The Technical Synthesis of 1,5,9-Cyclododecatriene Revisited: Surprising By-products from a Venerable Industrial Process.

The synthesis of 1,5,9-cyclododecatriene by selective trimerization of butadiene catalyzed by TiCl4 and ethyl aluminium sesquichloride has been commercially used since 1965. Although thoroughly investigated, not all details of the mechanism are completely understood. The recent development of a new process to produce cyclododecanone by oxidizing 1,5,9-cyclododecatriene with N2O has led to the serendipitous discovery of an array of hitherto unknown by-products, formed in the trimerization of butadiene: eleven tricyclic C12H20 and one tetracyclic C12H18 hydrocarbon, three of which had never been described before. The identification of these by-products became possible by using a combination of chemical enrichment, high-resolution distillation, 13C-2D-INADEQUATE NMR and comparison with ab initio calculated spectra, thus demonstrating the power of these combined techniques. The identification of these by-products contributes to a better understanding of the mechanism of this centrally important reaction.