Total Synthesis of (±)‐Quebrachamine via [3+2] Cycloaddition and Efficient Chloroacetamide Photocyclization

Abstract

The total synthesis of (±)‐quebrachamine has been completed in 13 linear steps and 17.8 % overall yield. The indole core was constructed via a formal [3+2] dipolar cycloaddition between a functionalized nitrile and donor‐acceptor cyclopropane, and the synthetically challenging nine‐membered ring was secured by an efficient chloroacetamide photocyclization.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Heterocycles from cyclopropanes: applications in natural product synthesis

“…48 The synthetic sequence proceeds through indole 93 (previously used for the synthesis of goniomitine, Scheme 21), illustrating the usefulness of this intermediate for the divergent preparation of members of this alkaloid class. Early attempts to convert 93 into the natural product relied on a variety of Friedel-Crafts and N-alkylation strategies, but these methods proved unsuitable for the construction of the nine-membered ring.…”

Synthesis and Reactivity of Donor-Acceptor Substituted Aminocyclopropanes and Aminocyclobutanes

“…Their unique reactivity and their combination with various 1,3 formal dipoles gave access to diverse structures such as pyrrolines [116][117][118][119][120][121][122] or pyrroles [123][124][125][126][127]. Their unique reactivity and their combination with various 1,3 formal dipoles gave access to diverse structures such as pyrrolines [116][117][118][119][120][121][122] or pyrroles [123][124][125][126][127].…”

Die Witkop‐Cyclisierung: eine photoinduzierte C‐H‐Aktivierung des Indolsystems

“…[15] Eines der wenigen Beispiele mit hoher Ausbeute bei der Witkop-Reaktion ist die Synthese von (AE)-Quebrachamin (41) durch Pagenkopf und Bajtos. [16] Auch hier wurden zuvor zwei andere Wege verfolgt, um die gewünschte C-C-Knüp-fung zu erreichen, bevor die Witkop-Cyclisierung zum Erfolg führte. Der erste Ansatz beinhaltet eine Friedel-Crafts-Acylierung an der Indol-3-Position (Scheme 7 A), wohingegen der zweite eine N-Alkylierung des 3-substituierten Indol 37 zum Ziel hatte (Schema 7 B).…”