Calendula Oil – a New Feedstock for Chemical Syntheses
Ursula Biermann, University of Oldenburg, Department of Chemistry, P.O. Box 2503, D-26111 Oldenburg,
Tarik Eren, Bogazici University , Department of Chemistry, 80815 Bebek/Istanbul Jürgen O. Metzger, University of Oldenburg (same as above)
Oils and fats of vegetable and animal origin make up the greatest proportion of the current consumption of renewable raw materials in the chemical industry, since they offer to chemistry a large number of possibilities for applications which can be rarely met by petrochemistry. During the last few years modern synthetic methods have been applied extensively to fatty compounds for the selective functionalization of the C,C-double bond of unsaturated fatty compounds and gave a large number of novel fatty compounds from which interesting properties are expected.1 We are reporting here our results on chemical transformations of calendula oil.
Interesting products can be expected by addition reactions to the highly reactive hexatriene system of octadec-8,10-trans-12-cis-trienoic acid (calendic acid), the main fatty acid (ca.
60%) in the seed oil of calendula officinalis. Calendic acid methyl ester was obtained from the native oil by solid base catalyzed transesterification with methanol. The solvent-free Diels- Alder reaction of calendic acid methyl ester and maleic anhydride gave exclusively one highly functionalized cycloaddition product in 78% yield. The endo-8,12-cycloaddition product was formed with high regio- and stereoselectivity. The reaction can be applied to the native oil as well. At 200 – 300°C calendic acid methyl ester reacted in an electrocyclic reaction followed by aromatization to give an ortho-dialkyl substituted aromatic compound.
1 U. Biermann, W. Friedt, S. Lang, W. Lühs, G. Machmüller, J.O. Metzger, M. Rüsch gen. Klaas, H. Schäfer, M.P. Schneider, Angew. Chem. Int. Ed. 2000, 39, 2206-2224.
