The Transition Metal-catalyzed N-Heterocyclization. A Reductive Transformation of Aminonitroarenes and Dinitroarenes into Phenanthroline Derivatives Using Aliphatic Aldehydes under Carbon Monoxide Pressure

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Abstract
The Catalytic N-heterocyclization of aminoarenes and dinitroarenes using aliphatic n-C3–C5 aldehydes was carried out at 180 °C under the pressure of carbon monoxide (70 atm at room temperature) in the presence of RhCl(PPh3)3 and PdCl2 as a binary catalyst system. The reaction of p-nitroaniline with propanal, butanal, and pentanal gave 3,8-diethyl-2,9-dimethyl-4,7-phenanthroline, 2,9-diethyl-3,8-dipropyl-4,7-phenanthroline, and 3,8-dibutyl-2,9-dipropyl-4,7-phenantroline in 43, 57, and 54% yields respectively. On the other hand, m-nitroaniline and o-nitroaniline gave 1,7-phenanthroline and imidazole derivatives in rather low yields (21 and 24%) under the reaction conditions employed.