Samarium Diiodide Promoted C-Glycosylation: An Application to the Stereospecific Synthesis of α-1,2-C-Mannobioside and Its Derivatives

✍ Scribed by Olivier Jarreton; Troels Skrydstrup; Juan-Félix Espinosa; Jesús Jiménez-Barbero; Jean-Marie Beau

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 223 KB
• Volume: 5
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/(sici)1521-3765(19990201)5:2<430::aid-chem430>3.0.co;2-d

✦ Synopsis

The synthesis of the C-glycoside analogue of the disaccharide Man-(a1 32)Man has been achieved in a highly stereoselective and efficient manner employing an approach which closely parallels O-glycoside synthesis. The key step included the samarium diiodide reduction of mannosyl pyridylsulfone 18 in the presence of the C2-formyl branched mannoside derivative 17 a to furnish the C-disaccharide derivative 19 a in high yield. An intramolecular formyl group transfer reaction by means of 5-exo radical cyclization and concomitant fragmentation yielded aldehyde 17 a stereospecifically. We also present a potentially viable alternative for the deoxygenation of sterically encumbered secondary alcohols. Attempts to extend this procedure to the synthesis of the C-trisaccharide of Man(a1 32)Man(a1 32)Man were frustrated by the inability of the disaccharide, pyridylsulfone derivative 43, to undergo coupling with carbonyl substrates upon treatment with SmI 2 , possibly owing to the sterically bulky C2 substituent.