Redox glycosidation: the use of Nozaki-Takai methylenylation in a highly stereoselective synthesis of sucrose

Abstract

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° gave 2,3,4,6-tetra-O-benzyl-α-d-glucopyranosyl 2,3,5-tri-O-benzyl-4-O-(tert-butyldiphenylsilyl)-d-arabinonate (8; 71%, α:β > 50:1). Ester carbonyl methylenylation, desilylation, and iodoetherification in the presence of silica gave 3,4,6-tri-O-benzyl-1-deoxy-1-iodo-(2,3,6-tetra-O-benzyl-α-d-glucopyranosyl)-β-d-fructofuranoside (15; 44%, α:β > 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. © 1992.