1. G. Cauquis, B. Chabaud, and M. Genies, Bull. Soc. Chim. Fr., No. 12, 3487 (1973).
2. T. Jacobs, in: Heterocyclic Compounds, Vol. 2 [Russian translation], Izd. Inostr. Lit., Moscow (1960), p. 88.
3. R. N. Castle, in: Heterocyclic Compounds, Vol. 27, New York-London (1973), p. 321.
4. W. R. McBride and H. W. Kruse, J. Am. Chem. Soc., 79, 572 (1957).
5. G. Cauquis, B. Chabaud, and Y. Gohee, Tetrahedron. Lett., No. 30, 2583 (1977).