Method
bis-indole synthesis from 2-iodoanilines and terminal diynes via sequential Sonogashira and cyclization reaction
- Description:
- Synthesis of analogs of types 5 and 6 from the paper
- Subjects:
- Keywords:
- indole, synthesis, Sonogashira, palladium, TBAF, CuI, bis-indole
cjdocken recommends this method
From: Convenient Indole Synthesis from 2-Iodoanilines and Terminal Alkynes by the Sequential Sonogashira Reaction and the Cyclization Reaction Promoted by Tetrabutylammonium Fluoride (TBAF)
by: Suzuki, Naoyuki; Yasaki, Sakura; Yasuhara, Akito; Sakamoto, Takao
CHEMICAL & PHARMACEUTICAL BULLETIN, 2003, 51(10), pp. 1170-1173
DOI: 10.1248/cpb.51.1170
Evaluation Results
- In your experience, how well did the method work?
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Using identical circumstances: -) Method not attempted under identical circumstances.
Using different circumstances: 4) My results were as good or better than the published example(s).
- Would you recommend this specific method/procedure or the general strategy/method outlined in the publication?
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Yes
- Details
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My syntheses of bis-indoles were usually (but not always) in the range of 30-60%, which was certainly acceptable for my purposes and comparable to the two examples in the paper. My substrates often contained an additional halogen, which was not reported in the paper. Both mesyl and acetyl-protected nitrogen substrates worked for me, as was reported. I often obtained significant amounts of recovered anilide starting material. I hypothesize that this may be due to decomposition of the diyne, of which I used only 0.5 eq to maximize the amount of dimeric product obtained. However, if some of the diyne decomposes in the reaction before it can react, larger quantities (perhaps added via slow addition) may be preferable.
In some cases I also isolated products where not all of the nitrogen protecting group had been hydrolyzed. Longer reaction times may remedy this. I did not invest time to optimize this bis-indole synthesis (which looks like it could be improved), but nonetheless I would certainly recommend the reported method. One potential disadvantage to the method is that the indole protecting groups (acetyl or mesyl) are removed in the course of the reaction, which might not be desired.