Stereoselective Synthesis of the alpha-Allyl C-Glycoside of 3-Deoxy-D-manno-2-octulosonic Acid (KDO) by Use of Radical Chemistry.

Methyl 2-C-allyl-2,6-anhydro-3-deoxy-4,5:7,8-di-O-isopropylidene-D-glycero- D-talo-octonate (9a), the protected alpha-allyl C-glycoside of 3-deoxy-D-manno-2-octulosonic acid (KDO), has been synthesized using a photochemically initiated radical reaction. A phenyl thioglycoside (8) was used as the substrate and allyltributyltin as the acceptor. The stereoselectivity of the reaction was 90:10 in favour of the talo-isomer (alpha-).