Unsaturated carbohydrates. Part IV. Allylic rearrangement reactions of 3,4,6-tri-O-acetyl-D-galactal

Abstract

Reaction of tri-O-acetyl-D-galactal with alcohols and phenols is shown to give glycoside derivatives containing a 2,3-double bond. In boiling acetic acid the glycal acetate undergoes competing addition and rearrangement reactions, and ultimately gives a diene which is assigned a pyranoid structure; crystalline 1,3,4,6-tetra-O-acetyl-2-deoxy-α-D-lyxo-hexose, 3,4,6-tri-O-acetyl-D-gulal, and 1,4,6-tri-O-acetyl-2,3-didehydro-2,3-dideoxy-α-D-threo-hexose have been isolated. The same products can be obtained by heating the saturated acetate in acetic acid. In the presence of added methanesulphonic acid, only minor amounts of unsaturated compounds are formed from the glycal ester.

The product of alkaline degradation of 2-deoxy-D-lyxo-hexose has been studied briefly.