1. N. S. Dixit and C. C. Patel,J. Ind. Chem. Soc., 54, 176 (1977).
2. A. Sreekantan and C. C. Patel,Ind. J. Chem., 16A, 215 (1978).
3. L. Wolff, P. Bock, G. Lorentz and P. Trappe,Annalen., 325, 134 (1902).
4. O. Touster,Org. React., 7, 353 (1953).
5. L. Knorr,Annalen., 236, 80 (1887).