Absence of Stereodirecting Participation by 2-O-Alkoxycarbonylmethyl Ethers in 4,6-O-Benzylidene-Directed Mannosylation.
Absence of Stereodirecting Participation by 2-O-Alkoxycarbonylmethyl Ethers in 4,6-O-Benzylidene-Directed Mannosylation.
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4,6-O-亚苄基定向甘露糖基化中 2-O-烷氧基羰基甲基醚不存在立体定向参与。
DOI：
10.1021/acs.joc.5b02203
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Crich,David
中科院分区：
文献类型：
--
作者：
Wen,Peng;Crich,David
本文报道了一系列带有2-O-（2-氧代烷基）醚的吡喃甘露糖供体的制备及其在糖基化反应中的应用。与简单的2-O-苯甲酰甲基醚和与2-O-（叔丁氧基羰基甲基）醚的环状产物的形成确立了参与此类系统的立体电子可行性。用双-三氟甲基苯甲酰甲基醚观察到的高β-选择性表明，通过引入吸电子取代基可以抑制参与。用2-O-（甲氧羰基甲基）醚观察到的高β-选择性和不存在环状产物排除了酯通过六元环状中间体在该系列中的有效参与。结果进行了讨论，在环dioxenium离子（E，E-，E，Z-，orZ，Z-）的构象和在上下文中的“邻基”参与的nonvicinal酯在糖基化。描述了2-O-苯甲酰甲基和2-O-（甲氧羰基甲基）醚的脱保护方法。
The preparation of a series of mannopyranosyl donors carrying 2-O-(2-oxoalkyl) ethers and their use in glycosylation reactions are described. The formation of cyclic products with the simple 2-O-phenacyl ether and with the 2-O-(t-butoxycarbonylmethyl) ether establishes the stereoelectronic feasibility of participation in such systems. The high β-selectivities observed with the bis-trifluoromethyl phenacyl ether indicate that participation can be suppressed through the introduction of electron-withdrawing substituents. The high 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-, orZ,Z-) and in the context of “neighboring group” participation by nonvicinal esters in glycosylation. Methods for the deprotection of the 2-O-phenacyl and 2-O-(methoxycarbonylmethyl) ethers are described.