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Organocatalytic Asymmetric Dearomative Oxyalkylation of Indoles Enables Access to C2-Quaternary Indolin-3-ones.

A facile and efficient asymmetric dearomative oxyalkylation of indoles with TEMPO oxoammonium salt and a variety of aldehydes and ketones has been described. This metal-free approach provides a straightforward access to C2 quaternary oxindoles in high yields with excellent diastereo- and enantioselectivities under very mild conditions. The reaction goes smoothly even with only 0.1% equivalent catalyst. Moreover, 2-alkylindoles have proven to be suitable substrates for the first time.