Thermal Diels‐Alder Reactions withN‐(2‐Alkenoyl)‐(S)‐proline Esters as Chiral DienophilesCyclopentadiene reacts withN‐acryloyl‐(S)‐proline benzyl and allyl ester in toluene at 0°C to give the bicycloheptene‐carboxylic acid amides with a stereoselection of (2S):(2R) = 81:19. In the reactions with theN,N′‐fumaroylbis(proline esters) the cycloadducts are formed in high yields and with isomer ratios of up to 97:3. The absolute configuration ofN,N′‐〈(1R,2R,3R,4S)‐bicyclo[2.2.1]hept‐5‐ene‐2,3‐diyldicarbonyl〉bis‐[(S)‐proline benzyl ester] (6 a) has been determined by an X‐ray analysis. In the reactions of the acrylamides with cyclopentadiene and of the fumaramides with cyclopentadiene, isoprene and 2,3‐dimethylbutadiene the use of water/ethanol mixtures as solvent, if indicated in the presence of detergents, doubles the yields. However, a positive influence of the aqueous medium