Regioselectivity of Reductive Cleavage of Methyl 4,6-<i>O</i>-Benzylidene-3-deoxyhexopyranosides Containing Fluorine at the 2- or 3-Position with LiAlH<sub>4</sub>–AlCl<sub>3</sub>
作者:Yoko Mori、Naohiko Morishima
DOI:10.1246/bcsj.66.2061
日期:1993.7
Reductive ring-opening reactions of the 4,6-O-benzylidene derivatives of methyl 3-deoxy-β-d-arabino-, 3-deoxy-α-d-ribo-, and 2-O-benzyl-3-deoxy-α-d-ribo-hexopyranosides with LiAlH4 and AlCl3 in the molar ratio of 4 : 4 gave the 4- and 6-O-benzyl derivatives in a ratio of 7 : 3. The product ratios for the reactions of methyl 4,6-O-benzylidene-2,3-dideoxy-2-fluoro-α-d-arabino- and β-d-ribo-hexopyranosides and methyl 2-O-benzyl-4,6-O-benzylidene-3-deoxy-3-fluoro-α-d-gluco- and β-d-allopyranosides were 3 : 2, 2 : 3, 1 : 1, and 3 : 7, respectively. When the molar ratio of the reagents was 2 : 4, however, the product ratios for the reactions of all the above-mentioned 4,6-O-benzylidene derivatives were approximately equal to 4 : 1. The influence of fluorine at C-2 or C-3, as well as that of the molar ratios of LiAlH4 and AlCl3, on the regioselectivity of the reductive cleavage of 4,6-O-benzylidenehexopyranosides are discussed.
甲基 3-脱氧-β-d-阿拉伯苷、3-脱氧-α-d-核苷和 2-O-苄基-3-脱氧-α-d-核六吡喃糖苷的 4,6-O-亚苄基衍生物与 LiAlH4 和 AlCl3 按 4 : 4 的摩尔比进行还原开环反应,得到 4-和 6-O-苄基衍生物,比例为 7 : 3。甲基 4,6-O-亚苄基-2,3-二脱氧-2-氟-α-d-阿拉伯和 β-d-核吡喃糖苷与甲基 2-O-苄基-4,6-O-亚苄基-3-脱氧-3-氟-α-d-葡糖和 β-d-全吡喃糖苷反应的产物比分别为 3:2、2:3、1:1 和 3:7。然而,当试剂的摩尔比为 2 : 4 时,上述所有 4,6-O-亚苄基衍生物反应的产物比约为 4 : 1。本文讨论了 C-2 或 C-3 上的氟以及 LiAlH4 和 AlCl3 的摩尔比对 4,6-O-亚苄基吡喃己糖苷还原裂解反应的区域选择性的影响。