Activation Coupling Of C-H Bond By Superacid-catalyzed And Synthesis Of Quaternaryα-hydroxy Phosphonates

The present paper reports two transition-metal-free oxidative couplingreactions for direct C-H functionalization: ① oxidative coupling cyclization ofquinones by superacids catalysis; ② α-hydroxylation reactions of phosphonates withCs2CO3 serve as highly efficient catalyst.(1) Most oxidative coupling reactions have been achieved using transition-metalcatalysts; Furthermore, most of the oxidative C-C 、 C-H 、 C-X functionalizationreactions have been focused on the aromatic, vinylic C-H and activated C(sp3)-Hbonds, whereas the direct oxidative C-H transformation of quinones has rarely beenreported. Herein, we present the transition-metal-free direct oxidative couplingcyclization C-H transformation of quinones for the synthesis oftetrahydrobenzodifuran in the superacid-catalyzed superelectrophilic reaction system.The acidity of catalysts would need to show strong enough, and a suite of catalystsuch as trifluoroacetic acid, solid superacid Ti O2/SO42-and Al Cl3/Cl-led to a decreasedyield and no reaction occurred., thus indicating that the choice of catalyst is essential.(2) α-Hydroxy phosphonates one important type of organic phosphoriccompounds, possess intriguing biological activities and have gained widespreadapplications in many areas, including biological and pharmaceutical industries, due totheir physical and structural similarity to biologically important phosphate esters.Therefore, although a significant number of transition-metal-catalyzed C-Hhydroxylation reactions have been developed, practical and efficient C-Hhydroxylation reactions with molecular oxygen as the oxidant and oxygen source arestill desirable.