摘要 : The reaction of 2,3,4-tri-O-benzyl-#alpha#-L-rhamnopyranosyl fluoride (6-deoxy-2,3,4-tri-O-benzyl-#alpha#-L-mannopyranosyl fluoride) with 2,4-dibenzylphloroacetophenone,in the presence of boron trifluoride·diethyl etherate,afforde... 展开 The reaction of 2,3,4-tri-O-benzyl-#alpha#-L-rhamnopyranosyl fluoride (6-deoxy-2,3,4-tri-O-benzyl-#alpha#-L-mannopyranosyl fluoride) with 2,4-dibenzylphloroacetophenone,in the presence of boron trifluoride·diethyl etherate,afforded both the 3-C-#alpha#-L- and the 3-C-#beta#-L-rhamnopyranosylphloroacetophenone derivatives.The 3-C-#alpha#-L-rhamnoside was produced as a major product,while the 3-C-#beta#-L-rhamnoside was produced as a minor product via anomerization of the 3-C-#alpha#-L-rhamnoside.Alternatively,the reaction of 2,3,4,6-tetra-O-benzyl-#alpha#-D-mannopyranosyl fluoride with 2,4-dibenzylphloroacetophenone afforded both the 3-C -#alpha#-D- and the 3-C-#beta#-D-mannnopyranosylphloroacetophenone derivatives under identical conditions.The 3-C-#beta#-D-mannoside was produced as a major product via anomerization of the 3-C-#alpha#-D-mannoside during the reaction.These differences in composition result apparently from the magnitude of the 1,3-diaxial interactions between the C-3 and C-5 positions in these sugar moieties. 收起