A new route to substituted furocoumarins via copper-catalyzed cyclization between 4-hydroxycoumarins and ketoximes

Abstract

A new route to substituted furocoumarins via copper-catalyzed cyclization between 4-hydroxycoumarins and ketoximes was developed. CuBr₂ exhibited higher activity than other copper salts, affording the desired furocoumarins in high yields. The transformation proceeded readily in the absence of stoichiometric external oxidants. The significance of this synthetic strategy would be (1) the easily available starting materials; (2) low cost catalyst CuBr₂; and (3) being without stoichiometric external oxidants. This protocol is complementary to previous approaches in the synthesis of substituted furocoumarins.