Skeletal Rearrangements Resulting from Reactions of 1,6:2,3- and 1,6:3,4-Dianhydro-beta-D-hexopyranoses with Diethylaminosulphur Trifluoride
Abstract
A complete series of eight 1,6:2,3- and 1,6:3,4-dianhydro-beta-D-hexopyranoses were subjected to fluorination with DAST. The 1,6:3,4-dianhydropyranoses yielded solely products of skeletal rearrangement resulting from migration of the tetrahydropyran oxygen (educts of D-altro and D-talo configuration) or of the 1,6-anhydro bridge oxygen (D-allo, D-galacto).
The major products yielded by the 1,6:2,3-dianhydropyranoses were compounds arising from nucleophilic substitution, with configuration at C4 either retained (D-talo, D-gulo) or inverted (D-manno), or from C6 migration (D-allo). The minor products in the 1,6:2,3-series resulted from migration of the tetrahydropyran oxygen (D-gulo) or the oxirane oxygen (D-manno), or from nucleophilic substitution with retention of configuration (D-manno).
The structure of most of the rearranged products was verified by X-ray crystallography.