1. Schmidt, H. W., Zacharias, G., Junek, H., Synthesis1980, 471.
2. Middleton, W. J., US-Pat. 2,794,803 (1957); C.A.52, 2933 (1958).
3. Little, E. L., Jr., Middleton, W. J., Coffman, D. D., Engelhardt, V. A., Sausen, G. N., J. Amer. Chem. Soc.80, 2832 (1958).
4. Schmidt, H. W., Junek, H., Mh. Chem.108, 895 (1977).
5. Johnson, L. F., Jankowski, W. C., Carbon 13-NMR Spectra, S. 109, New York: Wiley.