Brønsted Acid‐Catalyzed Tandem Cyclizations of Tryptamine‐Ynamides Yielding 1H‐Pyrrolo[2,3‐d]carbazole Derivatives

Brønsted Acid‐Catalyzed Tandem Cyclizations of Tryptamine‐Ynamides Yielding... Ynamides, as versatile synthetic precursors, have attracted much attention from synthetic chemists and sparked the development of a number of methodologies for the construction of various structures. 1H‐Pyrrolo[2,3‐d]carbazole is a core scaffold of a series of monoterpene indole alkaloids found in Kopsia, Strychnos, and Aspidosperma, for example. In this study, 1H‐pyrrolo[2,3‐d]carbazole derivatives were synthesized by a Brønsted acid‐catalyzed tandem cyclization starting from tryptamine‐based ynamides. This strategy prevented Wagner–Meerwein rearrangement by instantaneous intramolecular nucleophilic trapping of the indoleninium to afford a tetracyclic indoline via an in situ‐formed enol species induced by the formation of a more stable conjugate diene moiety. The functional group tolerances were investigated by using a series of readily available substrates. A plausible mechanism has been proposed based on the evidence of the capture of the hemiaminal intermediate. Lastly, a Büchi ketone, which is the pivotal intermediate in the synthesis of the indole alkaloid vindorosine, was synthesized by utilizing our newly developed methodology. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Chemistry - A European Journal Wiley

Brønsted Acid‐Catalyzed Tandem Cyclizations of Tryptamine‐Ynamides Yielding 1H‐Pyrrolo[2,3‐d]carbazole Derivatives

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Publisher
Wiley
Copyright
© 2018 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
ISSN
0947-6539
eISSN
1521-3765
D.O.I.
10.1002/chem.201705189
Publisher site
See Article on Publisher Site

Abstract

Ynamides, as versatile synthetic precursors, have attracted much attention from synthetic chemists and sparked the development of a number of methodologies for the construction of various structures. 1H‐Pyrrolo[2,3‐d]carbazole is a core scaffold of a series of monoterpene indole alkaloids found in Kopsia, Strychnos, and Aspidosperma, for example. In this study, 1H‐pyrrolo[2,3‐d]carbazole derivatives were synthesized by a Brønsted acid‐catalyzed tandem cyclization starting from tryptamine‐based ynamides. This strategy prevented Wagner–Meerwein rearrangement by instantaneous intramolecular nucleophilic trapping of the indoleninium to afford a tetracyclic indoline via an in situ‐formed enol species induced by the formation of a more stable conjugate diene moiety. The functional group tolerances were investigated by using a series of readily available substrates. A plausible mechanism has been proposed based on the evidence of the capture of the hemiaminal intermediate. Lastly, a Büchi ketone, which is the pivotal intermediate in the synthesis of the indole alkaloid vindorosine, was synthesized by utilizing our newly developed methodology.

Journal

Chemistry - A European JournalWiley

Published: Jan 15, 2018

Keywords: ; ; ; ;

References

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