Indium-Catalyzed Reductive Alkylation of Indoles

indoles - reductive alkylation - indium

Significance

Herein, an indium-catalyzed reductive alkylation of indoles is reported. The protocol tolerates a broad scope of functional groups and allows a flexible combination of indoles and alkynes affording alkylindoles in good yields. The preferred nucleophiles are hydrosilanes; however, carbon nucleophiles, such as trimethylsilyl cyanide or methoxythiophene, can also be used.

Comment

Depending on the structure of the substrate, the authors suggest two different ­reaction mechanisms. For 2-substituted indoles, the first step is a single addition to the indium-­activated alkyne followed by hydride reduction and regeneration of the catalyst. Unsubstituted ­indoles undergo a double addition to the alkyne resulting in diindolylalkanes before indium elimination and hydride transfer occurs.