Protecting group-free and 1,2-trans selective glycosylation of carboxylic acids

Here we report a simple and general method to achieve fully unprotected, 1,2-trans- (-) selective glycosylation of carboxylic acids employing allyl glycosyl sulfones as donors. This reaction occurs under ambient temperature and basic conditions under visible light irradiation. The method is stereoconvergent, as allyl glycosyl sulfone donors pass through glycosyl radical intermediates, en route to glycosyl electrophiles. Thanks to the unique radical-based donor activation mechanism, fully unprotected glycosyl donors can be used directly. This transformation displays remarkable substrate scope with respect to both reaction partners. To illustrate its generality and potential utility, a number of commercial drugs and an acid derived from anticancer agent paclitaxel were efficiently glycosylated. Experimental and theoretical studies provide insights into the origin of the stereochemical outcome of this reaction.