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 > 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 > 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 Zemplen methanolysis.