Norbornadiene-fused heterocycles: Syntheses and cycloaddition reactions of 2-aryl-4,7-dihydro-4,7-methano-2H-isoindoles and 4,7-dihydro-4,7-methanoisobenzofuran

Article abstract of DOI:10.1246/bcsj.68.3269

2-Phenyl- and 2-(p-tolyl)-4,7-dihydro-4,7-methano-2H-isoindole were synthesized by treatment of 3-(diethoxymethyl)bicyclo[2.2.1]hepta-2,5-diene-2-carbaldehyde with aniline or p-toluidine, followed by reduction with sodium borohydride and acid-catalyzed cyclization. It was concluded that the previous claim of the synthesis of methanoisoindole derivatives was incorrect. 4,7-Dihydro-4,7-methanoisobenzofuran was prepared by the reduction of the norbornadiene-monocarbaldehyde with sodium borohydride and subsequent treatment with Amberlyst-15. The p-tolylmethanoisoindole reacted with dimethyl acetylenedicarboxylate to give a novel 1:3 adduct. On the other hand, in the reaction of the methanoisobenzofuran with N-phenylmaleimide, spontaneous oxidation of the Diels-Alder cycloadduct took place to give exclusively its epoxide.