Kottenhahn
Justus Liebigs Annalen der Chemie, 1891 , vol. 264, p. 174

Chemistry of Heterocyclic Compounds (New York, NY, United States), , vol. 21, # 4 p. 392 - 396
Khimiya Geterotsiklicheskikh Soedinenii, , vol. 21, # 4 p. 474 - 478

Tolstaya, T. P.; Egorova, L. D.; Lisichkina, I. N.
Chemistry of Heterocyclic Compounds (New York, NY, United States), 1985 , vol. 21, # 4 p. 392 - 396
Khimiya Geterotsiklicheskikh Soedinenii, 1985 , vol. 21, # 4 p. 474 - 478

Valette
Bulletin de la Societe Chimique de France, 1930 , vol. <4>47, p. 289,299

Kottenhahn Justus Liebigs Annalen der Chemie, 1891 ,  vol. 264, p. 174