This report is concerned not only with the syntheses of new ring systems and the preparation of derivatives of known rings but also with new types of catalysts based upon, e.g., nickel, iron, molybdenum, manganese, and palladium. The broad applicability of the methylene insertion reaction as a method for identifying monoand di-methyl-substituted eight-, ten-, and twelve-,membered rings is also demonstrated. A further section is concerned with the possible mechanism of C-C bond formation in transition metal complexes; several earlier suggestions have been revised in the light of new experimental data. In addition, experimental results are discussed which indicate that the reactivity and selectivity of the complexes formed by the nickel-ligand catalyst and olefins or alkynes depend upon the structure of the ligands. A number of interesting syntheses have likewise been carried out starting from cis-1,2-divinyIcyclobutane. A few examples are shown in eq. (62)['641. 0s: 1 + COOR -COOH J COOR ROOC COOR COOR COOR 0 I wish to express tit!' thanks, also on behalf ofmy co-workers, to the Director of the Max-Planck-Institut f iir Kohlenforsckung ProJ Dr. G. Wilke for his support of our work and for many useful suggestions. In particular I gratefully acknowledge continuingfinancial and academic support even after my acceptance of a position at the Gesamtkochsckule Essen. I also wish to acknowledge the friendly assistance