in 1a,b and 4a,b, consistent with the trans stereospecificity of the oxyselenation reaction.The application to other diolefins such as 1,5-hexadiene, diallyl ether, diallyl sulfide, or 4-vinylcyclohexene in aqueous acetonitrile as solvent results in the formation of monocyclic and bicyclic ethers bearing two phenylseleno groups (5-8) in good to excellent yields.The reaction proceeds through alkoxy- or hydroxyselenation of one double bond, followed by a transannular attack of the alkoxyl or hydroxyl group on the episelenonium ion which is formed at the other double bond by the attack of another phenyl selenocyanate.