Catalytic N-alkylation of indoles is challenging because the N1 nitrogen atoms are inert toward electrophilic reagents. Herein, an org.-solvent-sol. alkylammonium salt of a simple monomeric phosphate ion, [PO4]3-, with a high charge d. acts as an efficient homogeneous catalyst for selective N-alkylation of indoles with ﾎｱ,ﾎｲ-unsatd. compds. For the reaction of indole with Et acrylate, the turnover no. 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 ﾎｱ,ﾎｲ-unsatd. compds. (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. [on SciFinder(R)]
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