Stereoselective synthesis of cis- and trans-2,5-disubstituted tetrahydrofurans

A general route to either cis- or trans-2, 5-disubstituted tetrahydrofurans was described by using the nucleophilic addition of organolithium derivatives to tricyclic lactones, followed by a highly stereocontrolled acid-assisted reduction with sodium cyanoborohydride of the hemiketals formed. The stereoselectivity observed can be rationalized by the preferential approach of the hydride on the less hindered face of an oxonium ion intermediate. The cis- or trans-2, 5-disubstituted tetrahydrofurans were provided by the hot decomposition and then hydrogenation of tricycle compounds produced.