Base‐Promoted Glycosylation Allows Protecting Group‐Free and Stereoselective O‐Glycosylation of Carboxylic Acids**

Abstract

Here we report a simple and general method to achieve fully unprotected, stereoselective glycosylation of carboxylic acids, employing bench‐stable allyl glycosyl sulfones as donors. Running the glycosylation reaction under basic conditions was crucial for the efficiencies and selectivities. Both the donor activation stage and the glycosidic bond forming stage of the process are compatible with free hydroxyl groups, thereby allowing for the use of fully unprotected glycosyl donors. This transformation is stereoconvergent, occurs under mild and metal‐free conditions at ambient temperature with visible light (455 nm) irradiation, and displays remarkable scope with respect to both reaction partners. Many natural products and commercial drugs, including an acid derived from the complex anticancer agent taxol, were efficiently glycosylated. Experimental studies provide insights into the origin of the stereochemical outcome.

Stereoselective synthesis of α-glycosyl azides: allyl glycosyl sulfones as radical precursors

“…Our group has been interested in the research of glycosylation reactions and developed a range of glycosyl donors as radical precursors to generate glycosyl radicals, such as glycosyl sulfoxides, 21,22 glycosyl sulfides, 23 glycosyl sulfinates 24,25 and allyl glycosyl sulfone. 26–29 These donors can be activated under mild conditions, successfully making O -, C -, or S -glycosides with great generality and stereoselectivity. Based on our previous work, we report here a versatile and mild approach that employs bench-stable and readily accessible allyl glycosyl sulfones 5 as glycosyl donors to provide α-glycosyl azides 3 (Scheme 1c).…”

Polarity-Matched Initiation of Radical-Polar Crossover Reactions for the Synthesis of C-Allyl Glycosides with gem-Difluoroalkene Groups

“…Our team has made significant strides in the realm of glycosyl radical reactions. We developed a series of bench-stable sulfone-type glycosyl donors 8 and successfully applied them to the construction of aryl and heteroaryl glycosides. Based on our previous study, we introduce here an RPC process for the synthesis of gem -difluoroalkene sugar conjugates using sulfone-type glycosyl donors (Scheme c), aiming to broaden the application of RPC in synthetic glycochemistry.…”