1. A. F. Pozharskii, Theoretical Foundations of the Chemistry of Heterocycles [in Russian], Khimiya, Moscow (1985), p.257.
2. O. N. Chupakhin, V. N. Charushin, and H. van der Plas, Nucleophilic Aromatic Substitution of Hydrogen, Academic Press, San Diego (1994), p.127.
3. O. N. Chupakhin, V. N. Charushin, and H. van der Plas, Tetrahedron, 44, 1 (1988).
4. S. Skonieczny, Heterocycles, 6, 987 (1977).
5. J. Chiron and J. P. Galy, Synthesis, 313 (2004).