A Synthetic Study on Trans-2,5-Disubstituted Tetrahydrofurans via Phenylselenoetheriflcation

A Synthetic Study on Trans-2,5-Disubstituted Tetrahydrofurans via Phenylselenoetheriflcation

2,5-Disubstituted tetrahydrofurans 11-13 were prepared by phenylselenoetherification of 1-alkyl-4-phenyl-(3E)-butenols 8-10 under kinetic conditions. Their stereochemical outcome and reactivity were controlled by solvent, reaction temperature and the alkyl substituent. While the cyclization was stereorandom in dichloromethane, its stereoinduction was moderate to good in propionitrile and good to excellent in diethyl ether. The reaction went to completion in dichloromethane and propionitrile, but it did not in diethyl ether. The results can be rationalized by the degree of reversibility in the formation of episelenonium cation and 1,3-diaxial interactions in the transition state of the formation of tetrahydrofuranonium cation.