The Diels-Alder reaction has been examd. in room temp. ionic liqs. with high molar concns. of Lewis acids under various conditions. A molar ratio of 10% catalyst gave a large increase in the selectivity and the yield of the reaction. The effect of catalysts on reaction rates was also examd. under 100 MPa of pressure which leads to modest improvements in reaction rates. Ultrasound and microwave dielec. heating were also shown to improve the rate and, to a minor extent, selectivity of the examd. reactions.