Study On Silver-Catalyzed C(sp~2)-H Functionalization/C-O Cyclization Reaction At Room Temperature

In Organic molecules, C-H bond is ubiquitous. It can form C-C bond、C-S bond、 C-O bond、C-N bond, using directing hydrocarbon activation, so it provides a method with atom economy for synthesizing many useful compounds. But C-H functionalization is not easy because of the high bond energy. At the same time, it has the poor regioselectivity because of the richness in molecules. Therefore, developing an efficient process to form fundamental building block of a wide variety of value compounds, it remain to be achieved.The dibenzopyranone and its derivatives exist in many natural and biologically active products, they are important as intermediate for synthesizing of various pharmaceutically interesting compounds. So, dibenzopyranone is a kind of advantage construction, especially in pharmaceutical sciences.Through many literature researches, it is rare to use directing C-H functionalization to form C-O bond, especially utilizing other metal as catalyzer instead of palladium. In our text, we develop a method of a catalytic C(sp2)-H functionalization/C-O cyclization reaction with 2-methylbenzoic acid and its derivatives utilizing silver as catalyst to synthesize the structure of dibenzopyranone. It proceeds at room temperature and normal pressure with AgNO3 as catalyst, (NH4)2S2O8 as oxidant, CH2Cl2/H2O(1:1, v:v) as solvent. The present method exhibits good functional-group compatibility, such as unprotected OH group and terminal alkene tolerated to some extent. Various products of lactones are obtained in good to excellent yields. Compared to palladium-catalyzed, the reaction has good economy because palladium is not only expensive but also generally needs ligands to improve its activity, which increases the reaction cost; If used Cu, the reaction is relatively harsh, decreasing the functional-group compatibility.In order to further research the role of the catalytic C(Sp2)-H functionalization/C-O cyclization reaction in organic synthesis, we proceed gram-scale reactions, acquiring excellent yields. Next, we have chemoselectivity reaction. In addition, we study the kinetic isotope effect of this reaction, and also based the previous reports and the above mechanistic investigation, we support a possible mechanism, namely radical mechanism.