Russkikh, V. S.; Abashev, G. G.
Chemistry of Heterocyclic Compounds (New York, NY, United States), 1987 , vol. 23, # 11 p. 1183 - 1185
Khimiya Geterotsiklicheskikh Soedinenii, 1987 , # 11 p. 1483 - 1485

Mueller, Harald; Ueba, Yoshinobu
Bulletin of the Chemical Society of Japan, 1993 , vol. 66, # 6 p. 1773 - 1777