Thermal and photochemical epimerization/equilibration of carbohydrate cobaloximes.
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-pyridyldimethylglyoximatocobalt-1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose 4 for the 4:5 epimer pair, exo-3-deoxy-3-pyridyldimethylglyoximatocobalt-5-O-carboxymethyl-1,2-O-isopropylidene-alpha-D-xylofuranose 9 for the 9:10 epimer pair, and equatorial 1-deoxy-1-pyridyldimethylglyoximatocobalt-2,3,4,6-tetra-O-benzyl-beta-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)(2)Co(*) radicals with alkyl R(*) free radicals, with the preferred kinetic path leading to the more stable product.
Yu
G X
GX
Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253, USA.
Tyler
D R
DR
Branchaud
B P
BP
D003038:Cobamides / Q000138:chemical synthesis / Q000737:chemistry*; D006358:Hot Temperature; D007536:Isomerism; D007700:Kinetics; D010091:Oximes / Q000138:chemical synthesis / Q000737:chemistry*; D010777:Photochemistry; D013816:Thermodynamics
D003038:Cobamides; D010091:Oximes