Benzimidazolone — method

A mixture of o-phenylenediamine (2.16 g, 20 mmol) and urea (1.32 g, 22 mmol) in Af,N-dimethylacetamide (0.5 ml) and diethylene glycol (5 ml) contained in a 100 ml Erlenmeyer flask covered with a watch glass is irradiated in a microwave oven at 385 W (2 min) in an efficient fume hood. The mixture is allowed to cool to room temperature, and the precipitate is collected, washed with water (3 ml), acetone (5 ml) and ethanol (5 ml) before recrystallization from ethyl acetate. The yield is 91%, m.p. 308-309°C. 

In a 100ml stainless steel autoclave, o-nitroaniline (2.76g, 20mmol), sulfur (2.57 g, 80 mmol), water (2.0 ml, 110 mmol), ammonium formate (6.30 g, 100 mmol), potassium carbonate (4.14g, 30 mmol) and dimethylacetamide (40 ml) are placed along with a magnetic stirring bar. The reaction is carried out at 180°C for 3h (maximum pressure 10kgcm ). After extraction with 1-butanol, the product (2.52 g, 94%) is recrystallized from 1 1 aqueous methanol. Similarly prepared arc 5-methyl- (27%), 5-methoxy- (36%) and 5-chlorobenzimidazolones (76%), 

Analogous methods lead to benzimidazolethiones when o-phenylene-diamine.s arc treated with carbon disulfide, ihiophosgene, l.l -thiocarbonyldi-imidazolc, thioureas, thiocyanates or potassium ethyl xanthate [123, 126-129]. The reactions with carbon disulfide take place in basic media, e.g. with KOH or pyridine. Again, microwave irradiation offers advantages 1123]. 

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UV spectroscopy method was used to study the acid-base properties of nitroderivatives of benzimidazolones [1194] and benzimidazolthiones [1195], Essential distinctions in the UV spectra of isomers I and II can be used for establishing the alkylation center of corresponding benzimidazolones [1195] and benzimidazolthiones [1196],... 

In view of the observation that A-o-nitrophenyl derivatives of glycine and other a-amino acids could be converted into benzimidazolones by the action of heat, and the assumption that iV-oxides were intermediates in the thermolysis [156], it was thought tliat flash vacuum pyrolysis with a very short reaction time might allow isolation of the IV-oxides. This approach, however, did not turn out to be as synthetically efficient as the base treatment method [97]. Indeed, heating such compounds in sand at 200° C is probably of more use for making benzimidazoles or benzimidazolones [156]. Benzimidazole iV-oxides can be made from acid-catalysed thermal or photochemical reactions of AyV-dialkyl-o-nitroanilincs, but not from purely thermal reactions. 

Ellis KK, Wilke B, Zhang Y, Diver ST (2000) A new method for the synthesis of imidazolidinone- and benzimidazolone-containing [2.2]cyclophanes. Org Lett 2(24) 3785-3788... 

Mamedov VA, Zhukova NA, Beschastnova TN, Syakaev VV, Krivolapov DB, Mironova EV, Zamaletdinova AI, Rizvanov IKh, Latypov ShK (2015) Rearrangement of quinoxalin-2-ones when exposed to enamines generated in situ from ketones and ammonium acetate method for the synthesis of l-(p5urolyl)benzimidazolones. J Org Chem 80(3) 1375-1386. doi 10.1021/ jo502135d... 

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