Palladium-Catalyzed Direct Oxidative C-H Cross-Coupling Of Azoarenes With Alcohols

Transition metal-catalyzed direct C-H cross-coupling reactions of two organic molecules to form C-C bond are among the most attractive and challenging hot topics in organic chemistry. Especially itis efficient to use palladium as the catalyst. In this kind of reaction, especially much attention has been particularly focused on the regioselective cross-coupling via C-H bond activation with the chelation assistance of a directing group. But there are rare reported examples employed the azo group as a directing group to accelerate the C-H activation/functionalization process.Azo-substituted aryl ketones are important structural motifs of photochemical materials and biosensors. Moreover, these compounds could be easily converted into the corresponding amino- or hydrazino products which are widely utilized in the field of organic synthesis.This essay we describe a convenient Pd-catalyzed direct C-H oxidatvie cross-coupling of azoarenes with no prefunctionalized alcoholds as ideal in situ-generated acylating agents to provide ortho-acylated azoarenes,it is regioselective cross-coupling to use the azo group as a directing group. Azobenzene and benzoyl alcohol were first used as the model substrate to screen the reaction conditions for the optimization condition,the reactions were carried out using azoarene(0.15 mmol) and phenylmethanol( 0.15 mmol) with Pd(OAc)2(10 mol%) in the presence of TBHP(4.0 equiv.) in Ph Cl(2.0 m L) at 80℃ for 30 h under an argon atmosphere, and got the acylated product in 25%-83% yield. The palladium catalyst reacted with azobenzene by chelation-directed C-H activation to form a cyclopalladated intermediate, the palladacyclereacted with the acyl radical which was in situ formed from benzoyl alcohol to generate Pd species. the Pd species underwent reductive elimination to afford the acylation product. This reaction provides a convenient access to ortho-acyl azoarenes under mild conditions in which readily available alcohols were used as the acyl sources.The acylated product undergone intramolecular cyclocoupling reaction to get the corresponding azofluo- renone, which has potential use as a promising industrial dye or nonlinear optical device.