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

Abstract

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.