Brønsted Acid‐Catalyzed Tandem Cyclizations of Tryptamine‐Ynamides Yielding 1H‐Pyrrolo[2, 3‐d]carbazole Derivatives. Issue 16 (10th January 2018)

• Record Type: Journal Article
• Authors: Wang, Yanshi; Lin, Jingsheng; Wang, Xiaoyu; Wang, Guanghui; Zhang, Xinhang; Yao, Bo; Zhao, Yuandong; Yu, Pengfei; Lin, Bin; Liu, Yongxiang; Cheng, Maosheng
• Is Part Of: Chemistry. Volume 24:Issue 16(2018)
• Page Start: 4026
• Page End: 4032
• Publication Date: 2018-01-10
• Subjects: cyclization -- fused-ring systems -- heterocycles -- ketones -- synthetic methods; Chemistry -- Periodicals; 540
• DOI: 10.1002/chem.201705189
• Languages: English
• ISSNs: 0947-6539

Abstract

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. 1 H ‐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, 1 H ‐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. Abstract : Tandem cycling : A two‐step transformation leading to the synthesis of 1 H ‐pyrrolo[2, 3‐ d ]carbazole derivatives starting from tryptamine‐based ynamides has been developed and applied to the formal synthesis of vindorosine (see scheme). A plausible mechanism for this tandem cyclization was probed by capturing the reaction intermediate.