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Hydroformylation of 5,6-anhydro-1,2- O -isopropylidene-α- D -glucofuranose ( 1 ) with carbon monoxide and hydrogen in the presence of dicobalt octacarbonyl for 1.5 h at 105° gave 6-deoxy-1,2- O -isopropylidene-α- D -gluco-heptodialdo-1,4-furanose- 7,3-pyranose ( 5 ) and 6-deoxy-1,2- O -isopropylidene-α- D - xylo -hexofuranos-5-ulose ( 3 ) in 78 and 7% yields, respectively. The dialdose 5 was acetylated to afford the diacetate 6 , which was fused with 5,6-dimethylbenzimidazole in the presence of monochloroacetic acid to afford an anomeric mixture of nucleosides 7a and 7b .