One-Pot Synthesis of Monofluoromethoxy Arenes from Aryl Halides, Arylboronic Acids and Arenes

Fluorine-containing compounds have been widely used in the fields of pharmaceuticals, agrochemicals and functional materials, mainly due to the well-known "fluorine effect" of the fluoroalkyl groups on the physical, chemical and biological properties of molecules. Tri- and difluoromethyl ethers play an important role in many medicinally compounds. Among various fluorinated moieties, ORf-containing groups have attracted much more attention very recently owing to the impressive conformational changes and maximal shifts in electron distribution brought by fluorine. The alpha-fluorine substitution of ethers shortens and strengthens the C-O bond and thus improves the in vivo oxidative stability of the ether moiety of a drug. Over the past few decades, there are some reliable ways on accessing trifluoromethyl ethers and difluomethyl ethers. Considering the importance of synthesis of monofluoromethoxy arenes and the substrate limitation (phenols or alcohols) of current state, a method was developed to access monofluoromethoxy arenes from aryl halides, arylboronic acids and arenes via a one-pot synthesis. Phenols can be prepared by the hydroxylation of aryl halides catalyzed by transition-metal complexes. In this work, a new strategy was envisioned a two-step sequence for the conversion of aryl halides to monofluoromethoxy arenes based on the palladium-catalyzed conversion of aryl phenols and in situ conversion of the resulting phenoxides with monofluoromethylating reagents. The investigation began with optimization of the conversion of 1-chloro-4-methoxy-benzene. The approach was achieved by using Pd-2(dba)(3) (2 mol%) as the catalyst under an inert atmosphere, di-tertbuty1(2',4',6'-triisopropyl-[1,1'-biphenyl]-2-yl)phosphane (8 mol%) as the ligand, KOH (1 equiv.) as the nucleophile, and 1,4-dioxane/H2O (V : V=5 : 3) as the solvent. Further monofluoromethylation used fluoromethyl iodide (2 equiv.) as the monofluoromethylating reagent and CH3CN as the co-solvent. Finally, the desired product was obtained in 82% yield. Therefore, this method was also applied to drugs, for example, Loratadine could be converted to the corresponding product (2o) in 53% yield and Fenofibrate, reacting to form the monofluoromethoxy arenes (2p) in modest yield. One-pot method to access aryl monofluoromethyl ethers from arylboronic acids and arenes were also under consideration and the yields were objective.