Photocatalyzed Decarboxylative Thio(seleno)etherification of Redox-Active Uronates Enables Synthesis of Rare Sugar Thio(seleno)glycosides

Rare sugar-based thio(seleno)glycosides are synthetically and biologically important yet challenging-to-prepare synthons. We here present a novel approach to such constructs from readily available <i>C</i>-glycosides with photocatalyzed decarboxylative thio(seleno)etherification of redox-active uronates as the key transformation following a C1-to-C5 switch strategy. This protocol tolerates diverse substrates and various protecting groups, stereoselectively affording the desirable thio(seleno)glycosides in moderate-to-high yields. The power of this method is demonstrated by the successful assembly of a 1,7-<i>S</i>-linked trisaccharide composed of α-d-<i>ido</i>-heptopyranosyl units.