Transition-metal trifluoromethane-sulphonates -recyclable catalysts for the synthesis of branched fatty derivatives by Diels-Alder reactions at unsaturated fatty esters

Abstract

Diels-Alder reactions of conjugated linoleic acid ethyl ester (1) with different quinones and with a variety of α/β-unsaturated aldehydes and ketones are described in this paper. Using Sc(OTf)3 or Cu(OTf)2 as catalysts the reactions can be carried out at 25-40 °C with good yields. For the first time in oleochemistry it is possible to prepare Diels-Alder cycloadditions with catalyst concentrations of 10 mol-% instead of stoichiometric amounts of Lewis acids. Furthermore, the reaction time was partly shortened drastically. The catalyst Sc(OTf)3 can be removed by a simple extraction of the organic layer with water. After evaporation of the aqueous phase to dryness the catalyst can be reused without loss of yield.