Gel'mont, M. M.; Akulin, Yu. I.; Strelets, B. Kh.; Efros, L. S. Chemistry of Heterocyclic Compounds (New York, NY, United States), 1983 , vol. 19, # 7 p. 786 - 792 Khimiya Geterotsiklicheskikh Soedinenii, 1983 , vol. 19, # 7 p. 975 - 981