Iovel', I. G.; Gol'dberg, Yu. Sh.; Shimanskaya, M. V. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1989 , vol. 25, # 6 p. 613 - 616 Khimiya Geterotsiklicheskikh Soedinenii, 1989 , vol. 25, # 6 p. 746 - 749