present the novel synthesis of two sugar units that are central intermediates for the formation of members of the bicyclo-DNA and -RNA family. The synthesis starts from commercially available 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose. The key step involves the elaboration of a carbocyclic ring in a furanoside by rhodium(I)-catalyzed hydroacylation. Via this pathway, one of the sugar units is available