7.
The merits of an indirect protecting method for hydroxyl groups using allyl groups via allyloxycarbonyl groups in the synthesis of antennary β-d-mannopyranosyl disaccharides from β-d-galactopyranosyl disaccharides were studied. Regioselective allyloxycarbonylation and conversion reactions involving simultaneous double S
N2 nucleophilic substitution at C-2′ and C-4′ of benzyl
O-[β-d-galactopyranosyl]-(1-4)-3,6-di-
O-benzyl-2-deoxy-2-
N-phthalimido-β-d-glucopyranoside were examined for comparison with the direct allylation method. The required β-d-mannopyranosyl disaccharide having proper protecting groups was obtained using this indirect method in 52% yield. In contrast, the reported direct allylation method using methyl
O-(β-d-galactopyranosyl) disaccharide gave the corresponding β-d-mannopyranosyl disaccharide in only 7.5% yield.
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