1. R. Fusco, in: The Chemistry of Heterocyclic Compounds, Vol. 22, Intersci. New York-London-Sydney (1967), p. 93.
2. R. Hüttel, F. Büchele, and P. Jochum, Chem. Ber., 88, 1577 (1955).
3. G. T. Morgan and J. Reilly, J. Chem. Soc., 105, 435 (1914).
4. G. T. Morgan and J. Ackerman, J. Chem. Soc., 123, 1308 (1923).
5. S. F. Torf, N. I. Kudryashova, N. V. Khromov-Borisov, and T. I. Mikhailova, Zh. Obshch. Khim., 32, 1740 (1962).