One-pot transition-metal free transamidation to sterically hindered amides

Guo, Weijie; Huang, Jingjun; Wu, Huan; Liu, Tingting; Luo, Zhongfeng; Jian, Junsheng; Zhang, Zhuo

doi:10.1039/c8qo00591e

Cited by 59 publications

(20 citation statements)

References 81 publications

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“…Based on the control experiments, our previous reports– and N ‐acyl‐tert‐butyl‐carbamates favoring ground‐state destabilization, we hypothesized that the first step is a transamidation . Amide 1 a was attacked by nucleophilic o ‐bromoaniline to form corresponding transamidation product 4 a with the regeneration of the CsF catalyst under base‐free conditions; then, the second step is a transition‐metal catalyzed cyclization, which is known in the Cu‐catalyzed C−X bond transformation literature.…”

Section: Methodsmentioning

confidence: 99%

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Cesium Fluoride and Copper‐Catalyzed One‐Pot Synthesis of Benzoxazoles via a Site‐Selective Amide C−N Bond Cleavage

Luo

et al. 2019

Adv Synth Catal

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We report herein a two-step one-pot strategy for the synthesis of benzoxazoles from amides by using cesium fluoride/copper as catalysts. This approach involves the in situ generation of acyl fluorides from the corresponding amides, and the acyl fluorides undergo transamidation and cyclization to give benzoxazoles in good yields. In this work, the amide CÀ N bonds are activated by CsF to form the acyl fluoride intermediates, which further react with o-bromoanilines to efficiently yield benzoxazoles. Notably, this methodology demonstrates a broad substrate scope, as primary/secondary benzamides are well tolerated, and this process might facilitate the development of one-pot transformations of amides. Scheme 5. Control experiments. Scheme 6. Preliminary mechanism studies. Scheme 7. Scale-up of the one-pot reaction.

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Section: Methodsmentioning

confidence: 99%

“…Our group has already reported that CsF can react with amide bonds to form the corresponding acyl fluorides by site‐selective C−N bond cleavage, as mentioned above –. Thus, we hypothesized that this in situ‐ generated acyl fluoride could be utilized in the synthesis of benzoxazoles (Scheme c).…”

Section: Methodsmentioning

confidence: 99%

Cesium Fluoride and Copper‐Catalyzed One‐Pot Synthesis of Benzoxazoles via a Site‐Selective Amide C−N Bond Cleavage

Luo

et al. 2019

Adv Synth Catal

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“…In 2018, they reported an impressive one-pot, transition-metal-free transami-dation of primary amides via a cesium fluoride catalyzed pathway (Scheme 27). 54 In this protocol, the primary amide is first converted via site-selective N-tert-butoxycarbonylation into twisted N,N-Boc 2 -amides (see also Scheme 19), followed by CsF-catalyzed transamidation to form the amide products in excellent yields. Notably, the method is compatible with various functional groups and steric hindrance owing to the mild conditions for amide formation.…”

Section: Tandem Transamidationsmentioning

confidence: 99%

Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage

Szostak

2020

Synthesis

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In the past several years, tremendous advances have been made in non-classical routes for amide bond formation that involve transamidation and amidation reactions of activated amides and esters. These new methods enable the formation of extremely valuable amide bonds via transition-metal-catalyzed, transition-metal-free, or metal-free pathways by exploiting chemoselective acyl C–X (X = N, O) cleavage under mild conditions. In a broadest sense, these reactions overcome the formidable challenge of activating C–N/C–O bonds of amides or esters by rationally tackling nN → π*C=O delocalization in amides and nO → π*C=O donation in esters. In this account, we summarize the recent remarkable advances in the development of new methods for the synthesis of amides with a focus on (1) transition-metal/NHC-catalyzed C–N/C–O bond activation, (2) transition-metal-free highly selective cleavage of C–N/C–O bonds, (3) the development of new acyl-transfer reagents, and (4) other emerging methods.1 Introduction2 Transamidation of Amides2.1 Transamidation by Metal–NHC Catalysis (Pd–NHC, Ni–NHC)2.2 Transition-Metal-Free Transamidation via Tetrahedral Intermediates2.3 Reductive Transamidation2.4 New Acyl-Transfer Reagents2.5 Tandem Transamidations3 Amidation of Esters3.1 Amidation of Esters by Metal–NHC Catalysis (Pd–NHC, Ni–NHC)3.2 Transition-Metal-Free Amidation of Esters via Tetrahedral Intermediates3.3 Reductive Amidation of Esters4 Transamidations of Amides by Other Mechanisms5 Conclusions and Outlook

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“…Zeng and co-workers developed a one-pot activation of amide by its transformation to a sterically hindered tertbutyl dicarbonate (Scheme 23), that induced a twisting of the amide (see Scheme 1, B). 54 Scheme 23 One-pot transamidation to sterically hindered amides 54 Cesium fluoride was employed as catalyst for the in situ transformation of Boc-activated amide 136 to the corresponding acyl fluoride 138, which can be trapped by a variety of amines (Scheme 23). The conditions are mild, with high functional group and steric tolerance.…”

Section: Special Topic Synthesismentioning

confidence: 99%

Amide Synthesis by Transamidation of Primary Carboxamides

Marković

2020

Synthesis

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The amide functionality is one of the most important and widely used groups in nature and in medicinal and industrial chemistry. Because of its importance and as the actual synthetic methods suffer from major drawbacks, such as the use of a stoichiometric amount of an activating agent, epimerization and low atom economy, the development of new and efficient amide bond forming reactions is needed. A number of greener and more effective strategies have been studied and developed. The transamidation of primary amides is particularly attractive in terms of atom economy and as ammonia is the single byproduct. This review summarizes the advancements in metal-catalyzed and organocatalyzed transamidation methods. Lewis and Brønsted acid transamidation catalysts are reviewed as a separate group. The activation of primary amides by promoter, as well as catalyst- and promoter-free protocols, are also described. The proposed mechanisms and key intermediates of the depicted transamidation reactions are shown.1 Introduction2 Metal-Catalyzed Transamidations3 Organocatalyzed Transamidations4 Lewis and Brønsted Acid Catalysis5 Promoted Transamidation of Primary Amides6 Catalyst- and Promoter-Free Protocols7 Conclusion

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One-pot transition-metal free transamidation to sterically hindered amides

Abstract: A highly efficient one-pot transamidation of primary amides has been developed under transition-metal free conditions, generating a variety of amides including hindered amides in good yield (up to 86%) catalyzed by CsF.

Cited by 59 publications

References 81 publications

Cesium Fluoride and Copper‐Catalyzed One‐Pot Synthesis of Benzoxazoles via a Site‐Selective Amide C−N Bond Cleavage

Cesium Fluoride and Copper‐Catalyzed One‐Pot Synthesis of Benzoxazoles via a Site‐Selective Amide C−N Bond Cleavage

Non-Classical Amide Bond Formation: Transamidation and Amidation of Activated Amides and Esters by Selective N–C/O–C Cleavage

Amide Synthesis by Transamidation of Primary Carboxamides

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