Revisit of the phenol O-glycosylation with glycosyl imidates, BF3·OEt2 is a better catalyst than TMSOTf
作者:Yali Li、Huaping Mo、Gaoyan Lian、Biao Yu
DOI:10.1016/j.carres.2012.09.025
日期:2012.12
With BF(3)·OEt(2) as the catalyst, the glycosylation of phenols with glycosyl trichloroacetimidates (or N-phenyl trifluoroacetimidates) bearing 2-O-participating groups leads to the desired 1,2-trans-O-glycosides in generally excellent yields without formation of the 1,2-cis-anomers. However, with TMSOTf as the catalyst, the outcomes of the corresponding phenol O-glycosylation are highly dependent
以BF(3)·OEt(2)为催化剂,苯酚与带有2-O-参与基团的糖基三氯乙酰基亚氨酸盐(或N-苯基三氟乙酰基亚氨酸盐)的糖基化反应通常会产生所需的1,2-反式-O-糖苷极佳的收率,而不会形成1,2-顺式端基异构体。然而,以TMSOTf为催化剂,相应的酚O-糖基化的结果高度依赖于酚的亲核性。苯酚的亲核性越少,生成的1,2-顺式-O-糖苷含量越高,副产物就越多。在所有这些酚O-糖基化反应中,发现1,2-原酸酯是低温(<-70°C)的主要产物,在较高温度下转化为最终产物。BF(3)·OEt(2)是促进1转化的有效催化剂 将2-原酸酯转化为相应的1,2-反式-O-糖苷。然而,在TMSOTf存在下,1,2-原酸酯可被转化为三氟甲磺酸二恶唑鎓和三氟甲磺酸糖基酯,这些中间体可能与糖基氧碳鎓相关物种处于平衡状态,最终形成α/β-O-的最终混合物。苷和副产物。