1. J. Ashby and C. C. Cook, Adv. Heterocyclic Chem.,16, 181 (1974).
2. D. S. Breslov, Multi-Sulphur and Sulphur and Oxygen Five-and Six-Membered Heterocycles, J. Wiley and Sons, New York (1966), pp. 864, 1155.
3. E. D. Savin and V. I. Nedel'kin, Khim. Geterotsikl. Soedin., No.8, 1132 (1996).
4. M. Hunt and C. S. Marvel, J. Am. Chem. Soc.57, 1691 (1935).
5. C. Bodea and I. Silberg, Rev. Roumaine Chim.,9, 425 (1964).