Glycosylidene Carbenes. Part 7. Neighbouring-group participation by the 2-benzyloxy group in the glycosidation of strongly acidic hydroxy compounds
✍ Scribed by Yoshikazu Takahashi; Andrea Vasella
- Book ID
- 102860364
- Publisher
- John Wiley and Sons
- Year
- 1992
- Tongue
- German
- Weight
- 565 KB
- Volume
- 75
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
Abstract
To demonstrate the neighbouring‐group participation of the 2‐benzyloxy group in the glycosidation of phenols and of strongly acidic alcohols by the diazirine 1, we examined the glycosidation of 4‐nitrophenol, 4‐methoxyphenol, (CF~3~)~2~CHOH, MeOH, and i‐PrOH by the diazirine 11, derived from the 2‐deoxypyranose 6. Oxidation of the oximes 7 yielded (E)‐ and (Z)‐8. In solution, (E)‐8 isomerised to (Z)‐8. Similarly, the (E)‐configurated mesylate 9, prepared from 8, underwent acid‐catalysed isomerisation to (Z)‐9. Treatment of (Z)‐9 with NH~3~, followed by oxidation of the resulting diaziridine 10 with I~2~, yielded the desired diazirine 11. Glycosidation by 11 of the above mentioned hydroxy compounds yielded the glycosides 12–21. In agreement with the postulated neighbouring‐group participation, these glycosidation proceeded without, or with a very low diastereoselectivity, favouring the axial anomers.