Ibatullin, U. G.; Pavlov, Yu. V.; Safarov, M. G. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1989 , vol. 25, # 10 p. 1107 - 1109 Khimiya Geterotsiklicheskikh Soedinenii, 1989 , # 10 p. 1326 - 1328