Synthesis of 2,3‐Disubstituted Indoles by Nickel(0)‐Catalyzed Migratory Cycloisomerization of o‐Alkynylanilides

We herein report a nickel‐catalyzed migratory cycloisomerization of o‐alkynylanilides, giving 2,3‐disubstituted indoles in good yields. The cyclization proceeded via acyl transfer on the nitrogen atom of the substrate to C3‐position in the product, and an N‐heterocyclic carbene (NHC) ligand such as ICy or SICy was found to be suitable in this reaction. It was thought that the reaction proceeds via an aza‐nickelcyclepentene intermediate formed from alkyne and the C=O bond of the amide moiety in o‐alkynylanilides. A nickel‐catalyzed migratory cycloisomerization of o‐alkynylanilides was investigated, and it was found to give 2,3‐disubstituted indoles. The cyclization was thought to proceed via an aza‐nickelcyclepentene intermediate formed from alkyne and the C=O bond amide moiety in the substrate, accompanied by acyl transfer on the nitrogen atom to the C3 position in the product.