Absence of Stereodirecting Participation by 2-<i>O</i>-Alkoxycarbonylmethyl Ethers in 4,6-<i>O</i>-Benzylidene-Directed Mannosylation
作者:Peng Wen、David Crich
DOI:10.1021/acs.joc.5b02203
日期:2015.12.18
β-selectivities and absence of cyclic products observed with the 2-O-(methoxycarbonylmethyl) ether exclude the effective participation of esters through six-membered cyclic intermediates in this series. The results are discussed in terms of the conformation of cyclic dioxenium ions (E,E-, E,Z-, or Z,Z-) and in the context of “neighboring group” participation by nonvicinal esters in glycosylation. Methods
描述了一系列带有2- O-(2-氧代烷基)醚的甘露聚糖基供体的制备及其在糖基化反应中的用途。用简单的2- O-苯甲酰基醚和2- O-(叔丁氧基羰基甲基)醚形成环状产物建立了参与这种系统的立体电子可行性。用双三氟甲基苯甲醚观察到的高β-选择性表明,可以通过引入吸电子取代基来抑制参与。用2- O观察到高的β选择性和不存在环状产物-(甲氧羰基甲基)醚排除了酯通过该系列六元环状中间体的有效参与。将根据环状二恶烯离子(E,E-,E,Z-或Z,Z-)的构象,以及非邻位酯参与糖基化的“相邻基团”来讨论结果。描述了用于2- O-苯甲酰基和2- O-(甲氧基羰基甲基)醚的脱保护的方法。