The glycosylation reaction, which is key for the studies on glycoscience, is challenging due to its complexity and intrinsic side reactions. Thioglycoside is one of the most widely used glycosyl donors in the synthesis of complex oligosaccharides. However, one of the challenges is its side reactions, which lower its yield and limits its efficiency, thereby requiring considerable effort in the optimization process. Herein, we reported a multifaceted experimental approach that reveals the behaviors of side reactions, such as the intermolecular thioaglycon transformation and Nglycosyl succinimides, via the glycosyl intermediate. Our mechanistic proposal was supported by low temperature NMR studies that can further be mapped by utilizing relative reactivity values. Accordingly, we also presented our findings to suppress the generation of side products in solving this particular problem for achieving high-yield glycosylation reactions.
A multifunctional O-phenyl thiocarbonyl (O(CS)OPh)
group was introduced in glycosylation reactions. This auxiliary group
exhibits three features (1) C6-long-range participation
effect, (2) relay activation, and (3) switchable promoter-controlled
carbonylation, which enables the facile synthesis of both 6-deoxy
glucoside and 6-alcohol glucoside. In addition, we successfully quantified
the extent of the C6-acyl participation effect and
developed its application toward the α-trisaccharide motif.
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