[4+2]Cycloadditions of Pyrano[3,4-b]indol-3-ones with 1,2-Bis-acceptor Substituted Ethenes: First Evidence for a Non-concerted Diels-Alder Step

Abstract

AbstTact -The Diels-Alder reactions of pyranoC3.4-plindol-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 14 + Zlcycloaddition is mainly in operation.me pyridoC3.4-plindol-3-one(11) was attacked by dienophiles only at the lactam nitrogen atom and cycloaddition did not take place.