Fluorocarbohydrates. Part XVII. Formation of 2,5-anhydro-1-deoxy-1,1-difluoro-D-mannitol by fluorination of acetylated glucals

Abstract

3,4,6-Tri-O-acetyl-D-glucal undergoes ring-contraction in a reaction with lead tetra-acetate in anhydrous hydrogen fluoride giving, after deacetylation and chromatographic purification, a non-crystalline product, 2,5-anhydro-1-deoxy-1,1-difluoro-D-mannitol. This product consumed 0·9 mol of sodium metaperiodate, and could be converted into a trimethyl ether and into a crystalline tri-O-toluene-p-sulphonate. Oxidation of the difluoroanhydromannitol with hot chromic acid yielded difluoroacetic acid. Ethyl 4,6-di-O-acetyl-2,3-didehydro-2,3-dideoxy-α-D-erythro-hexoside (a derivative of ψ-glucal) was fluorinated as above giving the same difluoroanhydro-mannitol. The manno-configuration was established by periodate oxidation, and borohydride reduction to an optically active triol (characterised as the crystalline tri-O-p-nitrobenzoate).