Ru3(CO)12 is a very efficient catalyst for the deoxygenation of 2-nitro-N-(phenylmethylene) benzeneamine derivatives to give the corresponding 2-substituted benzimidazoles, at 220-degrees-C and 50 bar of carbon monoxide. Main byproducts are the corresponding amines. The same benzimidazoles are also obtained starting from o-nitroaniline and the corresponding aldehyde. When N-(2-nitrophenyl)methylene benzeneamine derivatives are used as substrates, the reaction changes dramatically and only traces of the corresponding heterocyclic compounds are obtained, although complete conversion of the starting nitro compounds is achieved.
Microwave-assisted Cadogan reaction for the synthesis of 2-aryl-2<i>H</i>-indazoles, 2-aryl-1<i>H</i>-benzimidazoles, 2-carbonylindoles, carbazole, and phenazine
mixed with triethylphosphite or triphenylphosphine and irradiated with microwaves for several minutes at a specific power to give the desired products. The indazoles were prepared by irradiating N‐(2‐nitrobenzylidene) anilines with triethylphosphite at 200 W for 12–14 min to give 85–92% product yields. Irradiation of the mixture of N‐benzylidene‐2‐nitroanilines and triphenylphosphine at 200 W for