Skvortsov, I. M.; Astakhova, L. N. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1987 , vol. 23, # 11 p. 1189 - 1191 Khimiya Geterotsiklicheskikh Soedinenii, 1987 , # 11 p. 1489 - 1491