1. L. I. Belen'kii, E. P. Zakbarov, M. A. Kalik, V. P. Lirvinov, F. M. Stoyanovich, S. Z. Taits, and B. P. Fabrichnyi New Trends in the Chemistry of Thiophene, Ya. L. Gol'dfarb (ed.) [in Russian]. Nauka, Moscow (1976).
2. I. Magnasco and F. Ode, Scientia,31, 5 (1964).
3. A. Scancke and P. A. Scancke, Acta Chem. Scand.,24, 23 (1970).
4. M. Dewar and N. Trinajsti?, J. Am. Chem. Soc.,92, 1453 (1970).
5. F. Momicchioli and A. Rastelli, J. Mol. Spectrosc.,22, 210 (1967).