Merging Visible Light Photocatalysis and <scp>l</scp>-/<scp>d</scp>-Proline Catalysis: Direct Asymmetric Oxidative Dearomatization of 2-Arylindoles To Access C2-Quaternary Indolin-3-ones

Abstract

A mild and effective method for asymmetric synthesis of C2-quaternary indolin-3-ones directly from 2-arylindoles by combining visible light photocatalysis and organocatalysis is described. In this reaction, 2-substituted indoles undergo photocatalyzed oxidative dearomatization, followed by an organocatalyzed asymmetric Mannich reaction with ketones or aldehydes. Products with opposite configurations are easily obtained in satisfactory yields with excellent enantio- and diastereoselectivity by employing readily available l- and d-proline as chiral organocatalysts.