A [4+1] Cyclative Capture Approach to 3 H ‐Indole‐ N ‐oxides at Room Temperature by Rhodium(III)‐Catalyzed CH Activation

The rhodium(III)‐catalyzed [3+2] CH cyclization of aniline derivatives and internal alkynes represents a useful contribution to straightforward synthesis of indoles. However, there is no report on the more challenging synthesis of pharmaceutically important N ‐hydroxyindoles and 3 H ‐indole‐ N ‐oxides. Reported herein is the first rhodium(III)‐catalyzed [4+1] CH oxidative cyclization of nitrones with diazo compounds to access 3 H ‐indole‐ N ‐oxides. More significantly, this reaction proceeds at room temperature and has been extended to the synthesis of N ‐hydroxyindoles and N ‐hydroxyindolines.