Ershov, L. V.; Kiselev, S. S.; Granik, V. G. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1984 , vol. 20, # 4 p. 439 - 443 Khimiya Geterotsiklicheskikh Soedinenii, 1984 , vol. 20, # 4 p. 538 - 542