Copper-catalyzed Selective Oxidations Of Allylic And Benzylic C-H Bonds

Carbon-hydrogen bonds are widely exists in the organic compounds. It is a more efficient and atom-economic way to introduce the desired functional groups by direct C-H bond functionalization comparing to conventional methods. The direct functionalization of C-H bonds is a long-lasting challenge in modern organic chemistry. Due to the high stability of the C-H bonds, both the activity and the selectivity of C-H bond functionalization reactions are difficult issues. Although remarkable progress has been made in the field of C-H bond activation, the successful catalytic system is limited. These reactions usually use harsh conditions, special catalysts and reagents. And the substrate scopes are limited, and the reactivity and selectivity are low. Therefore, the developments of C-H bond functionalization reactions are very important for both basic research and applications. This article disclosed the copper-catalyzed selective oxidation reactions of allylic and benzylic C-H bonds under mild oxidative conditions. Allylic and benzylic alcohols and their derivatives are synthesed directly and efficiently.A series of nitrogen-containing chiral spiro ligands have been designed and synthesized. By using copper complexes of these chiral ligands, the asymmetric allylic oxidation reaction of cyclic olefin was achieved with high reactivity and up to87%ee enantioselectivity.By using the complexes of copper and chiral spiro bisoxazoline ligands as catalysts, asymmetric allylic oxidation of acyclic olefins has also been developed. The oxidation of various acyclic olefins was realized with excellent regioselectivity (>20:1in most cases) and up to67%ee under mild reaction conditions, which represents one of the best results for the enantioselective allylic oxidation of acyclic olefins.This research provides a new way for the synthesis of chiral allyl alcohol and its derivatives directly from feedstocks.In addition, a selective oxidation of benzylic C-H bonds to C(sp3)-O bonds catalyzed by copper complexes of quinoline-imine ligands was developed with high selectivity under mild reaction conditions, which converted benzylic methylenes directly into benzylic alcohols and esters by means of direct C-H bond functionalization.In summary, we have developed copper-catalyzed selective oxidations of allylic and benzylic C-H bonds. The reactions are highly selective in the synthesis of allylic and benzylic alcohols and their derivatives. The results achieved in this study are important not only for basic research, but also have potential applications.