Studies of imidazo[1,2-a]benzimidazole derivatives. 21. Synthesis of haloketones in the imidazo[1,2-a] benzimidazole series

Methods for the synthesis of imidazo1,2-a]benzimidazole haloketone derivatives have been investigated. It has been found that -bromoketone derivatives of this heterocycle can be prepared either by bromination of 3-acylimidazo1,2-a]benz-imidazoles with bromine in glacial acetic acid or by acylation of 3-unsubstituted imidazo1,2-a]benzimidazoles with haloanhydride derivatives of -bromoalkanoic acids. Treatment of imidazo1,2-a]benzimidazoles with 3-chloropropionyl chloride results in the formation of imidazo1,2-a]benzimidazolyl-3-propionyl chloride and bis(imidazo1,2-a]benzimidazolyl)propan-3-one derivatives as side products. Reaction of 2-phenylimidazo1,2-a]benzimidazoles with 3-bromopropionic acid in polyphosphoric acid gives benzocyclohepten5,6:4,5]imidazo1,2-a]benzimidazole derivatives.For Communication 20, see 1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 339–345, March, 1986.