Intramolecular Diels−Alder cycloaddition reactions of 1-(4-pentenoyl)-3-(tetrahydropyridinyl)indoles 7 followed by acid-catalyzed double-bond migration result in the stereoselective formation of novel pentaheterocyclic ring systems related to those of certain Strychnos alkaloids. The assignment of the stereochemistry of the cycloadducts was based on the analysis of 1D and 2D DQF−COSY and ROESY 1 H NMR spectra. 1-(4-Pentynoyl)-3-(tetrahydropyridinyl)indoles underwent an analogous cyclization to give the corresponding pentacyclic carbazoles in high yields.
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Gharagozloo et al. (1998) studied this question.
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