Regio- and stereoselective Diels-Alder additions of maleic anhydride to conjugated triene fatty acid methyl esters

The thermal, solvent-free addition of maleic anhydride to methyl calendulate (methyl 8, 10-trans, 12-cis-octadecatrienoate) (1a) occurs with very high regio- and stereo selectivity at C-8 and C-11 of the fatty compound giving the endo-Diels-Alder adduct 4 with retention of the cis-configured double bond. Analogously, the Diels-Alder addition of maleic anhydride to methyl alpha-eleostearate (methyl 9-cis,11,13-trans-octadecatrienoate) (2a) takes place regio- and stereoselectively at C-11 and C-14 yielding the endo-product 5 which was hydrolyzed to give the respective tricarboxylic acid 6. X-ray diffraction analyses of compounds 4 and 6 clearly show the regio- and stereoselectivity of the Diels-Alder addition reactions. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).