Epimeric carbohydrate alkyl cobaloximes 4:5, 9:10, and 12:13 can be equilibrated thermally or photochemically. In each case, one isomer is strongly favored: exo-3-deoxy-3-pyridyldimethylgly-oximatocobalt-1, 2:5,6-di-O-isopropylidene-α-D-glucofuranose 4 for the 4:5 epimer pair, exo-3-deoxy-3-pyridyldimethylglyoximatocobalt-5-O-carboxymethyl-1, 2-O-isopropylidene-α-D-xylofuranose 9 for the 9:10 epimer pair, and equatorial 1-deoxy-1-pyridyldimethylglyoximatocobalt-2,3,4, 6-tetra-O-benzyl-β-D-glucopyranose 12 for the 12:13 epimer pair. These data indicate that there is a strong facial preference for the coupling of py(dmgH)2Co· radicals with alkyl R· free radicals, with the preferred kinetic path leading to the more stable product.
ASJC Scopus subject areas
- Organic Chemistry