Boiko, I. I.; Dergunova, M. E.; Boiko, T. N. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1987 , vol. 23, # 11 p. 1169 - 1171 Khimiya Geterotsiklicheskikh Soedinenii, 1987 , # 11 p. 1467 - 1469