Dioxopyrrolines. LXI. Cycloaddition reaction of 4-benzoyl-5-ethoxycarbonyl-1-phenyl-1H-pyrrole-2,3-dione with 1,3-dienes: Competitive occurrence of normal and hetero Diels-Alder reaction and Claisen rearrangement of the hetero Diels-Alder product

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 which 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 dioxopyrroline 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.