Dioxypyrrolines. LV. Stereochemical Pathway of [2+2]Photocycloaddition Reaction of 4, 5-Diethoxycarbonyl-1H-pyrrole-2, 3-dione to Cycloalkadienes and Cycloalkenes

Abstract

The photocycloaddition reactions of 4, 5-diethoxycarbonyl-1H-pyrrole-2, 3-dione (6) to cycloalkadienes and cycloalkenes were examined. The addition of cyclopentadiene gave the hydroindole 8a (s+a product) as a major product and the cis-fused cyclobutane 7a (s+s product) as a minor one. In contrast, the addition of cyclohexadiene gave the cyclobutane 7b (s+s product) as a major product and the hydroidole 8b (s+a product) as a minor one. The photocycloaddition of cyclopentene, cyclohexene, and indene proceeded predominantly in an s+s manner to give the cis-syn-cis cyclobutanes, 16, 18, and 19, respectively. The stereochemical results were compared with those of the photocycloaddition reaction of 4-ethoxycarbonyl-5-phenyl-1H-pyrrole-2, 3-dione (1) to the corresponding cyclo-olefins, revealing that the steric relationship of the addends plays an important role in determining the stereochemical pathway of the reaction.