Bumagin, N. A.; Kalinovskii, I. O.; Beletskaya, I. P. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1983 , vol. 19, # 11 p. 1159 - 1162 Khimiya Geterotsiklicheskikh Soedinenii, 1983 , # 11 p. 1467 - 1470