The stereoselective introduction of glycosidic bonds is of paramount importance to oligosaccharide synthesis. Among the various chemical strategies to steer stereoselectivity, participation by either neighboring or distal acyl groups is used particularly often. Recently, the use of the 2,2-dimethyl-2-(ortho-nitrophenyl)acetyl (DMNPA) protection group was shown to offer enhanced stereoselective steering compared to other acyl groups. Here, we investigate the origin of the stereoselectivity induced by the DMNPA group through systematic glycosylation reactions and infrared ion spectroscopy (IRIS) combined with techniques such as isotopic labeling of the anomeric center and isomer population analysis. Our study indicates that the origin of the DMNPA stereoselectivity does not lie in the direct participation of the nitro moiety but in the formation of a dioxolenium ion that is strongly stabilized by the nitro group.

中文翻译：

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通过 2,2-二甲基-2-(邻硝基苯基)乙酰基 (DMNPA) 保护基团的“双重参与”对 1,2-顺-葡萄糖基化的葡萄糖基二氧代鎓离子进行稳定化

糖苷键的立体选择性引入对寡糖合成至关重要。在控制立体选择性的各种化学策略中，特别经常使用相邻或远端酰基的参与。最近，使用2,2-二甲基-2-(邻与其他酰基相比，-硝基苯基）乙酰基（DMNPA）保护基团显示出增强的立体选择性转向。在这里，我们通过系统糖基化反应和红外离子光谱 (IRIS) 结合异头中心的同位素标记和异构体群体分析等技术，研究 DMNPA 基团诱导的立体选择性的起源。我们的研究表明，DMNPA 立体选择性的起源并不在于硝基部分的直接参与，而是在于形成由硝基强烈稳定的二氧杂鎓离子。