Thiol-ene coupling (TEC) reactions emerged as one of the most useful processes for coupling different molecular units under reaction mild conditions. However, TEC reactions involving weak CH bonds (allylic and benzylic fragments) are difficult to run and often low yielding. Mechanistic studies demonstrate that hydrogen-atom transfer processes at allylic and benzylic positions are responsible for the lack of efficiency of the radical-chain process. These competing reactions cannot be prevented, but reported herein is a method to repair the chain process by running the reaction in the presence of triethylborane and catechol. Under these reaction conditions, a unique repair mechanism leads to an efficient chain reaction, which is demonstrated with a broad range of anomeric O-allyl sugar derivatives including mono-, di-, and tetrasaccharides bearing various functionalities and protecting groups.

The development of general and expedient methodologies for the preparation of orthogonally protected glycoside building blocks is essential for the efficient synthesis of complex oligosaccharides. Herein, we describe a new approach that uses copper(II) triflate as a versatile catalyst for the onepot preparation of orthogonal protected thio-and O-glycosides from the corresponding unprotected counterparts. The conditions are mild, easy to handle and applicable to two and three one-pot tandem transformations, which include arylidene acetalation, esterification, regioselective reductive acetal ring opening, glycosylation and silylation processes.

A general and efficient chromatography-free ionic-liquid-supported "catch-and-release" strategy for oligosaccharide synthesis (ICROS) is reported. The methodology is compatible with current glycosylation strategies and amenable to protecting group manipulations. A series of β-(1→6) and β-(1→2)-linked glycan structures have been prepared to showcase the versatility of the strategy.