Synthesis, conformation, and glycosidic coupling reactions of highly active substituted 2,7-dioxabicyclo[4.1.0]heptanes: 1,2-anhydro-3,4-di-O-benzyl-α-d-xylopyranose

✍ Scribed by Guangbin Yang; Fanzuo Kong; Robert R. Fraser

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 734 KB
• Volume: 258
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(94)84074-1

✦ Synopsis

The title 1,Zanhydro sugar (8) was synthesized from D-xylose. The key intermediate for the synthesis was 2-0-acetyl-3,4-di-0-benzyl-@-o-xylopyranosyl fluoride, which was transformed into crystalline 8 by ring closure with potassium tert-butoxide. Comparison of the observed vicinal coupling constants for 8 with the results obtained from calculations by molecular mechanics suggested that the conformation of the pyranose ring is close to a 4Hg half chair. The anhydro sugar was highly reactive, its condensation with 1,2 : 3,4-di-o-isopropylidene-cu-D-galactopyranose proceeding in reasonable yield without any Lewis acid catalyst, and quantitatively in the presence of molecular sieves to give the P-linked disaccharide as the major product. The stereochemical outcome of the condensation was little affected by changes in' solvent or reaction temperature.

The presence of some Lewis acid catalysts caused a decrement in the p : LY ratio, while predominantly a-linked disaccharide was obtained when trityl perchlorate was the catalyst.