Substituent effects on the SmI2/Pd(0)-promoted carbohydrate ring-contraction of 5-alkynylpyranosides

✍ Scribed by José M. Aurrecoechea; Jesús H. Gil; Beatriz López

• Book ID: 104205661
• Publisher: Elsevier Science
• Year: 2003
• Tongue: French
• Weight: 297 KB
• Volume: 59
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(03)01103-7

✦ Synopsis

The effect of substituents on the reactivity and stereoselectivity of the SmI 2 /Pd(0)-promoted ring-contraction of 5-alkynylpyranosides has been examined using substrates substituted only at selected positions. While formation of 2-ethynylcyclopentanols takes place efficiently, an internal alkyne did not afford the expected product. The presence of peripheral alkoxy substituents leads to variable stereoselectivities that depend on the number and orientation of such groups. Thus, an isolated OBn substituent at C(3) (carbohydrate numbering) exerts a significant stereochemical control while additional substitution with the same group at C(4) either enhances or drastically reduces stereoselectivity depending on its orientation (a or b, respectively).