Highly ( Z)-Diastereoselective Synthesis of Trifluoromethylated exo-Glycals via Photoredox and Copper Catalysis.

Highly ( Z)-diastereoselective approaches for the synthesis of trifluoromethylated exo-glycals by copper and photoredox catalysis are described. These complementary reactions are applicable to a wide range of methylene exo-glycals generated from the corresponding pyranoses and furanoses and give trifluoromethylated compounds under mild conditions in moderate to good yields. DFT calculations have allowed a rationalization of the observed ( Z)-stereoselectivity.