REACTIONS OF PHENYL CHLOROSULFATE AT OH-2 AND OH-3 OF ALDOHEXOPYRANOSE DERIVATIVES. COMPETING SUBSTITUTION AND DISPLACEMENT REACTIONS

Article abstract of DOI:10.1016/0008-6215(89)84145-X

Reactions of phenyl chlorosulfate-sodium hydride with methyl 4,6-O-benzylidenealdohexopyranosides are characterized by a variety of nucleophilic substitution and displacement processes involving OH-2 and -3 of the glycosides.Depending on such factors as the relative rates of substitution of these two hydroxyl groups and their configurations, as well as temperature and stoichiometry, the products may be mono- or di-phenylsulfates (or both), 2,3-cyclic sulfates, or 2,3-oxiranes.For example, in the reaction of methyl 4,6-O-benzylidene-α-D-glucopyranoside with two equivalents of phenyl chlorosulfate at +25^deg, the products were the 2,3-disulfate (10percent), 2,3-cyclic sulfate (77percent), and 2,3-allo epoxide (4percent), whereas, at -25^deg, by far the major product was the 2-phenylsulfate (79percent).Intramolecular displacement was so readily facilitated in the reaction of methyl 4,6-O-benzylidene-α-D-altropyranoside that the only products obtained were the 2,3-anhydro-manno- (major) and -allo-pyranosides.Conformations of the 2,3-cyclic sulfates are considered on the basis of their n.m.r. characteristics.