1. Wennerberg AN (1967) US Pat. 3.360.449; Chem Abstr 68:77942
2. Lyashenko LV, Gorokhavatskii YB (1969) Dokl Akad Nauk SSSR 186:1125
3. Schwab G-M, Steinbach F, Noller H, Venugopalan M (1964) Z Naturforsch 19a:45
4. Formenti M, Juillet F, Teichner SJ (1970) C R Acad Sci Paris 270:138
5. Roth W (1978) Hoechst AG, Frankfurt, private communication