Kost, A. N.; Yurovskaya, M. A.; Vyazgin, A. S.; Afanas'ev, A. Z. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1980 , p. 921 - 925 Khimiya Geterotsiklicheskikh Soedinenii, 1980 , vol. 16, # 9 p. 1222 - 1226