Journal
CHEMCATCHEM
Volume 6, Issue 8, Pages 2333-2338Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cctc.201402309
Keywords
alkylation; alkenes; electrophilic addition; nitrogen heterocycles; phosphorus
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Funding
- Japan Society for the Promotion of Science (JSPS)
- Ministry of Education, Culture, Science, Sports, and Technology of Japan
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Catalytic N-alkylation of indoles is challenging because the N1 nitrogen atoms are inert toward electrophilic reagents. Herein, an organic-solvent-soluble alkylammonium salt of a simple monomeric phosphate ion, [PO4](3-), with a high charge density acts as an efficient homogeneous catalyst for selective N-alkylation of indoles with alpha,beta-unsaturated compounds. For the reaction of indole with ethyl acrylate, the turnover number reached up to 36 and the turnover frequency was 216 h(-1); these values are the highest among those reported for base-mediated systems so far. In the presence of [PO4](3-) ions, various combinations of nitrogen nucleophiles (ten examples) and alpha,beta-unsaturated compounds (four examples) were efficiently converted to the desired N-alkylated products in high yields. NMR and IR spectroscopies showed formation of the indolyl anion through the activation of indole by the [PO4](3-) ion, which plays an important role in the present N-alkylation.
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