Iron‐Catalyzed C−H Activation with Propargyl Acetates: Mechanistic Insights into Iron(II) by Experiment, Kinetics, Mössbauer Spectroscopy, and Computation

Mo, Jiayu; Müller, Thomas; Oliveira, João C. A.; Demeshko, Serhiy; Meyer, Franc; Ackermann, Lutz

doi:10.1002/anie.201904110

Cited by 33 publications

(24 citation statements)

References 68 publications

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“…In the Hammett curve, lg(k X /k H ) is linear with σ, and the negative value of ρ (-1.07) indicates that the reaction is facilitated by electron-donating groups (see Supporting information for details). [15] Moreover, density functional theory (DFT) calculations were performed to clarify the regioselectivity of the reaction (Figure 1; for the details see Supporting Information). The initiation of the reaction involves the protonation of the alkynyl of 1a to form a cationic intermediate I1, where the electrophilic ortho-cyclization process between the carbon cation C3 and C1 takes place via transition state TS1-2 to afford I2.…”

Section: Scheme 4 Gram-scale Experiments and Synthetic Application Of 3amentioning

confidence: 99%

Metal‐Free Catalyzed Cyclization of N‐Methoxybenzamides to Construct Quaternary Carbon‐Containing Isoindolinones

et al. 2021

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Quaternary carbe | Density functional theory | Annulation | Alkynes | Synthetic methods Through the intramolecular cyclization of N-methoxybenzamides, a simple and efficient method for constructing valuable isoindolinones under metal-free conditions was developed. The reaction was featured by employing low-cost catalyst, simple operation, 100% atomic economy and excellent regioselectivity. Moreover, a detailed computational study on the reaction system has been performed to clarify the mechanism. This protocol tolerated a variety of functional groups and provided a metal-free protocol for the synthesis of chromane-or tetrahydroquinoline-fused isoindolinones in good yields.

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Section: Scheme 4 Gram-scale Experiments and Synthetic Application Of 3amentioning

confidence: 99%

Metal‐Free Catalyzed Cyclization of N‐Methoxybenzamides to Construct Quaternary Carbon‐Containing Isoindolinones

et al. 2021

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“…More recently, iron-catalyzed, triazole-assisted C-H functionalization methodologies have been exploited in the presence of propargyl acetates 40 for the synthesis of highly decorated isoquinolone derivatives [72]. As previously discussed, only TAH DGs were able to promote the highly selective C-H/N-H annulation reaction.…”

Section: Iron-catalyzed C-h Functionalizations With Alkynes and Allenesmentioning

confidence: 99%

“…This approach presented a notable advantage with respect to recent removal protocols of the AQ DG that required the use of hazardous chemicals such as ozone and dimethylsulfide (DMS) (Scheme 23c) [73]. More recently, iron-catalyzed, triazole-assisted C-H functionalization methodologies have been exploited in the presence of propargyl acetates 40 for the synthesis of highly decorated isoquinolone derivatives [72]. As previously discussed, only TAH DGs were able to promote the highly selective C-H/N-H annulation reaction.…”

Section: Iron-catalyzed C-h Functionalizations With Alkynes and Allenesmentioning

confidence: 99%

Iron-Catalyzed C–H Functionalizations under Triazole-Assistance

Lanzi

Cera

2020

Molecules

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3d transition metals-catalyzed C-H bond functionalizations represent nowadays an important tool in organic synthesis, appearing as the most promising alternative to cross-coupling reactions. Among 3d transition metals, iron found widespread application due to its availability and benign nature, and it was established as an efficient catalyst in organic synthesis. In this context, the use of ortho-orientating directing groups (DGs) turned out to be necessary for promoting selective iron-catalyzed C-H functionalization reactions. Very recently, triazoles DGs were demonstrated to be more than an excellent alternative to the commonly employed 8-aminoquinoline (AQ) DG, as a result of their modular synthesis as well as the mild reaction conditions applied for their removal. In addition, their tunable geometry and electronics allowed for new unprecedented reactivities in iron-catalyzed C-H activation methodologies that will be summarized within this review. Scheme 2. Triazole-assisted C(sp 2 )-H arylation; (a) Aryl amides functionalizations; (b) Acrylamide functionalization; (c) Removal of TAM DG.The deprotection of TAM DG was carried out under acidic conditions, leading to ortho-arylated benzoic acid 5b in high yields (Scheme 2c). TAM DG was found applicable for C-H arylations of ferrocene derivatives 6 as well [42]. Again, the combination of diphosphine ligand dppe and 2,3dichlorobutane (2,3-DCB) as external oxidant was found essential for the transformation. The use of an in situ-formed Ar2Zn•MgBr2(TMEDA) organometallic base allowed for the conversion of amides 6a-b into racemic products 7a-b in good yields. Noteworthy, the use of a chiral ligand such as R,R-Scheme 2. Triazole-assisted C(sp 2 )-H arylation; (a) Aryl amides functionalizations; (b) Acrylamide functionalization; (c) Removal of TAM DG.The deprotection of TAM DG was carried out under acidic conditions, leading to ortho-arylated benzoic acid 5b in high yields (Scheme 2c). TAM DG was found applicable for C-H arylations of ferrocene derivatives 6 as well [42]. Again, the combination of diphosphine ligand dppe and Molecules 2020, 25, 1806 4 of 26 2,3-dichlorobutane (2,3-DCB) as external oxidant was found essential for the transformation. The use of an in situ-formed Ar 2 Zn•MgBr 2 (TMEDA) organometallic base allowed for the conversion of amides 6a-b into racemic products 7a-b in good yields. Noteworthy, the use of a chiral ligand such as R,R-chiraphos led to the formation of a planar chiral ferrocene derivative 7c with moderate enantiomeric ratio (Scheme 3). Molecules 2020, 25, x FOR PEER REVIEW 4 of 27 chiraphos led to the formation of a planar chiral ferrocene derivative 7c with moderate enantiomeric ratio (Scheme 3). Scheme 3. Iron-catalyzed C(sp 2 )-H arylation of ferrocenes aromatic rings with TAM DG.The activation of C(sp 3 )-H is generally more challenging than C(sp 2 )-H due to their lower acidity [43,44]. In analogy with previous reports on iron-catalyzed C(sp 3 )-H arylations enabled by 8-AQ DGs, TAM DG was found operative under similar conditions [...

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“…1a , left side) 17 , 18 . Inspired by these seminal works, various transition metal-catalyzed vinylic C–H annulation reactions with alkynes have been developed to prepare α-pyridones or α-pyrones, including ones catalyzed by Rh 19 – 24 , Ru 25 – 29 , Co 30 – 33 , Pd 34 – 36 , and Fe 37 , 38 catalysts. Despite these advances, important challenges remain, including: (1) typically high reaction temperatures (100–120 °C); (2) stoichiometric transition metal oxidants such as Cu(OAc) 2 or AgOAc are generally required to regenerate catalysts; (3) a highly selective divergent synthesis of α-pyridones and cyclic imidates (Fig.…”

Section: Introductionmentioning

confidence: 99%

“…1a, left side) 17,18 . Inspired by these seminal works, various transition metalcatalyzed vinylic C-H annulation reactions with alkynes have been developed to prepare α-pyridones or α-pyrones, including ones catalyzed by Rh [19][20][21][22][23][24] , Ru [25][26][27][28][29] , Co [30][31][32][33] , Pd [34][35][36] , and Fe 37,38 catalysts. Despite these advances, important challenges remain, including: (1) typically high reaction temperatures (100-120°C);…”

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confidence: 99%

Divergent rhodium-catalyzed electrochemical vinylic C–H annulation of acrylamides with alkynes

et al. 2021

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Abstractα-Pyridones and α-pyrones are ubiquitous structural motifs found in natural products and biologically active small molecules. Here, we report an Rh-catalyzed electrochemical vinylic C–H annulation of acrylamides with alkynes, affording cyclic products in good to excellent yield. Divergent syntheses of α-pyridones and cyclic imidates are accomplished by employing N-phenyl acrylamides and N-tosyl acrylamides as substrates, respectively. Additionally, excellent regioselectivities are achieved when using unsymmetrical alkynes. This electrochemical process is environmentally benign compared to traditional transition metal-catalyzed C–H annulations because it avoids the use of stoichiometric metal oxidants. DFT calculations elucidated the reaction mechanism and origins of substituent-controlled chemoselectivity. The sequential C–H activation and alkyne insertion under rhodium catalysis leads to the seven-membered ring vinyl-rhodium intermediate. This intermediate undergoes either the classic neutral concerted reductive elimination to produce α-pyridones, or the ionic stepwise pathway to produce cyclic imidates.

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Iron‐Catalyzed C−H Activation with Propargyl Acetates: Mechanistic Insights into Iron(II) by Experiment, Kinetics, Mössbauer Spectroscopy, and Computation

Cited by 33 publications

References 68 publications

Metal‐Free Catalyzed Cyclization of N‐Methoxybenzamides to Construct Quaternary Carbon‐Containing Isoindolinones

Metal‐Free Catalyzed Cyclization of N‐Methoxybenzamides to Construct Quaternary Carbon‐Containing Isoindolinones

Iron-Catalyzed C–H Functionalizations under Triazole-Assistance

Divergent rhodium-catalyzed electrochemical vinylic C–H annulation of acrylamides with alkynes

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