Nickel-Mediated Enantiospecific Silylation via Benzylic C–OMe Bond Cleavage

Balakrishnan, Venkadesh; Murugesan, Vetrivelan; Chindan, Bincy; Rasappan, Ramesh

doi:10.1021/acs.orglett.0c04316

Cited by 36 publications

(26 citation statements)

References 59 publications

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“…Anionic nickelates derived from silyl anions have more recently been implicated in the enantiospecific silylation of benzyl methyl ethers. 56 57 31 P NMR spectroscopy studies support that an Ni(0)-ate complex of the constitution [L n Ni–SiMe 3 ] – [MgI(solv)] + is formed on addition of Me 3 SiMgI(TMEDA) to NiBr 2 (diglyme)/PCy 3 , or by direct treatment of the Ni(0) precursor, Ni(PCy 3 ) 2 , with Me 3 SiMgI(TMEDA). This same signal is also observed in the reaction mixture, and cyclic voltammetry and UV-Vis spectroscopy studies suggest that this Ni(0)-ate is the predominant resting state.…”

Section: Anionic Nickelatesmentioning

confidence: 93%

Mechanisms of the Nickel-Catalysed Hydrogenolysis and Cross-Coupling of Aryl Ethers

Borys¹,

Hevia²

2022

Synthesis

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The Ni-catalysed hydrogenolysis and cross-coupling of aryl ethers has emerged as a powerful synthetic tool to transform inert phenol-derived electrophiles into functionalised aromatic molecules. This has attracted significant interest due to its potential to convert the lignin fraction of biomass into chemical feedstocks, or to enable orthogonal reactivity and late-stage synthetic modification. Although the scope of nucleophiles employed, and hence the CC and Cheteroatom bonds that can be forged, has expanded significantly since Wenkert’s seminal work in 1979, mechanistic understanding on how these reactions operate is still uncertain since the comparatively inert CarylO bond of aryl ethers challenge the involvement of classical mechanisms involving direct oxidative addition to Ni(0). In this review, we document the different mechanisms that have been proposed in the Ni-catalysed hydrogenolysis and cross-coupling of aryl ethers. These include: i) direct oxidative addition; ii) Lewis acid assisted CO bond cleavage; iii) anionic nickelates, and; iv) Ni(I) intermediates. Experimental and theoretical investigations by numerous research groups have generated a pool of knowledge that will undoubtably facilitate future discoveries in the development of novel Ni-catalysed transformations of aryl ethers.

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Section: Anionic Nickelatesmentioning

confidence: 93%

Mechanisms of the Nickel-Catalysed Hydrogenolysis and Cross-Coupling of Aryl Ethers

Borys¹,

Hevia²

2022

Synthesis

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“…Therefore, the coordinating ability of the oxygen leaving group is particularly important for the stereoretentive C(sp 3 )–O bond cleavage. To address the challenges of C–O bond activation of benzylic ether and alcohol, a series of ingenious catalysis designs were realized, which led to a diverse set of powerful transformations under nickel, − ,− ,,,,,− palladium, ,, iron, ,− ruthenium, , and chromium ,, catalysis.…”

Section: Mechanism and Controlling Factors Of Stereospecificity In Ni...mentioning

confidence: 99%

Mechanism and Selectivity Control in Ni- and Pd-Catalyzed Cross-Couplings Involving Carbon–Oxygen Bond Activation

Zhang

Hong

2021

Acc. Chem. Res.

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Conspectus Transition-metal-catalyzed C–O bond activation provides a useful strategy for utilizing alcohol- and phenol-derived electrophiles in cross-coupling reactions, which has become a research field of active and growing interest in organic chemistry. The synergy between computation and experiment elucidated the mechanistic model and controlling factors of selectivities in these transformations, leading to advances in innovative C–O bond activation and functionalization methods. Toward the rational design of C–O bond activation, our collaborations with the Jarvo group bridged the mechanistic models of C(sp2)–O and C(sp3)–O bond activations. We found that the nickel catalyst cleaves the benzylic and allylic C(sp3)–O bonds via two general mechanisms: the stereoinvertive SN2 back-side attack model and the stereoretentive chelation-assisted model. These two models control the stereochemistry in a wide array of stereospecific Ni-catalyzed cross-coupling reactions with benzylic or allylic alcohol derivatives. Because of the catalyst distortion, the ligands can differentiate the competing stereospecific C(sp3)–O bond activations. The PCy3 ligand interacts with nickel mainly through σ-donation, and the Ni(PCy3) catalyst can undergo facile bending of the substrate–nickel–ligand angle, which favors the stereoretentive benzylic C–O bond activation. The N-heterocyclic carbene SIMes ligand has additional d(metal)–p(ligand) back-donation with nickel, which leads to an extra energy penalty for the same angle bending. This results in the preference of stereoinvertive benzylic C–O bond activation under Ni/SIMes catalysis. In addition to ligand control, a Lewis acid can increase the selectivity for stereoinvertive C(sp3)–O activation by stabilizing the SN2 back-side attack transition state. The oxygen leaving group complexes with the MgI2 Lewis acid in the stereoinvertive activation, leading to the exclusive stereoinvertive Kumada coupling of benzylic ethers. We also identified that the competing C(sp3)–O bond activation models have noticeable differences in charge separation. This leads to the solvent polarity control of the stereospecificity in C(sp3)–O activations. Low-polarity solvents favor the neutral stereoretentive C–O bond activation, while high-polarity solvents favor the zwitterionic stereoinvertive cleavage. In sharp contrast to the nickel catalysts, the C(sp2)–O bond activation under palladium catalysis mainly proceeds via the classic three-membered ring oxidative addition mechanism instead of the chelation-assisted mechanism. This is due to the lower oxophilicity of palladium, which disfavors the oxygen coordination in the chelation-assisted-type activation. The three-membered ring activation model selectively cleaves the weak C–O bond, resulting in the exclusive chemoselectivity of acyl C–O bond activation in Pd-catalyzed cross-coupling reactions with aryl carboxylic acid derivatives. This explains the overall acylation in the Pd-catalyzed Suzuki–Miyaura coupling with aryl esters. In collaboration wi...

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“…However, the undesired homocoupling of pyridinium salts and site selectivity in C–H abstraction must be addressed (Scheme d). As a part of our ongoing studies in nickel mediated cross-coupling reactions, − herein we describe the Ni/TBADT dual catalysis for the successful realization of coupling between alkyl aldehydes and benzylic pyridinium salts.…”

mentioning

confidence: 99%

C–H Alkylation of Aldehydes by Merging TBADT Hydrogen Atom Transfer with Nickel Catalysis

et al. 2021

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Catalyst controlled site-selective C−H functionalization is a challenging but powerful tool in organic synthesis. Polarity-matched and sterically controlled hydrogen atom transfer (HAT) provides an excellent opportunity for site-selective functionalization. As such, the dual Ni/photoredox system was successfully employed to generate acyl radicals from aldehydes via selective formyl C−H activation and subsequently cross-coupled to generate ketones, a ubiquitous structural motif present in the vast majority of natural and bioactive molecules. However, only a handful of examples that are constrained to the use of aryl halides are developed. Given the wide availability of amines, we developed a cross-coupling reaction via C−N bond cleavage using the economic nickel and TBADT catalyst for the first time. A range of alkyl and aryl aldehydes were cross-coupled with benzylic and allylic pyridinium salts to afford ketones with a broad spectrum of functional group tolerance. High regioselectivity toward formyl C−H bonds even in the presence of α-methylene carbonyl or αamino/oxy methylene was obtained.

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Nickel-Mediated Enantiospecific Silylation via Benzylic C–OMe Bond Cleavage

Cited by 36 publications

References 59 publications

Mechanisms of the Nickel-Catalysed Hydrogenolysis and Cross-Coupling of Aryl Ethers

Mechanisms of the Nickel-Catalysed Hydrogenolysis and Cross-Coupling of Aryl Ethers

Mechanism and Selectivity Control in Ni- and Pd-Catalyzed Cross-Couplings Involving Carbon–Oxygen Bond Activation

C–H Alkylation of Aldehydes by Merging TBADT Hydrogen Atom Transfer with Nickel Catalysis

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