Add time:09/10/2019         Source:sciencedirect.com

The title compounds 5-O-acetyl-1,2-anhydro-3-O-benzyl-α-d-ribofuranose and 5-O-acetyl-1,2-anhydro-3-O-benzyl-β-d-lyxofuranose, and 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-α-d-glucopyranose and 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-β-d-talopyranose, and 5-O-acetyl-1,2-anhydro-3,6-di-O-benzyl-β-d-mannofuranose and 1,2-anhydro-5,6-di-O-benzoyl-3-O-benzyl-β-d-mannofuranose have each been synthesized from the corresponding 2-O-tosylate and 1-free hydroxyl intermediates by base-initiated intramolecular SN2 ring closure in almost quantitative yields. Acetyl and benzoyl groups were not affected in the ring closure reactions. Condensation of 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-α-d-glucopyranose and 5-O-acetyl-1,2-anhydro-3,6-di-O-benzyl-β-d-mannofuranose with 1,2:3,4-di-O-isopropylidene-α-d-galactopyranose in the presence of ZnCl2 as the catalyst afforded the 1,2-trans-linked 6-O-acetyl-3,4-di-O-benzyl-β-d-glucopyranosyl-(1→6)-1,2:3,4-di-O-isopropylidene-α-d-galactopyranose and 5-O-acetyl-3,6-di-O-benzyl-α-d-mannofuranosyl-(1→6)-1,2:3,4-di-O-isopropylidene-α-d-galactopyranose as the sole products in satisfactory yields, while condensation of 5-O-acetyl-1,2-anhydro-3-O-benzyl-β-d-lyxofuranose with 3-O-benzyl-1,2-O-isopropylidene-α-d-xylofuranose yielded the 1,2-trans-linked 5-O-acetyl-3-O-benzyl-α-d-lyxofuranosyl-(1→5)-3-O-benzyl-1,2-O-isopropylidene-α-d-xylofuranose as the sole product in a good yield. The 6-O-acetyl group in the glycosyl donor, 6-O-acetyl-1,2-anhydro-3,4-di-O-benzyl-α-d-glucopyranose, did not influence the stereoselectivity of the ring-opening–coupling reaction.

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