Abstract
The substituent effect on the addition course of the Diels-Alder reaction of butadiene with 2-methyl-1, 4-benzoquinones which carry the cyano (V), dimethylcarbamoyl (VI), β-ethoxycarbonylethyl (VII), β-cyanoethyl (VIII), ethoxycarbonyl-trans-vinyl (IXa) group at the C5 position, respectively, was examined. The addition of V and VI occurred one-sidedly at the ethylene linkage carrying the electronwithdrawing cyano and dimethylcarbamoyl group. In the compound (VII and VIII), butadiene added at both ethylene linkages giving a mixture of adducts in the ratio of XXXIIa/XXXIIb=2/3 and XXXIIIa/XXXIIIb=1/1, respectively. The reaction of 2-methyl-5-(ethoxycarbonyl-trans-vinyl)-1, 4-benzoquinone (IXa) with butadiene furnished the adduct (XXXIVa), indicating that the addition occurred at the ethylene linkage bearing the unsaturated ester group.
