Kalcheva, V. B.; Peshakova, L. S.; Simov, D. A. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1984 , vol. 20, # 11 p. 1210 - 1213 Khimiya Geterotsiklicheskikh Soedinenii, 1984 , # 11 p. 1467 - 1471