Preparation of some fully chloroacetylated glycopyranosyl bromides: Useful intermediates for the synthesis of base- and hydrogenolysis-sensitive glycosides
✍ Scribed by Ziegler, Thomas
- Book ID
- 102901346
- Publisher
- John Wiley and Sons
- Year
- 1990
- Tongue
- English
- Weight
- 804 KB
- Volume
- 1990
- Category
- Article
- ISSN
- 0947-3440
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✦ Synopsis
Abstract
Chloroacetylation of alkyl glycopyranosides of β‐D‐galactose, β‐D‐glucose and α‐D‐mannose as well as of free D‐glucose, D‐galactose, D‐mannose and D‐xylose, using chloroacetic anhydride as acylating reagent, gave the corresponding fully chloroacetylated pyranose derivatives in excellent yields. From D‐glucose, 1,2,3,6‐tetra‐O‐chloroacetyl‐α‐D‐glucopyranose (9) was also obtained. Subsequent treatment of the fully chloroacetylated α‐D‐glycopyranoses 3, 8, 13 and 15 of galactose, glucose, mannose, and xylose, respectively, with HBr resulted in 2,3,4,6‐tetra‐O‐chloroacetyl‐α‐D‐galactopyranosyl bromide (4, 98%), ‐glucopyranosyl bromide (10, 92%), ‐mannopyranosyl bromide (14, 72%) and 2,3,4‐tri‐O‐chloroacetyl‐α‐D‐xylopyranosyl bromide (16, 68%). 10 reacted with D‐pantholactone (17) and silver trifluoromethanesulfonate under acidic conditions to give the corresponding α‐linked (18, 45%) and β‐linked (20, 38%) glucopyranosides. Under basic conditions the corresponding ortho ester product 21 was formed (92%) which upon treatment with BF~3~ gave the glucosides 18 and 20. Silver silicate as the catalyst gave only traces of 18. Thus, 20 was isolated in 80% yield. Reaction of 10 with silver crotonate and silver laurate gave 1‐O‐crotonoyl‐ (22) and 1‐O‐lauroyl‐2,3,4,6‐tetra‐O‐chloroacetyl‐β‐D‐glucopyranose (24), respectively. 18 and 22 were dechloroacetylated with thiourea, affording the corresponding deblocked glucose derivatives 19 and 23, respectively.