Easton,N.R. et al.
Journal of Organic Chemistry, 1964 , vol. 29, p. 1851 - 1855

Tsoi, L.A.; Rozhnov, V.B.; Rabanyuk, N.N.
Chemistry of Heterocyclic Compounds (New York, NY, United States), 1983 , p. 835 - 838
Khimiya Geterotsiklicheskikh Soedinenii, 1983 , vol. 19, # 8 p. 1044 - 1047