A Copper‐ and Phosphine‐Free Nickel(II)‐Catalyzed Method for C−H Bond Alkynylation of Benzothiazoles and Related Azoles

Patel, Ulhas N.; Punji, Benudhar

doi:10.1002/ajoc.201800243

Cited by 12 publications

(9 citation statements)

References 92 publications

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“…To address these limitations, we have developed an air-stable and phosphinefree catalyst system, (phen)NiCl 2 , for the alkynylation of various azoles, thiazoles and imidazoles (Scheme 11b). [40] This protocol demonstrated a wide range of substrates scope without employing a copper co-catalyst. Notably, many 3methyl-2-(alkynyl)benzo[d]thiazolium salts were synthesized employing this method that are known DNA cleaving agents.…”

Section: Alkynylation Of Azolesmentioning

confidence: 98%

“…Notably, the use of highly sensitive Ni(cod) 2 and further use of Cu‐cocatalyst are the drawbacks of this protocol. To address these limitations, we have developed an air‐stable and phosphine‐free catalyst system, (phen)NiCl 2 , for the alkynylation of various azoles, thiazoles and imidazoles (Scheme 11b) [40] . This protocol demonstrated a wide range of substrates scope without employing a copper co‐catalyst.…”

Section: C−h Bond Functionalization Of Azolesmentioning

confidence: 99%

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Nickel‐Catalyzed C−H Bond Functionalization of Azoles and Indoles

Jagtap

Punji

2021

The Chemical Record

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Direct CÀ 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 CÀ 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 CÀ 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.

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Section: Alkynylation Of Azolesmentioning

confidence: 98%

Section: C−h Bond Functionalization Of Azolesmentioning

confidence: 99%

Nickel‐Catalyzed C−H Bond Functionalization of Azoles and Indoles

Jagtap

Punji

2021

The Chemical Record

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“…In 2018, Punji demonstrated the direct alkynylation of azoles with alkynylbromides by using (phen)NiCl 2 4 complex (Scheme 8C). 98 Diverse azoles, such as benzothiazole, oxazole, and benzimidazole showed efficient coupling with triisopropylsilyl-or aryl-substituted alkynyl bromides and the reaction tolerated a wide variety of functional groups. The reaction was not affected by the presence of radical scavenger 2,2,6,6-tetramethylpiperidine1-oxyl TEMPO, which rules out the intermediacy of a radical species.…”

Section: Reviewmentioning

confidence: 99%

Nickel-Catalyzed C−H Functionalization Using A Non-directed Strategy

Khake

Chatani

2020

Chem

119

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The activation of ubiquitous C-H bonds has great significance in the field of organic synthesis given that it represents an ideal method for directly producing valuable chemicals from structurally simple compounds. First-row transition metals have recently been recognized as a potential alternative to noble transition metals because of their low cost, unique reactivity profiles, and easy availability. Among these metals, nickel (Ni) catalysts have drawn considerable attention from the scientific community. This review focuses on Ni-catalyzed C-H functionalization reactions of (hetero)arenes, including alkylation, arylation, alkenylation, alkynylation, borylation, and trifluoromethylation by using non-directing group strategies. In addition, mechanistic aspects of Ni-catalyzed C-H functionalization reactions are discussed because this allows possible new insights into catalyst improvement.

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“…Various transition-metal catalysts have been known for the C–H bond alkynylation of different arenes and heteroarenes, including indoles . Specifically, the earth-abundant and inexpensive 3d metals, such as Fe, Co, Ni, Cu have been successfully employed for the alkynylation of activated azoles and benzamides, and been found to be more beneficial. Shi and Ackermann have individually shown the C-2 alkynylation of indoles by cobalt catalysis employing different alkynyl coupling partners.…”

Section: Introductionmentioning

confidence: 99%

Mechanism of Nickel(II)-Catalyzed C(2)–H Alkynylation of Indoles with Alkynyl Bromide

Khake

Jain²,

Patel

et al. 2018

Organometallics

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The nickel system (THF)2NiBr2/phen has recently been shown as an efficient catalyst for the C–H bond alkynylation of diverse heteroarenes with (triisopropylsilyl)alkynyl bromide via monodentate chelation assistance. Herein, we report an extensive mechanistic investigation for the direct alkynylation of indoles involving the well-defined nickel catalyst, which features a coordinative insertion pathway of alkynyl bromide with the Ni(II) catalyst. Catalytic relevant nickel complexes, (phen)NiCl2 (5), (phen)2NiCl2 (6) and [(phen)3Ni]·NiCl4 (7) were isolated, and the complexes 6 and 7 were structurally characterized. Well-defined complexes were as competent as the in situ generated catalyst system (THF)2NiBr2/phen for the alkynylation of indoles. Various controlled studies and reactivity experiments were performed to understand the probable pathway for the alkynylation reaction. Kinetics analysis highlights that the complex (phen)NiX2 acts as a precatalyst, and the involvement of substrate indole and LiO t Bu are essential for the generation of the active catalyst. Deuterium labeling and kinetic studies suggest that the process involving C–H cleavage and carbo-nickelation of indole is a crucial rate influencing step. Reactivity study of various alkynyl compounds with nickel-species highlights a migratory insertion route for the reaction. DFT calculations firmly support the experimental findings and suggest the coordinative insertion pathway of alkynyl bromide rather than oxidative addition toward the nickel(II) center.

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A Copper‐ and Phosphine‐Free Nickel(II)‐Catalyzed Method for C−H Bond Alkynylation of Benzothiazoles and Related Azoles

Cited by 12 publications

References 92 publications

Nickel‐Catalyzed C−H Bond Functionalization of Azoles and Indoles

Nickel‐Catalyzed C−H Bond Functionalization of Azoles and Indoles

Nickel-Catalyzed C−H Functionalization Using A Non-directed Strategy

Mechanism of Nickel(II)-Catalyzed C(2)–H Alkynylation of Indoles with Alkynyl Bromide

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