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

Abstract

Nickel(II)-catalyzed intramolecular C(sp 2 )−H/C-(sp 3 )−H and C(sp 2 )−H/C(sp 2 )−H oxidative couplings in indoles are achieved via chelation assistance. These reactions provide access to biologically relevant fiveand 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.

HFIP-mediated C-3-alkylation of indoles and synthesis of indolo[2,3-b]quinolines & related natural products

“…Alkylated indoles bearing active methylene groups, 9k , 10x and 10y , were subjected to visible light mediated carbonylation to indolyls 15a–c through a sustainable protocol. Further reaction of these indolyls with Pd-catalyzed cyclization led to indenoindolones ( 16a–c ) which exhibit enormous scope and diversity in medicinal chemistry and natural products 16–18 (Scheme 3).…”

Iron-catalyzed regioselective C–H alkylation of indoles: an additive-free approach in renewable solvent

“…11 Therefore, those promising processes in reducing waste and in achieving sustainable indole alkylation would be the judicious choices of coupling partners to avoid loss of atoms, involve additive-free processes, use minimum amounts of renewable solvent 12 or a solvent-free approach, and performing the reaction under mild conditions. With these objectives in mind, and as part of our research activity to address the limitations of existing indole alkylation reactions, 13 herein, we present the first iron-catalyzed additive-free, atom-economical and regioselective C(2)−H alkylation of indoles with alkenes in a reduced amount of renewable solvent or without any solvent under mild conditions (Scheme 1b). The reaction provides exclusive anti-Markovnikov selective linear alkylated indoles in excellent yields with remarkable tolerance of functionalities.…”

Rhodium(III)-Catalyzed C–H Cascade Annulation of Arylhydrazines with 2-Diazo-1,3-indandiones for the Synthesis of Tetracyclic Indeno[1,2-b]indoles

“…In recent decades, transition-metal-catalyzed C–H bond activation of compose heterocycles has emerged as a robust tool . Recently, this strategy has provided an important approach to tetracyclic indeno­[1,2- b ]­indole derivatives . In this regard, Kandekar’s and Punji’s group disclosed palladium or nickel-catalyzed intramolecular C–H activation of 3-indolylarylketone to synthesize tetracyclic indeno­[1,2- b ]­indoles, respectively (Scheme c).…”