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

The synthesis of 1,5,9-cyclododecatriene by selective trimerization of butadiene catalyzed by TiCl and ethylaluminum 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 involving oxidation of 1,5,9-cyclododecatriene with NO has led to the serendipitous discovery of an array of hitherto unknown byproducts, formed in the trimerization of butadiene: eleven tricyclic CH and one tetracyclic CH hydrocarbons, three of which had never been described before. The identification of these byproducts became possible by using a combination of chemical enrichment, high-resolution distillation, C-2D-INADEQUATE NMR, and comparison with ab initio calculated spectra, thus demonstrating the power of these combined techniques. The identification of these byproducts contributes to a better understanding of the mechanism of this centrally important reaction.