Synthesis of 1,6-anhydro-β- d-talopyranose from derivatives of d-galactose and d-mannose

Abstract

Oxidation of 1,6-anhydro-3,4- O-isopropylidene-β- d-galactopyranose ( 1) with methyl sulfoxide-acetic anhydride or with ruthenium tetraoxide gave the crystalline 2-ketone ( 2) in high yield. Reduction of 2 with lithium aluminum hydride or sodium borohydride gave the d- talo isomer( 3) of 1 stereospecifically. The same reducing agents converted 1,6-anhydro-2,3- O-isopropylidene-β- d- lyxo-hexopyranos-4-ulose ( 4) stereospecifically into 1,6-anhydro-2,3- O-isopropylidene-β- d-talopyranose ( 5). Reduction of 4 with hydrogen over palladium gave a 3:1 mixture of 5 and its d- manno isomer ( 7); and, under these conditions, 2 was converted into a 1:1 mixture of 3 and 1. Mild hydrolysis of 3 or 5 gave 1,6-anhydro-β- d-talopyranose ( 6), the last 1,6-anhydro-β- d-aldohexopyranose to be described; further hydrolysis gave d-talose. N.m.r. spectral data are given for the triacetate ( 8) of 6. The ketones 2 and 4 showed optically active absorption at 330 and 300 nm, respectively, which gave rise in each case to a negative circular dichroism curve, and a Cotton effect of negative sign in the o.r.d. spectrum