@article {45528, title = {Nickel-catalyzed straightforward and regioselective C-H alkenylation of indoles with alkenyl bromides: scope and mechanistic aspect}, journal = {ACS Catalysis}, volume = {9}, year = {2019}, month = {JAN}, pages = {431-441}, type = {Article}, abstract = {

Nickel-catalyzed regioselective C-H bond alkenylation of indoles and related heteroarenes with alkenyl bromides is accomplished under relatively mild conditions. This method allows the straightforward synthesis of C-2 alkenylated indoles employing an air-stable and well-defined nickel catalyst, (bpy)NiBr2, providing a solution to the limitations associated with hydroindolation and oxidative alkenylation. The reaction conceded the coupling of indole derivatives with various alkenyl bromides, such as aromatic and heteroaromatics, alpha- and beta-substituted as well as exo- and endo-cyclic alkenyl compounds. An extensive mechanistic investigation, including controlled study, reactivity experiments, kinetics and labeling studies, and EPR and XPS analyses, highlights that the alkenylation proceeds through a single-electron transfer process comprising an odd-electron oxidative addition of alkenyl bromide. Furthermore, the alkenylation operates via a probable Ni(I)/Ni(III) pathway involving the rate-limiting C-H nickelation of indole.

}, keywords = {alkenylation, C-H activation, indoles, Mechanism, Nickel, single-electron transfer}, issn = {2155-5435}, doi = {10.1021/acscatal.8b04267}, author = {Jagtap, Rahul A. and Vinod, C. P. and Punji, Benudhar} } @article {47638, title = {Ni(II)-catalyzed intramolecular C-H/C-H oxidative coupling: an efficient route to functionalized cycloindolones and indenoindolones}, journal = {ACS Catalysis}, volume = {11}, year = {2021}, month = {OCT }, pages = {12384-12393}, type = {Article}, 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 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{\textquoteright}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.}, keywords = {C-H activation, cycloindolones, indenoindolones, indoles, Mechanism, Nickel, oxidative coupling}, issn = {2155-5435}, doi = {10.1021/acscatal.1c03314}, author = {Ankade, Shidheshwar B. and Samal, Pragnya Paramita and Soni, Vineeta and Gonnade, Rajesh G. and Krishnamurty, Sailaja and Punji, Benudhar} } @article {48083, title = {Efficient route to 3,3 {\textquoteleft}-biindolinylidene-diones by iron-catalyzed dimerization of isatins}, journal = {Chemistry-an Asian Journal}, volume = {17}, year = {2022}, month = {AUG}, pages = {e202200414}, type = {Article}, abstract = {

Iron-catalyzed dimerization of various isatin derivatives is described for the efficient synthesis of 3,3 {\textquoteleft}-biindolinylidene-diones (isoindigos). The reaction provides easy access to self-coupled and cross-coupled 3,3 {\textquoteleft}-indolinylidene-diones that have high relevance to biology and materials. This Fe(0)- or Fe(II)-catalyzed dimerization reaction tolerates a wide range of functionalities, such as fluoro, chloro, bromo, alkenyl, nitrile, ether, ester, pyrrolyl, indolyl and carbazolyl groups, including cyclic and acyclic alkyls as well as an alkyl-bearing fatty-alcohol moiety. Especially, the coupling between two distinct isatins provided excellent selectivity for the cross-dimerization with trace of self-couplings. The single-crystal X-ray diffraction study established the molecular structure of eight dimerized products. A preliminary mechanistic study of the Fe-catalyzed dimerization supported the radical pathway for the reaction.

}, keywords = {Cross-coupling, dimerization, iron, Isatin, Isoindigo, Mechanism}, issn = {1861-4728}, doi = {10.1002/asia.202200414}, author = {Jagtap, Rahul A. and Pradhan, Chandini and Gonnade, Rajesh G. and Punji, Benudhar} } @article {49125, title = {Advances in the iron-catalyzed direct functionalizations of heterocycles}, journal = {Synlett}, volume = {34}, year = {2023}, month = {APR}, pages = {683-697}, type = {Article}, abstract = {

Direct functionalization of heterocycles is an advanced strategy for diversifying privileged and biorelevant heterocycle-containing molecules. Particularly, use of the most abundant transition metal, iron, as a catalyst makes this process highly cost-effective and sustainable. Recently, some progress has been realized towards the direct functionalization of heterocycles under iron catalysis. Herein, we present the developments in the C-H bond functionalizations and related reactions of various heterocycles by abundant iron salts. This Synpacts is categorized into different sections based on heterocycles being functionalized, and each section is discussed based on the type of reaction catalyzed by iron. 1 Introduction 2 Functionalization of Indoles 2.1 Alkylation 2.2 Alkenylation 2.3 Other Reactions 3 Oxindoles and isatins 3.1 C-C Bond Formation 3.2 C-Heteroatom Bond Formation 4 Pyridines and Furans 5 Functionalization of Azoles 6 Summary and Outlook

}, keywords = {Alkylation, azoles, C-H functionalization, heterocycles, indoles, iron, Mechanism}, issn = {0936-5214}, doi = {10.1055/a-1890-8503}, author = {Pradhan, Chandini and Punji, Benudhar} } @article {49551, title = {Hybrid pincer (PNN)Ni(II) complex catalyzed selective C-H alkylation of pyridones using unactivated alkyl chlorides}, journal = {ACS Catalysis}, volume = {15}, year = {2025}, month = {FEB}, pages = {2987-2999}, type = {Article}, abstract = {

The use of readily accessible unactivated alkyl chlorides in the alkylation reaction to install valuable alkyl and methyl motifs into privileged heterocycles is an underdeveloped area. Herein, we report the regioselective C-H alkylation of diverse pyridones employing challenging unactivated alkyl chlorides as coupling partners, enabled by a strategically developed quinolinyl-based pincer (Ph2PNNQ)Ni(II) complex. The air-stable nickel catalyst is highly effective for the selective alkylation of functionalized 2-pyridones with both primary and secondary alkyl chlorides as well as for the unexpected C6 methylation, furnishing a wide range of 6-alkyl-2-pyridone scaffolds (78 examples). Remarkably, the alkyls bearing biologically and pharmacologically significant motifs, such as pterostilbene, nonyl phenol, sesamol, estrone, vitamin E, stigmasterol, cholesterol, and diosgenin, were compatible under this catalytic approach. The insights into the mechanism suggest that the alkylation reaction follows a Ni(II)/Ni(III)/Ni(IV) pathway involving the crucial two-step, one-electron oxidative addition of alkyl chloride. Several control studies, kinetics, and EPR analyses were performed to understand the detailed reaction pathway, further supported by density functional theory calculations.

}, keywords = {alkyl chlorides, C-H/C-Cl activation, hybrid pincer ligand, Mechanism, Nickel, pyridones}, issn = {2155-5435}, doi = {10.1021/acscatal.4c07173}, author = {Verma, Suryadev K. and Samal, Pragnya Paramita and Pradhan, Chandini and Pandey, Dilip K. and Krishnamurty, Sailaja and Punji, Benudhar} }