Synthesis of fatty acid-based 3,6-disubstituted-1,2,3,6-tetrahydro-phthalic acid anhydride derivatives

Fatty acid based 3,6-disubstituted-1,2,3,6-tetrahydro-phthalic acid anhydride derivatives were synthesized by Rhodium catalysed addition of maleic anhydride to linoleic and oleic acid. The maleinisation of linoleic acid leads to cyclohexenoic anhydrides having an allylic double bond. The cis-configuration of this double bond was confirmed by synthesis of the corresponding anhydrides via Diels-Alder reaction of calendic acid, alpha-eleostearic acid and beta-eleostearic acid with maleic anhydride, which was reported to be highly regio- and stereoselective. These compounds were co-injected with the products of the Rh-catalysed maleinated linoleic acid into HPLC column so that the peaks of the resulting chromatogram could be allocated to the corresponding cyclohexenoic anhydrides. Besides the activity of the used catalysts RhCl3(H2O)3 and Rh(OAc)2, their selectivity towards the cyclohexenoic anhydrides was investigated. Furthermore the influence of reaction temperature, equivalents of maleic anhydride and reaction time was analysed to determine the optimum reaction conditions for the highest overall yields of the resulting 3,6-disubstituted-1,2,3,6-tetrahydro-phthalic acid anhydride derivatives.