Arenes selectively nitrated at meta position

Nitroarenes are important in medicinal chemistry and materials science applications and as synthetic precursors. Chemists typically make them by adding nitro groups at positions ortho or para to electron-donating directing groups on arene starting materials. Ao Zhang of Shanghai Institute of Materia Medica and coworkers now demonstrate that nitro groups can be added to arenes at the meta position (J. Am. Chem. Soc. 2016, DOI: 10.1021/jacs.6b03402). It’s the first use of directing-group-assisted direct C–H functionalization to form C–N bonds. Using Ru₃(CO)₁₂ as the catalyst and Cu(NO₃)₂·3H₂O as the nitro source, the researchers were able to nitrate a variety of N-heterocycle- or oximido-substituted arenes at the meta position exclusively. In the reaction, the catalyst and substrate combine to form an octahedral ruthenium intermediate. A nitro group adds to the intermediate at a position para to a ruthenium-carbon bond but meta to the substituent. Release of the nitrated substrate from the complex then yields the meta derivative. Zhang and coworkers used the reaction to make drug intermediates, clinical candidate precursors, and marketed drugs, and reaction products can serve as intermediates for further transformations.