Synthesis of kojitriose using silicon-tethered glycosidation

Reaction of 3,4,6-tri-O-acetyl-beta-D-glucopyranosyl chloride (1) with potassium phenylselenate gave phenyl 3,4,6-tri-O-acetyl-1-seleno-alpha, beta-D-glucopyranoside (2) in 59% yield. Silylation of benzyl 3,4,6-tri-O-benzyl-beta-D-glucopyranoside (4) with ethyl 3,4,6-tri-O-benzyl-2-O-chlorodimethylsilyl-1-thio-beta -D-glucopyranoside gave benzyl 2-O-(3,4, 6-tri-O-benzyl-1-S-ethyl-1-thio-beta-D-glucopyranos-2-O-yldimet hylsilyl)-3,4,6,-tri-O-benzyl-beta-D-glucopyranoside (5) in 35% yield. Reaction of 5 with N-iodosuccinimide in nitromethane gave benzyl 2-O-(3,4, 6-tri-O-benzyl-alpha-D-glucopyranosyl)-3,4, 6-tri-O-benzyl-beta-D-glucopyranoside (6) in 45% yield. Chlorodimethylsilylation of phenyl 3,4, 6-tri-O-acetyl-1-seleno-alpha-D-glucopyranoside (2 alpha) and reaction with 6 gave benzyl 2-O-[2-O-(3,4,6 -tri-O-acetyl-1-Se-phenyl-1-seleno-alpha-D-glucopyranos-2-O-yld imethylsilyl) -3,4,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3,4,6-tri-O-benzyl-beta-D- glucopyranoside (7) in 82% yield. Intramolecular glycosidation of 7 using N-iodosuccinimide in nitromethane gave benzyl 2-O-[2-O-(3,4,6-tri-O-acetyl-alpha-D-glucopyranosyl)-3, 4,6-tri-O-benzyl-alpha-D-glucopyranosyl]-3, 4,6-tri-O-benzyl-beta-D-glucopyranoside (8) in 45% yield. Deprotection of 8 gave kojitriose (9) in quantitative yield. Chlorodimethylsilylation of 1,3,4,6-tetra-O-benzyl-alpha, beta-D-fructofuranose (10) with dimethyldichlorosilane and pyridine followed by reaction with ethyl 3,4, 6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (3) gave ethyl 2-O-(1,3,4,6-tetra-O-benzyl-alpha, beta-D-fructofuranosyloxydimethylsilyl)-3,4, 6-tri-O-benzyl-1-thio-beta-D-glucopyranoside (11) in 85% yield. Chlorodimethylsilylation of 1,3,4, 6-tetra-O-benzoyl-alpha-D-fructofuranose (12) with dimethyldicholorosilane and triethylamine followed by reaction with phenyl 3,4, 6-tri-O-acetyl-1-thio-alpha-D-glucopyranoside (13) gave phenyl 2-O-(1,3,4, 6-tetra-O-benzoyl-alpha-D-fructofuranosyloxydimethylsilyl)-3, 4,6-tri-O-acetyl-1-thio-alpha-D-glucopyranoside (14) in 62% yield. Both 11 and 14 failed to undergo intramolecular glycosidation.