1. A. Angeli,Gazz. Chim. Ital. 46 II (1916) 279,48 II (1918) 21.
2. G. P. Gardini,Adv. Heterocycl. Chem. 15 (1973) 67.
3. R. Steude, PhD thesis July 1933, Technische Hochschule, Munich.
4. A. Dall'Olio, Y. Dascola, V. Varacca and V. Bocchi,C. R. Acad. Sci., Ser. C,267 (1968) 433.
5. A. F. Diaz and J. I. Castillo,J. Chem. Soc. Chem. Commun. (1980) 397.