Unified Strategy for Nickel-Catalyzed C‑2 Alkylation of Indoles through Chelation Assistance

A nickel-catalyzed
direct C-2 alkylation of indoles through monodentate-chelation
assistance has been described. This reaction proceeds via an unusual
strategy by the use of a well-designed and defined (quinolinyl)­amido–nickel
catalyst, [{κN,κN,κN-Et2NCH2C­(O)­(μ-N)­C9H6N}­Ni­(OAc)], providing a solution to the limitations associated with
bidentate-chelate auxiliaries. The method allows coupling of indoles
with various unactivated primary and secondary alkyl halides with
ample substrate scope. This uniquely strategized alkylation proceeded
through crucial C–H activation and via an alkyl radical intermediate.
The reaction by this approach represents a rare example of Ni-catalyzed
monodentate-chelate-assisted C–H functionalization.