Scaffolds of tetrahydrocarbazoles are an important class of biologically active compounds found abundant in nature. In the present investigation, functionalized polycyclic tetrahydrocarbazoles were synthesized using Diels-Alder cycloaddition between fused 5-, 6- and 7-membered ring 2-vinylindoles and various dienophiles. The dienophiles used were N-phenylmaleimides, 1,4-naphthoquinone, and dimethyl acetylenedicarboxylate (DMAD). When 1,4-naphthoquinone was used as a dienophile, the 5-membered ring Diels-Alder adduct was obtained in the oxidized form, but this form was not observed in the case of 6- and 7-membered ring Diels-Alder adducts. The desired product yields ranged from 60–70% and the structure of final compounds were determined using 1D and 2D NMR analysis. 1H NMR studies confirmed excellent diastereoselectivity (>99% de).
Bibliographical noteFunding Information:
The authors thank the Wayland E. Noland Research Fellowship Fund at the University of Minnesota Foundation for generous financial support of this project. We are grateful to Dr. Kenneth J. Tritch and to all referees for constructive suggestions.