Borovkov, V. V.; Evstigneeva, R. P.; Makova, S. Z. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1992 , vol. 28, # 2 p. 142 - 147 Khimiya Geterotsiklicheskikh Soedinenii, 1992 , # 2 p. 176 - 182