Thermal cycloaddition reaction of 4-benzoyl-5-ethoxycarbonyl-1H-pyrrole-2, 3-dione (dioxopyrroline) 1 with 1, 3-dienes caused two types of Diels-Alder (D-A) reaction in a competitive manner. One is the hetero D-A reaction in whch dioxopyrroline acts as an electron-deficient diene and the 1, 3-diene acts as an electron-rich dienophile. The other is the normal D-A reaction in which diosopyrroline acts as an electron-deficient dienophile. The 1, 3-dienes bearing electron-rich substituents undergo the D-A reaction via the normal pathway, while the 1, 3-dienes which do not bear an electron-donating group predominantly undergo the hetero D-A reaction. When the normal D-A pathway is sterically hindered, the hetero D-A pathway occurs exclusively.
4-苯甲酰基-5-乙氧基羰基-1H-
吡咯-2, 3-二酮(二氧代
吡咯啉)1与1, 3-二烯的热环加成反应以竞争方式引起两种类型的狄尔斯-阿尔德(D-A)反应。一种是杂D-A反应,其中二氧代
吡咯啉充当缺电子二烯,1, 3-二烯充当富电子亲二烯体。另一种是正常的 D-A 反应,其中二代
吡咯啉充当缺电子亲二烯体。带有富电子取代基的1, 3-二烯通过正常途径进行D-A反应,而不带有给电子基团的1, 3-二烯主要进行杂D-A反应。当正常的 D-A 途径受到空间阻碍时,异源 D-A 途径会排他地发生。