New accesses to l-iduronyl synthons

(PhS)3CLi adds with a total l-ido selectivity onto 3-O-benzyl-1,2-O-isopropylidene-α-d-xylo-dialdose 2, opening the way to the most efficient preparation of 1,2,4-tri-O-acetyl-3-O-benzyl-l-iduronyl synthon 8. Alternatively, in view of combinatorial syntheses, aldehyde 2 allows a good access to vinylic l-ido and d-gluco synthons which may be converted into uronic acid by a sequence involving a new aldehyde oxidation by m-CPBA in aqueous solution.