1. Presented in part at the National Congress of Chemistry, Bucharest, 11–14 September, 1978.
2. M. D. Gheorghiu, L. Parvulescu, C. Draghici and M. Elian, Abstract No. 5-A-84.
3. R. B. Woodward and R. Hoffmann, The Conservation of Orbital Symmetry. Academic Press, New York
4. The Conservation of Orbital Symmetry;Woodward,1970
5. Ketene cycloadditions