1. Kirsch, G., Neef, G., Laurent, H., Wiechert, R., Beier, S., Elger, W., and Bull, J.R., FRG Patent Appl. no. DE 3838779 A1, 1990
2. Chem. Abstr., 1990, vol. 113, no. 231776.
3. Laurent, H., Esperling, P., Krattenmacher, R., and Elger, W., FRG Patent Appl. no. 4114635 A1, 1992
4. Chem. Abstr., 1993, vol. 118, no. 124872.
5. Kirsch, G., Neef, G., Laurent, H., Wiechert, R., Bull, J.R., Elger, W., and Beier, S., FRG Patent Appl. no. 3939894, 1991