Selective Iron Catalyzed Synthesis of N‐Alkylated Indolines and Indoles

Whereas iron catalysts usually promote catalyzed C3‐alkylation of indole derivatives via a borrowing‐hydrogen methodology using alcohols as the electrophilic partners, this contribution shows how to switch the selectivity towards N‐alkylation. Thus, starting from indoline derivatives, N‐alkylation was efficiently performed using a tricarbonyl(cyclopentadienone) iron complex as the catalyst in trifluoroethanol in the presence of alcohols leading to the corresponding N‐alkylated indoline derivatives in 31–99 % yields (28 examples). The one‐pot, two‐step strategy for the selective N‐alkylation of indolines is completed by an oxidation to give the corresponding N‐alkylated indoles in 31–90 % yields (15 examples). This unprecedented oxidation methodology involves an iron salt catalyst associated with (2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl (TEMPO) and a stoichiometric amount of t‐BuOOH at room temperature.