Fuse S, Kanda S, Masui H. One-Flow Synthesis of Substituted Indoles via Sequential 1,2-Addition/Nucleophilic Substitution of Indolyl-3-Carbaldehydes.
Chem Asian J 2024;
19:e202300909. [PMID:
37962410 DOI:
10.1002/asia.202300909]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2023] [Revised: 11/13/2023] [Accepted: 11/14/2023] [Indexed: 11/15/2023]
Abstract
Substituted indoles are important as drugs. A number of valuable indoles have been synthesized via nucleophilic substitution at the 3'-position of indoles. However, the preparation of an indolylmethyl electrophile containing a tertiary carbon at the 3'-position and its subsequent nucleophilic substitution are challenging owing to the instability of the electrophile. Herein, we demonstrated the rapid one-flow synthesis of indoles via sequential 1,2-addition/nucleophilic substitution of indolyl-3-carbaldehydes. The use of a microflow technology helped in suppressing the undesired reactions caused by the unstable intermediates, resulting in significantly higher yields and reproducibility compared to those under batch conditions. A crown ether was effective when 1-alkylindole-3-carboxaldehyde was used as a substrate. However, the crown ether exerted a detrimental effect when 1H-indole-3-carboxaldehyde was used. A total of 15 structurally diverse indole derivatives were obtained in generally acceptable to good yields.
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