Lozanova, Kh.; Simov, D.; Kalcheva, V. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1987 , vol. 23, # 9 p. 1024 - 1026 Khimiya Geterotsiklicheskikh Soedinenii, 1987 , # 9 p. 1277 - 1279