THE MECHANISMS OF THE HALOGENATIONS AND HALOGENOMETHOXYLATIONS OF D-GLUCAL TRIACETATE, D-GALACTAL TRIACETATE, AND 3,4-DIHYDROPYRAN

The stereochemical routes of the reactions showed trends, when the halogen, the olefin, and the solvent were changed, which can be accounted for on the basis of (a) the relative stabilities of the halonium and oxocarbonium ions formed as intermediates, (b) the effect of ring conformation on the ease of formation of oxocarbonium ions involving the ring-oxygen of the pyranose ring, (c) the role of the anomeric effect in determining the stability of the transition state, and (d) the influence on the route of reaction of whether or not the intermediate cations are solvated by a nucleophile as they are formed. Proton magnetic resonance spectroscopy was extensively used to determine the compositions of products and the configurations and conformations of the compounds obtained.