Synthesis of Dibenzopyranones through Palladium-Catalyzed Directed C-H Activation/Carbonylation of 2-Arylphenols

摘要

The dibenzopyranone scaffold is found in many natural products and biologically active molecules, and was considered as a privileged structure, which is of great importance as intermediate for the synthesis of various pharmaceutically interesting compounds.Traditionally, major methods for the synthesis of dibenzopyranone derivatives include: 1) Baeyer-Villiger oxidation of fluorenone (Scheme 1, path a); 2) lac-tonization of 2-halobiarylcarboxylic acid derivatives; 3) cross-coupling from 2-halobenzaldehydes and o-hydroxy-arylboronic acids, followed by lactonization (path c); 4) intramolecular C—C bond formation of aryl 2-haloben-zoate (path d). Although these present methods exhibited their individual advantages, they generally involved multistep procedures, sometimes harsh reaction conditions, starting materials that are not readily available, and the requirement of prefunctionalization. From the point of view of atom- and process-economical chemistry, to develop an efficient and general synthetic route with less waste is highly desirable. In view of recent advances in C—H bond carbonylation, we envisaged that the dibenzopyranone scaffold might be easily constructed from 2-phenylphenol through palladium-catalyzed C-H activation/carbonylation.