β ‐Keto Amides: A Jack‐of‐All‐Trades Building Block in Organic Chemistry

A novel acenaphthoimidazolyidene oxazolinic palladium complex and its efficient catalysis in Suzuki-Miyaura cross-coupling reactions of N-acyl-glutarimides via N-C cleavage

Herein, we synthesized a new Pd-N-heterocyclic carbene (Pd-NHC) complex that featured an acenaphthoimidazolylidene (AnIm) skeleton and 2-phenyl-2-oxazoline. This catalyst exhibited extremely high efficiency in Suzuki-Miyaura couplings between N-acyl-glutarimides and organoboronic acids, affording various aryl ketones in excellent yields with a broad substrate scope and wide functional group compatibility. Notably, the reactions were completed in just 5 hours with only 0.5 mol% of catalyst. In addition, this catalytic system also enables the efficient synthesis of functional molecular intermediates. The catalyst, designed through the synergistic integration of a throw-away ligand and an extended conjugated NHC system, further demonstrates its remarkable potential.

Enantioselective Spirocyclization of Pd-Enolates and Isocyanates

An enantioselective cyclization of Pd-enolates and isocyanates to form spirocyclic γ-lactams is reported. This reaction proceeds under mild reaction conditions and utilizes a novel Meldrum's acid derivative to achieve catalyst turnover, delivering enantioenriched products in up to 97% yield and 96% ee. Preliminary mechanistic investigations suggest that the reaction may proceed via the formation of higher-order species.

BF3·Et2O-promoted unconventional reactions of 2-oxoaldehyde: access to 4-amidooxazoles and β-keto amides/sulphonamides

This study investigates the potential of boron trifluoride etherate (BF3·OEt2) to trigger unprecedented reactions of 2-oxoaldehydes with nitriles and amides/sulphonamides. In contrast to the mechanism in conventional reactions, the α-carbonyl group in 2-oxoaldehydes induces a cyclization pathway to be followed when reacting with nitriles, yielding 4-amidooxazoles. Additionally, reactions with weak nucleophiles produce β-keto amides/sulphonamides. BF3·OEt2 catalysis offers a novel, efficient, and operationally simple synthetic route to these valuable compounds, showcasing the versatility of boron Lewis acids in organic transformations.

Research on transition metals for the multicomponent synthesis of benzo-fused γ-lactams

Benzo-fused γ-lactams are fundamental in medicinal chemistry, acting as essential elements for various therapeutic agents due to their structural adaptability and capability to enhance biological activity. In their synthesis, transition metals play a pivotal role as catalysts, offering more efficient alternatives to traditional methods by facilitating C-N bond formation through mechanisms like intramolecular coupling. Recent advances have especially spotlighted transition-metal-catalyzed C-H amination reactions for directly converting C(sp2)-H to C(sp2)-N bonds, streamlining the creation of these compounds. Furthermore, biocatalytic approaches have emerged, providing asymmetric synthesis of lactams with high yield and enantioselectivity. This review examined the transition metal-catalyzed synthesis techniques for producing benzo-fused γ-lactams, marking a significant leap in organic synthesis by proposing more effective, selective, and greener production methods. It serves as a valuable resource for researchers in the fields of transition metal catalysts and those engaged in synthesizing these lactams.

Asymmetric Synthesis of β-Ketoamides by Sulfonium Rearrangement

The synthesis of enantioenriched α-substituted 1,3-dicarbonyls remains a contemporary challenge in synthesis due to their tendency to undergo racemization via keto-enol tautomerization. Herein, we report a method to access enantioenriched β-ketoamides by a chiral sulfinimine-mediated [3,3]-sigmatropic sulfonium rearrangement. The transformation displays good chirality transfer, as well as excellent chemoselectivity and functional group tolerance. Diastereoselective reduction of the ketone moiety, also achievable in one-pot fashion, affords enantioenriched β-hydroxyamides.

Spiroannulations of β-Ketothioamides with Bromoenals via Selective C-Michael Addition and S-Michael Addition-Triggered Cascade Reactions

A spiroannulation reaction of β-ketothioamides with aromatic β-bromoenals and aromatic α-bromoenals via selective C-Michael addition and S-Michael addition-triggered cascade reactions has been developed. This protocol provides a novel and rapid approach for the synthesis of substituted spirothiopyran and spirothiophene derivatives under mild conditions with moderate to good yields and a broad substrate scope.

Allenamides as a Powerful Tool to Incorporate Diversity: Thia-Michael Lipidation of Semisynthetic Peptides and Access to β-Keto Amides

Lipopeptides are an important class of biomolecules for drug development. Compared with conventional acylation, a chemoselective lipidation strategy offers a more efficient strategy for late-stage structural derivatisation of a peptide scaffold. It provides access to chemically diverse compounds possessing intriguing and non-native moieties. Utilising an allenamide, we report the first semisynthesis of antimicrobial lipopeptides leveraging a highly efficient thia-Michael addition of chemically diverse lipophilic thiols. Using chemoenzymatically prepared polymyxin B nonapeptide (PMBN) as a model scaffold, an optimised allenamide-mediated thia-Michael addition effected rapid and near quantitative lipidation, affording vinyl sulfide-linked lipopeptide derivatives. Harnessing the utility of this new methodology, 22 lipophilic thiols of unprecedented chemical diversity were introduced to the PMBN framework. These included alkyl thiols, substituted aromatic thiols, heterocyclic thiols and those bearing additional functional groups (e.g., amines), ultimately yielding analogues with potent Gram-negative antimicrobial activity and substantially attenuated nephrotoxicity. Furthermore, we report facile routes to transform the allenamide into a β-keto amide on unprotected peptides, offering a powerful "jack-of-all-trades" synthetic intermediate to enable further peptide modification.

Switchable Enantio- and Diastereoselective Michael Additions of β-Keto Amides to Nitroolefins: Crystallization-Based Inversion of Kinetic Stereocontrol

Asymmetric catalytic reactions rely on chiral catalysts that induce highly ordered transition states capable of imparting stereoselectivity in the bond-forming step(s). Productive deviations from this paradigm are rare yet hold the potential for accessing different stereoisomers using the same catalyst. Here, we present an enantio- and diastereoselective Michael addition of β-keto amides to nitroolefin electrophiles proceeding via an unusual scenario where the kinetic diastereocontrol imparted by the catalyst may be overridden by crystallization to provide the complementary stereoisomer of the product.

Chemoselective α-Trifluoroacetylation of Amides Using Highly Electrophilic Trifluoroacetic Anhydrides and 2,4,6-Collidine

Chemoselective α-acylation of tertiary amides proceeded with highly electrophilic acid anhydrides and weak bases under mild conditions. β-Ketoamides containing trifluoroacetyl or perfluoroacyl groups were selectively obtained even in the presence of other functional groups such as ketone, ester, etc. Density functional theory calculations suggest that 1-acyloxyenamine is the key intermediate for the chemoselective α-acylation.

Simple purification of small-molecule-labelled peptides via palladium enolate formation from β-ketoamide tags

Palladium enolates derived from β-ketocarbonyl compounds serve as key intermediates in various catalytic asymmetric reactions. We found that the palladium enolate formed from β-ketoamide is stable in air and moisture and we applied this property to develop a peptide purification system using β-ketoamide as a small affinity tag in aqueous media. A solid-supported palladium complex successfully captured β-ketoamide-tagged molecules as palladium enolates and released them in high yield upon acid treatment. Optimum conditions for the catch and release of tagged peptides from a mixture of untagged peptides were established. To demonstrate the value of this methodology in identifying the binding site of a ligand to its target protein, we purified and identified a peptide containing the ligand-binding site from the tryptic digest of cathepsin B labelled with a covalent cathepsin B inhibitor containing a β-ketoamide tag.

Synthesis of N-[1-(2-Acetyl-4,5-dimethoxyphenyl)propan-2-yl]benzamide and Its Copper(II) Complex

This paper represents a convenient method for the synthesis of N-[1-(2-acetyl-4,5-dimethoxyphenyl)propan-2-yl]benzamide and its Cu(II) complex. In silico analysis predicted spasmolytic activity for the compound. Based on the in silico calculations, the importance of the predicted ketoamide, and our previous experiments, we synthesized the ketoamide via ortho-acylation of N-[1-(3,4-dimethoxyphenyl)propan-2-yl]benzamide with acetic anhydride in polyphosphoric acid. We applied the title ketoamide in reaction with Cu(II) varying the solvents. We found that the reaction leads to the formation of a coordination compound when the ligand dissolved in DMSO reacts with a water solution of CuCl₂ in an alkaline environment in a molar ratio M : L : OH^- = 1 : 2 : 2. The structures of the new compounds are discussed based on their melting points, IR, ¹H, ¹³C NMR and Raman spectral data.