Synthesis Of Fluorenone Derivatives By Catalytic Oxidation Of Water-soluble Metal Complexes

Fluorenone derivatives stand as significant structural motifs in many fields.For example,fluorenones derivatives are widely used in the field of OLED as optical materials;In biomedical science,fluorenone derivatives serve as important intermediates which can be used to synthesize many kinds of drug molecules,such as anticancer,antispasmodic agents and cross-nerve inhibitors,etc;In the field of polymer materials,fluorenone derivatives are often used as additives for functional polymer polyester materials,which can significantly improve the properties of resins.Among those methods to synthesize fluorenone derivatives,the most commonly used one is the oxidation of fluorene to fluorenone compounds.Most oxidation strategies require noble metal as catalyst or hypervalent iodine or peroxide as oxidant.Moreover,reactions need to be carried out in organic solvents,resulting in increasing product cost and pollution to the environment.These drawbacks impede their applications in industrial production.With the development of the concept of green chemistry,chemical research develops toward the environment-friendly and sustainable process.Reducing the use of harmful substances from the source to reduce waste generation is one of the strategies to achieve green chemistry.Molecular oxygen has obvious advantages over other oxidants due to its natural abundance and low price.Also,using oxygen as oxidant could avoid over-oxidation and its only byproduct is water.Compared with other organic solvents,water is environmentally benign,and may simply the workup procedure Therefore,we try to synthesize the fluorenone derivatives with molecular oxygen as the oxidizing agent and water as the reaction solvent.In order to increase the solubility of the catalyst and substrates,threemodifiedN-ligandsbaseonpyridine,bipyridineand1-10-phenanthroline by introducing PEG（polyethoxy）chains to aromatic ring.The oxidation of fluorenone was carried out in the presence of water-soluble ligands with copper as catalyst.Through the screening of metal catalyst,ligand,base and temperature for the reaction,the optimum reaction conditions for the synthesis of fluorenone derivatives in aqueous medium were determined.The optimum reaction conditions were as follows:0.5 mol%CuCl₂·2H₂O as catalyst.0.5 mol%L1 ligand,7.0 equiv.NaOH as base,water was used as solvent,and reaction was carried out at50 ^oC,0.1 MPa O₂.This condition is suitable for a wide range of substrates.A total of12 fluorenones derivatives have been obtained.In this paper,the melting point,LR-MS or HRMS,¹H NMR and ¹³C NMR of the PEG-functionalized N-ligands and fluorenone derivatives have been measured and characterized.In conclusion,a new and benign method for the synthesis of fluorenone derivatives has been developed.