Two new carbaaldohexofuranoses, carba--D-glucofuranose and carba--L-mannofuranose have been prepared using 5,6-O-isopropylidene-D-glycero-L-galacto-heptono-1,4-lactone (6) as the starting material. The key step was a highly stereoselective intramolecular 5-exo-trig radical cyclisation of C-2-substituted 2,3-unsaturated 7-bromo-7-deoxy-heptono-1,4-lactones promoted by tributyltin hydride. Assignment of the configuration of the unsaturated lactones was based upon NMR data of related compounds. The starting material, compound 6, was obtained by chain elongation of D-gulose, and a facile method for separation of the epimers from the chain elongation has been developed, thus 5,6-O-isopropylidene-D-glycero-L-galacto-heptono-1,4-lactone (6) and D-glycero-L-talo-heptono-1,4-lactone (5) were isolated in ca. 30% and 10% yield, respectively.
|Publication status||Published - 1999|