Nasakin, O E.; Alekseev, V. V.; Promonenkov, V. K.; Bulai, A. Kh.; Sil'vestrova, S. Yu. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1981 , vol. 17, # 6 p. 541 - 543 Khimiya Geterotsiklicheskikh Soedinenii, 1981 , # 6 p. 744 - 746