Levchenko, N. K.; Segal', G. M.; Torgov, I. V. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1981 , vol. 17, # 3 p. 251 - 256 Khimiya Geterotsiklicheskikh Soedinenii, 1981 , vol. 17, # 3 p. 347 - 351