On the Role of Neighboring Group Participation and Ortho Esters in β-Xylosylation: <sup>13</sup>C NMR Observation of a Bridging 2-Phenyl-1,3-dioxalenium Ion
作者:David Crich、Zongmin Dai、Stéphane Gastaldi
DOI:10.1021/jo990424f
日期:1999.7.1
The role of ortho esters in the formation of 2,3,4-tri-O-benzoyl-β-xylopyranosides from various donor/promoter pairs has been investigated. It is concluded that for the activation of sulfoxides with Tf2O, thioglycosides with PhSOTf, and bromides with AgOTf the anomeric configuration of the donor is of no consequence on the outcome of the reaction. In all methods studied, the presence or absence of
已经研究了原酸酯在从各种供体/启动子对形成 2,3,4-三-O-苯甲酰基-β-吡喃木糖苷中的作用。结论是,对于用 Tf2O 活化亚砜,用 PhSOTf 活化硫糖苷,用 AgOTf 活化溴化物,供体的异头构型对反应结果没有影响。在所有研究的方法中,非亲核受阻碱的存在与否至关重要,原酸酯只有在其存在时才能辨别。S-Phenyl 2,3,4-tri-O-benzoyl-1-deoxy-1-thia-β-d-xylopyranoside 合成在三个羰基碳的每一个上都富含 13C。在 CD2Cl2 中,在 -78 °C 下,无论是否有碱许可,用 PhSOTf 激活这种硫糖苷,这是第一次,通过 13C NMR 光谱观察桥接二氧戊环离子作为相邻基团定向糖基化中的中间体。在碱存在的情况下猝灭该阳离子产生原酸酯,而在没有碱的情况下,糖苷是唯一检测到的产物。