Metal-free direct C–H phosphonation of N-heterocycles with diphenylphosphine oxides under mild conditions

Abstract

Herein, metal-free phosphonation of N-heterocycles with diphenylphosphine oxides, promoted by easily available 1,5-diazabicyclo[5,4,0]undec-5-ene (DBU) in dimethyl carbonate (DMC) as a green solvent under an air atmosphere, is presented. This simple method can accommodate 1,2,4-triazine-3,5(2H,4H)-diones, quinoxalin-2(1H)-ones, quinoxalines and pyrazinones with diverse substituted diphenylphosphine oxides, delivering distinctive monophosphonated N-heterocycles with a broad functional group tolerance, and the transformations are also viable for post-modification of bioactive and pharmaceutical molecules. In addition to the sustainable feature of being metal- and photocatalyst-free and utilization of ambient air as an oxidant, this method efficiently achieves the gram-scale transformation, and the product was isolated through extraction and filtration, rather than column chromatography.