Rhodium-Catalyzed CH Annulation of Nitrones with Alkynes: A Regiospecific Route to Unsymmetrical 2,3-Diaryl-Substituted Indoles

The direct CH annulation of anilines or related compounds with internal alkynes provides straightforward access to 2,3-disubstituted indole products. However, this transformation proceeds with poor regioselectivity in the synthesis of unsymmetrically 2,3-diaryl substituted indoles. Herein, we report the rhodium(III)-catalyzed CH annulation of nitrones with symmetrical diaryl alkynes as an alternative method to prepare 2,3-diaryl-substituted N-unprotected indoles with two different aryl groups. One of the aryl substituents is derived from NC-aryl ring of the nitrone and the other from the alkyne substrate, thus providing the indole products with exclusive regioselectivity.