CYCLOADDITIONS OF PYRANOINDOL-3-ONES WITH 1,2-BIS-ACCEPTOR SUBSTITUTED ETHENES: FIRST EVIDENCE FOR A NON-CONCERTED DIELS-ALDER STEP

Article abstract of DOI:10.3987/COM-90-5517

The Diels-Alder reactions of pyrano<3,4-b>indol-3-ones (1) with 1,2-bis-acceptor substituted ethenes yield stable 1,2-dihydrocarbazoles and fully aromatized carbazoles.The results of stereochemical determinations in the 1,2-dihydrocarbazoles and, in one case, the occurrence of a bimolecular, diene-catalyzed dienophile isomerization provide the first evidence that a non-concerted <4 + 2>cycloaddition is mainly in operation.The pyrido<3,4-b>indol-3-one (11) was attacked by dienophiles only at the lactam nitrogen atom and cycloaddition did not take place.