1. E. Havinga and J. Cornelisse,Pure Appl. Chem.,47, 1 (1976).
2. J. den Heijer, Thesis, Leiden (1977).
3. H. C. H. A. van Riel, Thesis, Leiden (1977).
4. J. J. Tamminga, Thesis, Leiden, to be published.
5. A. V. El’tsov, O. V. Kul’bitskaya, and A. N. Frolov,J. Org. Chem. USSR,8, 78 (1972).