Alkylation of N-Protecting Group-free Indole with Vinyl Ketones Using Iron Salt Catalyst

Indole was reacted with vinyl ketones in the presence of 3 mol % of iron(II) tetrafluoroborate in acetonitrile or ionic liquids to give 3-alkylated product in an excellent yield. 2,3-Dialkylated indole was also obtained when the reaction was carried out using an excess amount of methyl vinyl ketone with the same catalyst; the results were significantly dependent on the reaction medium and both methanol and ionic liquid were found to be good solvents for double alkylation of indole.