Step-wise oxidation of the two double bonds in 1-alkoxycarbonyl-3-cyano-1, 4- or -1, 6-dihydropyridine (6 or 5) was found to be possible and 5-methoxycarbonyl-5-deoxy-dl-xylopiperidinose tetraacetate (18a) was synthesized via 5, 12, 13, and 17 from nicotinonitrile.
