Ni(II)-Catalyzed Intramolecular C–H/C–H Oxidative Coupling: An Efficient Route to Functionalized Cycloindolones and Indenoindolones

• Published in: ACS catalysis 2021-10, Vol.11 (19), p.12384-12393
• Main Authors: Ankade, Shidheshwar B, Samal, Pragnya Paramita, Soni, Vineeta, Gonnade, Rajesh G, Krishnamurty, Sailaja, Punji, Benudhar
• Format: Article
• Language: English
• ISSN: 2155-5435; 2155-5435
• DOI: 10.1021/acscatal.1c03314

Nickel­(II)-catalyzed intramolecular C­(sp2)–H/C­(sp3)–H and C­(sp2)–H/C­(sp2)–H oxidative couplings in indoles are achieved via chelation assistance. These reactions provide access to biologically relevant five- and six-membered substituted cyclopentaindolones, carbazolones, and indenoindolones in high yields and good chemoselectivity employing an air-stable and defined nickel catalyst, (bpy)­Ni­(OAc)2. The oxidative cyclizations proceeded either through a six-membered or an unconventional seven-membered nickelacycle. An extensive mechanistic investigation by experiments and theoretical calculations revealed a facile indole’s C(2)–H nickelation and a rate-limiting reductive elimination process. This intramolecular oxidative cyclization operates via a probable Ni­(II)/Ni­(III) pathway involving single-electron oxidation of nickel without the participation of a carbon-based radical.