Thermal and Photochemical Epimerization/Equilibration of Carbohydrate Cobaloximes
作者:Gui-Xue Yu、David R. Tyler、Bruce P. Branchaud
DOI:10.1021/jo005595v
日期:2001.8.1
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-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.