ChemInform Abstract: Rhodium(III)‐Catalyzed Oxidative C—H Functionalization of Azomethine Ylides.

Zhen, Wencui; Wang, Fen; Zhao, Miao; Du, Zhengyin; Li, Xingwei

doi:10.1002/chin.201315163

Cited by 3 publications

(3 citation statements)

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“…238 In 2012, Li and co-workers also demonstrated that the azomethine group (273,274) may act as a potential removable directing group for the generation of formyl heteroarenes. 239 The oxidant Cu(OAc) 2 •H 2 O is crucial for the success of the reaction. Both acrylates and styrenes were suitable substrates in this transformation (Scheme 149).…”

Section: Arene−alkene Couplingmentioning

confidence: 99%

Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

et al. 2015

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Section: Arene−alkene Couplingmentioning

confidence: 99%

Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

et al. 2015

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“…13 To overcome the limitation of DGs in simple nucleophilic cyclization reactions, we designed azomethine imines as arene substrates that reacted with diverse selectivity (Scheme 5). 14 The oxidative coupling of benzaldehyde-derived azomethine imines with activated olefins occurred via C−H activation and C−N cleavage to give 1,2-dihydrophthalazines (Scheme 5a). Several intermediates were examined, and it was found that the reaction underwent initial oxidative olefination to give intermediate Int5, which was followed by rhodium-catalyzed reversible ring scission (retro-Michael addition) to generate protic hydrazone intermediate Int6.…”

Section: Dgs As Nucleophilesmentioning

confidence: 99%

Substrate Activation Strategies in Rhodium(III)-Catalyzed Selective Functionalization of Arenes

2015

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The possibility of developing new methods for the efficient construction of organic molecules via disconnections other than traditional functional group transformations has driven the interest in direct functionalization of C-H bonds. The ubiquity of C-H bonds makes such transformations attractive, but they also pose several challenges. The first is the reactivity and selectivity of C-H bonds. To achieve this, directing groups (DGs) are often installed that can enhance the effective concentration of the catalyst, leading to thermodynamically stable metallacyclic intermediates. However, the presence of a pendant directing group in the product is often undesirable and unnecessary. This may account for the limitation of applications of C-H functionalization reactions in more common and general uses. Thus, the development of removable or functionalizable directing groups is desirable. Another key problem is that the reactivity of the resulting M-C bond can be low, which may limit the scope of the coupling partners and hence limit the reaction patterns of C-H activation reactions. While the first Cp*Rh(III)-catalyzed C-H activation of arenes was reported only 7 years ago, significant progress has been made in this area in the past few years. We began our studies in this area in 2010, and we and others have demonstrated that diversified catalytic functionalization of arenes can be realized using Cp*Rh(III) complexes with high reactivity, stability, and functional group compatibility. This Account describes our efforts to solve some of these challenges using Rh(III) catalysis. We fulfilled our design and activation of the arene substrates by taking advantage of the nucleophilicity, electrophilicity, oxidizing potential, and properties of a participating ligand of the directing groups when the arenes are coupled with relatively reactive unsaturated partners such as alkenes and alkynes. These in situ funtionalizable roles of the DG allowed extensive chemical manipulation of the initial coupled product, especially in the construction of a diverse array of heterocycles. In the coupling of arenes with polar coupling partners, the polar Rh(III)-C(aryl) bond showed higher reactivity as both an organometallic reagent and a nucleophilic aryl source. The polar coupling partners were accordingly activated by virtue of umpolung, ring strain, and rearomatization. All of these transformations have been made possible by integration of the higher reactivity, stability, and compatibility of Rh(III)-C bonds into catalytic systems. We have demonstrated that to date some of these transformations can be achieved only under rhodium catalysis. In addition, by means of stoichiometric reactions, we have gained mechanistic insights into the interactions between the Rh-C bond and the other coupling partners, which have opened new avenues in future direct C-H functionalization reactions.

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“…32−34 Recently, extensive and innovative studies have investigated Rh(III)catalyzed C−H functionalization. 10,14,24,35,36 When strong oxidative directing groups are used in rhodium catalysis, an alternative Rh(III)/Rh(V) catalytic cycle may be more favorable than the Rh(III)/Rh(I) catalytic cycle. Some Rh(V) intermediates and their generation/transformation have recently been investigated in depth by theoretical calculations, 37−40 and they have attracted interest from experimental chemists.…”

Section: ■ Introductionmentioning

confidence: 99%

Origin of Regiochemical Control in Rh(III)/Rh(V)-Catalyzed Reactions of Unsaturated Oximes and Alkenes to Form Pyrdines

Chen

et al. 2019

ACS Catal.

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The Rh(III)-catalyzed reactions of α,β-unsaturated oximes with alkenes are versatile methods for the synthesis of pyridines. Density functional theory (DFT) calculations reported here reveal the detailed mechanism and origins of selectivity in this reaction. The Rh(III)/Rh(V)/Rh(I) catalytic cycle was found to be more favorable than the previously proposed Rh(III)/Rh(I)/ Rh(III) catalytic cycle. The Rh(III)/Rh(V)/Rh(I) catalytic cycle involves C−H activation, alkene insertion, deprotonation, oxime migratory oxidative addition, nitrene insertion, 1,5-hydrogen shift, and β-hydride elimination to give the pyridine product and form a Rh(I) species. Subsequent oxidation by Ag+ regenerates the Rh(III) catalyst. Reductive elimination from a alkyl-Rh(III) species is predicted to be difficult, so that the Rh(III)/Rh(I)/ Rh(III) catalytic cycle can be excluded. The reactivities of oxime ethers and oxime esters are compared. The oxime ester acts as both a directing group and an internal oxidant. In this reaction, the N−O bond is activated by the pivalate, and migratory oxidative addition onto the Rh(III) species generates the corresponding Rh(V) nitrene complex. However, in the absence of the pivalate on the oxime ether, the activation energy for oxidative addition is much higher. The reactivity was analyzed by NPA charge calculations, comparison of the N−O bond orders, and the bond dissociation energies. The calculations also explain the regioselectivity of alkene insertion, which is shown to be an electronic effect rather than a steric effect.

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ChemInform Abstract: Rhodium(III)‐Catalyzed Oxidative C—H Functionalization of Azomethine Ylides.

Cited by 3 publications

References 1 publication

Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

Oxidative Coupling between Two Hydrocarbons: An Update of Recent C–H Functionalizations

Substrate Activation Strategies in Rhodium(III)-Catalyzed Selective Functionalization of Arenes

Origin of Regiochemical Control in Rh(III)/Rh(V)-Catalyzed Reactions of Unsaturated Oximes and Alkenes to Form Pyrdines

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