"Ring Opening-Ring Closure" Strategy for the Synthesis of Aryl-C-glycosides

A new "ring-opening-ring closure" strategy for the synthesis of aryl-C-glycosides was described. This strategy exploited the nickel-catalyzed regioselective beta-O elimination of glycals by reactions with various aryl boronic acids or potassium aryltrifluoroborates to yield the ring-opened products, which underwent the Lewis acid, protonic acid, PhSeCl, or NBS mediated ring closure reactions to afford diverse aryl-C-glycosides. After Lewis acids and protonic acids were screened, it was found that, starting from the ring-opened substrates, the Ph3PHBr or Sc(OTf)(3) mediated ring closure reaction provided alpha-or beta-preferred aryl-C-Delta(2,3)-glycosides, respectively. Furthermore, beta-D-phenyl-C-glycosides were successfully prepared via the PhSeCl-mediated cyclization reaction, whereas the alpha-D-phenyl-C-glycoside was obtained via the NBS-mediated cyclization reaction. After removal of the 2-substituted functionalities by Bu3SnH/AIBN, the synthesis of 2-deoxy-aryl-C-glycosides was ultimately realized in a stereoselective manner.