@article {44627, title = {Copper- and phosphine-free nickel(II)-catalyzed method for C-H bond alkynylation of benzothiazoles and related azoles}, journal = {Asian Journal of Organic Chemistry}, volume = {7}, year = {2018}, month = {JUL}, pages = {1390-1395}, abstract = {

A phosphine-free nickel(II)-catalyzed method for the C(2)-H bond alkynylation of (benzo)thiazoles, (benz)imidazoles, and oxazoles is described. Well-defined and air-stable (Phen)NiCl2 catalyst efficiently catalyzes the coupling of diverse azoles with alkynyl bromides without the use of a copper co-catalyst, and the method tolerates synthetically important functional groups. Preliminary mechanistic studies on this Ni-II-catalyzed alkynylation emphasize the homogeneous nature of the catalyst, and rule out a radical manifold for the reaction. The synthetic utility of this Ni-catalyzed method is demonstrated by further functionalizing the alkynylated benzothiazoles to 3-methyl-2-(alkynyl)benzo[d]thiazolium salts that are known DNA cleaving agents.

}, keywords = {alkynylation, azoles, C-H activation, heterocycles, Nickel}, issn = {2193-5807}, doi = {10.1002/ajoc.201800243}, author = {Patel, Ulhas N. and Punji, Benudhar} } @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 {46673, title = {Expeditious and solvent-free nickel-catalyzed c-h arylation of arenes and indoles (vol 10, pg 2242, 2017)}, journal = {ChemSusChem}, volume = {13}, year = {2020}, month = {NOV }, pages = {5771}, type = {Correction}, keywords = {Arylation, C-H activation, heterocycles, Homogeneous catalysis, Nickel}, issn = {1864-5631}, doi = {10.1002/cssc.202002313, Early Access Date = OCT 2020}, author = {Jagtap, Rahul A. and Soni, Vineeta and Punji, Benudhar} } @article {47412, title = {Nickel-catalyzed C-H bond functionalization of azoles and indoles}, journal = {Chemical Record}, volume = {21}, year = {2021}, month = {DEC}, pages = {3573-3588}, type = {Article}, abstract = {

Direct C-H functionalization of privileged and biologically relevant azoles and indoles represents an important chemical transformation in molecular science. Despite significant progress in the palladium-catalyzed regioselective C-H functionalization of azoles and indoles, the use of abundant and less expensive nickel catalyst is underdeveloped. In the recent past, the nickel-catalyzed regioselective C-H alkylation, arylation, alkenylation and alkynylation of azoles and indoles have been substantially explored, which can be applied to the complex organic molecule synthesis. In this Account, we summarize the developments in nickel-catalyzed regioselective functionalization of azoles and indoles with a considerable focus on the reaction mechanism.

}, keywords = {azoles, C-C Bond formation, C-H functionalization, indoles, Nickel}, issn = {1527-8999}, doi = {10.1002/tcr.202100113, Early Access Date = JUN 2021}, author = {Jagtap, Rahul A. 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 {49298, title = {Nickel-catalyzed branch-selective C-H alkylation of indoles and azoles with alkenes: an additive- and solvent-free approach}, journal = {European Journal of Organic Chemistry}, volume = {27}, year = {2024}, month = {JUL }, type = {Article}, abstract = {

The development of sustainable protocols for the synthesis of alkylated heteroarenes is crucial owing to their widespread existence in medicinally relevant and bioactive natural products. Herein, we describe an efficient, additive- and solvent-free approach for the regioselective C-H alkylation of indoles and azoles with alkenes using a nickel catalyst, which proceeds through a chelation-assistance strategy. The reaction exclusively provided branched alkylated products with the compatibility of alkyl, alkoxy, fluoro, trifluoromethyl, alkene, cyano, ester, and carbonyl groups. This protocol is applicable to other heteroarenes, such as imidazoles and benzimidazoles, providing the desired alkylated products with exclusive Markovnikov selectivity. The synthetic utility and scale-up of the reaction are demonstrated, and the protocol is in concord with the principles of green chemistry. Alkylation proceeds through facile and reversible C-H nickelation and alkene insertion processes, presumably involving rate-limiting reductive elimination. A straightforward nickel-catalyzed protocol for the C-H alkylation of indoles and azoles is disclosed that proceeds under additive- and solvent-free conditions. The reaction utilizes readily available alkenes as alkylating partners and delivers Markovnikov products with tolerance of sensitive functionalities. image

}, keywords = {Alkylation, branch selectivity, indoles, Nickel, solvent-free synthesis}, issn = {1434-193X}, doi = {10.1002/ejoc.202400376}, author = {Ankade, Shidheshwar B. and Banerjee, Shuvajit and Punji, Benudhar} } @article {49023, title = {Nickel-catalyzed chemodivergent coupling of alcohols: efficient routes to access α,α-disubstituted ketones and α-substituted chalcones}, journal = {Chemistry- a european journal}, volume = {30}, year = {2024}, month = {MAR}, type = {Article}, abstract = {

Chemodivergent (de)hydrogenative coupling of primary and secondary alcohols is achieved utilizing an inexpensive nickel catalyst, (6-OH-bpy)NiCl2. This protocol demonstrates the synthesis of branched carbonyl compounds, alpha,alpha-disubstituted ketones, and alpha-substituted chalcones via borrowing hydrogen strategy and acceptorless dehydrogenative coupling, respectively. A wide range of aryl-based secondary alcohols are coupled with various primary alcohols in this tandem dehydrogenation/hydrogenation reaction. The nickel catalyst, along with KOtBu or K2CO3, governed the selectivity for the formation of branched saturated ketones or chalcones. A preliminary mechanistic investigation confirms the reversible dehydrogenation of alcohols to carbonyls via metal-ligand cooperation (MLC) and the involvement of radical intermediates during the reaction. The chemodivergent nickel-catalyzed approach provides alpha,alpha-disubstituted ketones from aryl-substituted secondary alcohols and benzyl alcohols via the borrowing hydrogen (BH) strategy in the presence of KOtBu, whereas exclusively alpha-substituted chalcones were accomplished in the presence of mild base K2CO3 through an acceptorless dehydrogenative coupling (ADC) strategy. image

}, keywords = {Alcohols, dehydrogenative coupling, Metal-ligand cooperation, Nickel, substituted carbonyl compounds}, issn = {0947-6539}, doi = {10.1002/chem.202304082}, author = {Bansal, Sadhna 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} }