Iron salt-catalyzed cascade type one-pot double alkylation of indole with vinyl ketones

Indole was reacted with vinyl ketones in the presence of 5–8 mol % of iron (II) tetrafluoroborate or iron (III) perchlorate to give 2,3-dialkylated products; initial alkylation took place at 3-position on the indole ring and subsequent alkylation occurred at 2-position. It was found that the first alkylation proceeded very quickly, while the reaction rate of the second alkylation was very slow. Using this, cascade type synthesis of 2,3-dialkylated-indoles has been accomplished using iron (III)salt as catalyst.