Chromium-Catalyzed Activation of Acyl C–O Bonds with Magnesium for Amidation of Esters with Nitroarenes

Ling, Liang; Chen, Changpeng; Luo, Meiming; Zeng, Xiaoming

doi:10.1021/acs.orglett.9b00554

Cited by 55 publications

(34 citation statements)

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“…Hu and co-workers reported the use of a nickel catalyst for reductive amidation of esters using nitroarenes [22]. Similar reductive coupling reactions using chromium catalysts have also been recently reported by Zeng and co-workers [23]. Nickel has also been employed by Newman and co-workers for direct amidation of methyl esters at high reaction temperatures [24].…”

Section: Introductionmentioning

confidence: 53%

Solvent-Free Iron(III) Chloride-Catalyzed Direct Amidation of Esters

et al. 2020

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Amide functional groups are prominent in a broad range of organic compounds with diverse beneficial applications. In this work, we report the synthesis of these functional groups via an iron(iii) chloride-catalyzed direct amidation of esters. The reactions are conducted under solvent-free conditions and found to be compatible with a range of amine and ester substrates generating the desired amides in short reaction times and good to excellent yields at a catalyst loading of 15 mol%.

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Section: Introductionmentioning

confidence: 53%

Solvent-Free Iron(III) Chloride-Catalyzed Direct Amidation of Esters

et al. 2020

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“…The air-stable CrCl 3 salt displays similar reactivity to provide 3a (entry 3). 43,44 However, the amidation using other Cr complexes such as Cr(OAc) 3 , Cr(acac) 3 and Cr(CO) 6 did not proceed, and the color of the solutions was not changed to black (entries 4-6).…”

Section: Resultsmentioning

confidence: 99%

Chromium-Catalyzed Ligand-Free Amidation of Esters with Anilines

Chen

Ling

Luo

et al. 2020

Bulletin of the Chemical Society of Japan

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Advance Publication is a service for online publication of manuscripts prior to releasing fully edited, printed versions. Entire manuscripts and a portion of the graphical abstract can be released on the web as soon as the submission is accepted. Note that the Chemical Society of Japan bears no responsibility for issues resulting from the use of information taken from unedited, Advance Publication manuscripts.

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“…NMR spectra and physical properties matched those reported in literature. 33 N-methyl-N-phenylfuran-2-carboxamide (5c) Amide 5c was synthesized using a modified procedure B, starting with 2-furoyl chloride (0.52 mL, 5.25 mmol) and aniline (0.48 mL, 5.0 mmol) as the starting materials. The product was purified via recrystallization from hot EtOH to yield an off-yellow, crystalline solid, 43% (0.40 g).…”

Section: -Fluoro-n-phenylbenzamide (5a)mentioning

confidence: 99%

Reverse Polarity Reductive Functionalization of Tertiary Amides via a Dual Iridium-Catalyzed Hydrosilylation and Single Electron Transfer Strategy

et al. 2020

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A new strategy for the mild generation of synthetically valuable α-amino radicals from robust tertiary amide building blocks has been developed. By combining Vaska's complex-catalyzed tertiary amide reductive activation and photochemical single electron reduction into a streamlined tandem process, metastable hemiaminal intermediates were successfully transformed into nucleophilic α-amino free radical species. This umpolung approach to such reactive intermediates was exemplified through coupling with an electrophilic dehydroalanine acceptor, resulting in the synthesis of an array of α-functionalized tertiary amine derivatives, previously inaccessible from the amide starting materials. The utility of the strategy was expanded to include secondary amide substrates, intramolecular variants and late stage functionalization of an active pharmaceutical ingredient. DFT analyses were used to establish the reaction mechanism and elements of the chemical system that were responsible for the reaction's efficiency. Scheme 1. α-Functionalization strategies for amine synthesis from tertiary amides Scheme 3. Optimization studies for (A) Vaska's catalyzed amide hydrosilylation. (B) The photocatalytic reductive coupling of the silyl hemiaminal intermediate with DHA derivative. stituted structures delivered tertiary amine products, although a steric increase vs. reaction efficiency trend was observed. 19 Intramolecular Cyclization. We recognized the opportunity that this tandem amide activation protocolthrough tethering an alkene acceptor to the alkyl chain of the amide starting material-could be suitably leveraged towards the synthesis of complex heterocyclic amine frameworks. Accordingly, model substrates bearing a pendant α,β-unsaturated ester (1s-1t) were prepared, but initial studies demonstrated that these motifs did not readily undergo hydrosilylation using Vaska's catalyst (only around 80% conversion was achieved after 8 hours of reaction time), and furthermore significant quantities of over reduction side-product were isolated following the photocatalytic step. 20 Nevertheless, these initial challenges were circumvented when a derivative of Vaska's complex bearing triphenylphosphite ligands-previously reported by Nagashima 21-was employed in the hydrosilylation step instead (Scheme 5). Pleasingly, clean conversion to a stable silyl hemiaminal species was achieved within one hour, and subsequent subjection to the optimized photoredox conditions delivered the desired cyclic pyrrolidine (4s) and piperidine (4t) products in good yields. Scheme 5. Extension of the Vaska-photoredox system for reductive cyclization of tertiary amides Secondary Amide Activation. Recent endeavors by Chida and Sato, and Huang have demonstrated the utility of [Ir(COE)2Cl]2 complex in conjunction with Et2SiH2 reductant for the nucleophilic reductive functionalization of secondary amide building blocks, affording the corresponding α-branched secondary amine products. 4e,f Scheme 6. Reverse polarity, photocatalytic reductive functionalization of seconda...

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Chromium-Catalyzed Activation of Acyl C–O Bonds with Magnesium for Amidation of Esters with Nitroarenes

Cited by 55 publications

References 50 publications

Solvent-Free Iron(III) Chloride-Catalyzed Direct Amidation of Esters

Solvent-Free Iron(III) Chloride-Catalyzed Direct Amidation of Esters

Chromium-Catalyzed Ligand-Free Amidation of Esters with Anilines

Reverse Polarity Reductive Functionalization of Tertiary Amides via a Dual Iridium-Catalyzed Hydrosilylation and Single Electron Transfer Strategy

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