1. I. F. Tishchenkova, L. E. Kholodov, and V. G. Yashunskii, Khim.-Farmats. Zh., No. 12, 7 (1968).
2. R. Elderfield and É. Lozin, in: Heterocyclic Compounds, Wiley (1950?1967).
3. J. H. Markgraf and W. Scott, Chem. Commun., 296 (1967).
4. J. H. Markgraf, R. J. Katt, W. Scott, and R. N. Shefrin, J. Org. Chem., 34, 4131 (1969).
5. W. Borsche, Ann., 377, 120 (1910).