Synthesis of Neoflavenes by a Palladium-Catalyzed Cross-Coupling Reaction of 4-Trifluoromethylsulfonyloxy-2 H -Chromenes with Arylboronic Acids

Under anhydrous conditions, 4-phenyl-2H-chromenes were obtained in excellent yields by a cross-coupling reaction of 4-trifluoromethylsulfonyloxy-2H-chromenes with arylboronic acids, except for o-methoxyphenylboronic acid, in the presence of K2CO3 and several palladium catalysts. Although copper(I) iodide, used as a co-catalyst, showed no effect on this reaction, it was confirmed to act in the case of the coupling reaction of 4-trifluoromethylsulfonyloxy-2H-chromene with tributylphenyltin, instead of phenylboronic acid, in the presence of [Pd(PPh3)4].