PREPARATION OF 4,6-CYCLO-4,6-DIDEOXY-HEXOPYRANOSES BY PALLADIUM-MEDIATED INTRAMOLECULAR CYCLODEHALOGENATION

4,6-Cyclo-4,6-dideoxy-hexopyranoses were obtained by palladium-mediate d intramolecular cyclodehalogenation. Thus, methyl yl-4,6-dideoXY-4,6- diiodo-beta-D-galactopyranoside (3) afforded methyl tyl-4,6-cyclo-4,6- dideoxy-beta-D-galactopyranoside (5) in 56% yield upon treatment with hydrogen in the presence of palladium-on-charcoal and diethylamine. Th e structure of 5 was proven by MS, NMR including NOE measurements, and by independent conversion of 4 to 5 by zinc-mediated Wurtz synthesis. Similarly, methyl yl-4,6-cyclo-4,6-dideoxy-alpha-D-galactopyranoside (6) and 4,6-cyclo-4,6-dideoxy-alpha-D-galactopyranosyl)-(l --> 4)-1,2, 3,6-tetra-0-acetyl-beta-D-glucopyranose (17) were obtained along with the respective 4,6-dideoxy analogues. Also methyl etyl-4,6-dideoxy-4,6 -diiodo-beta-D-glucopyranoside (19) gave galacto-configured 5 stereose lectively.