Triple Role of Proton Sponge (DMAN) in the Palladium-Catalyzed Direct Stereoselective Synthesis of <i>C</i>‑Aryl Glycosides from Glycals

The triple role of 1,8-bis(dimethylamino)naphthalene (proton sponge) as a reductant, ligand precursor, and organic base in the palladium-catalyzed Heck-type coupling reaction of glycals with aryl iodides affords the rapid and stereoselective synthesis of 2′,3′-unsaturated α-C-aryl glycosides in excellent yields. The role of the proton sponge in reducing palladium(II) to (0) has been studied using cyclic voltammetry, UV–vis, HRMS, and other spectroscopic techniques. This is the first example of a palladium proton sponge complex utilized in coupling reactions. The method is observed to be tolerant of various functional groups, as demonstrated by the huge substrate scope. Moreover, the 2′,3′-unsaturated α-C-aryl glycosides were also converted to 3-keto-β-C-glycosides under sterically hindered pyridinium salt catalysis via a ring-opening and -closing mechanism