Redox glycosidation: the use of Nozaki-Takai methylenylation in a highly stereoselective synthesis of sucrose.
Sequential reaction of 2,3,4,6-tetra-O-benzyl-D-glucopyranose (7) with butyllithium and 2-[2,3,5-tri-O-benzyl-4-O-(tert-butyldiphenylsilyl)-D- arabinonoyl]thio-3-nitropyridine (6) at -78 degrees gave 2,3,4,6-tetra-O-benzyl-alpha-D-glucopyranosyl 2,3,5-tri-O-benzyl-4-O-(tert-butyldiphenylsilyl)-D-arabinonate+ ++ (8; 71%, alpha:beta greater than 50:1). Ester carbonyl methylenylation, desilylation, and iodoetherification in the presence of silica gave 3,4,6-tri-O-benzyl-1-deoxy-1-iodo-(2,3,4,6-tetra-O-benzyl-alpha-D- glucopyranosyl)-beta-D-fructofuranoside (15; 44%, alpha:beta greater than 50:1). This neopentylic iodide 15 was converted into sucrose (1;80%) by free-radical substitution using TEMPO (24) followed by sodium-ammonia reduction, acetylation, and Zemplén methanolysis.
Barrett
A G
AG
Department of Chemistry, Colorado State University, Fort Collins 80523.
Melcher
L M
LM
Bezuidenhoudt
B C
BC
D006027:Glycosides / Q000737:chemistry*; D008745:Methylation; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D013395:Sucrose / Q000138:chemical synthesis*
D006027:Glycosides; D013395:Sucrose