Ir(I)-catalyzed synthesis of N-substituted pyridones from 2-alkoxypyridines via C-O bond cleavage

Bi(III)-Catalyzed Michael Addition of Tautomerizable Heterocycles with α,β-Unsaturated Carbonyl Compounds: Regioselective Construction of C-N Bonds

A Bi(III)-catalyzed synthetic strategy for regioselective construction of C-N bonds via a simple Michael addition reaction is reported. A wide range of tautomerizable heterocycles such as benzoxazolones, benzothiazolones, benzimidazolinones, indolinones, and 2-pyridones along with α,β-unsaturated carbonyls (ketones and esters) are employed to create a library of corresponding N-alkylated derivatives exclusively. High regioselectivity, high atom economy, and the participation of a range of tautomerizable heterocycles highlight the uniqueness and generality of the developed methodology.

Palladium-Catalyzed anti-Michael-Type Hydroamination of N-(Quinolin-8-yl)acrylamide with 2-Pyridones

Here we report a palladium-catalyzed anti-Michael-type hydroamination of N-(quinolin-8-yl)acrylamide with 2-pyridones. The use of a palladium catalyst enables the α-addition of 2-pyridones, resulting in the formation of a range of N-substituted 2-pyridone carboxamides with yields ranging from 10% to 80%. Derivatization of the products highlights the utility of this transformation. Preliminary mechanistic investigations suggest that the reaction proceeds through the direct addition of a nitrogen atom of 2-pyridones, ruling out other pathways such as O-to-N-alkyl migration.

P(NMe2)3-Mediated Regioselective N-Alkylation of 2-Pyridones via Direct Deoxygenation of α-Keto Esters

A practical and regioselective direct N-alkylation of 2-pyridones is enabled by use of α-keto esters in the P(NMe2)3-mediated deoxygenation process. The reaction proceeds under mild conditions to produce N-alkylated 2-pyridones with high selectivity and generality, and the protocol is shown to be applicable for the scale-up synthesis, which makes it promising for practical applications.

Recent Progresses in the Catalytic Stereoselective Dearomatization of Pyridines

1,2- and 1,4-dihydropyridines and N-substituted 2-pyridones are very important structural motifs due to their synthetic versatility and vast presence in a variety of alkaloids and bioactive molecules. In this article, we gather and summarize the catalytic and stereoselective synthesis of partially hydrogenated pyridines and pyridones via the dearomative reactions of pyridine derivatives up to mid-2023. The material is fundamentally organized according to the type of reactivity (electrophilic/nucleophilic) of the pyridine nucleus. The material is further sub-divided taking into account the nucleophilic species when dealing with electrophilic pyridines and considering the reactivity manifold of pyridine derivatives behaving as nucleophiles at the nitrogen site. The latter more recent approach allows for an unconventional entry to chiral N-substituted 2- and 4-pyridones in non-racemic form.

Direct C(3)5-H Polyfluoroarylation of 2-Amino/alkoxy Pyridines Enabled by a Transient and Electron-deficient Palladium Intermediate

Herein, we present an unprecedented azine-limited C5-H polyfluoroarylation of 2-aminopyridines enabled by a transient and electron-deficient perfluoroaryl-Pd species via C-H/C-H coupling. The protocol further allows C3(5)-H polyfluoroarylation of 2-alkoxypyridines guided by sterics and electronics for the first time. The late-stage C-H functionalization of drugs, drug derivatives, and natural product derivatives and synthesis of C5-aryl drug derivatives further demonstrated the method's utility. The preliminary mechanistic studies reveal that the synergistic combination of the bulky yet electrophilic perfluoroaryl-Pd species and the partial nucleophilicity of the C5-position of 2-amino/alkoxy-pyridines is the origin of reactivity and selectivity. Importantly, the first experimental evidence for the role of diisopropyl sulfide is provided.

Synthesis of N-Substituted 3-Amino-2-pyridones

Pyridones are versatile building blocks in organic synthesis and a privileged motif in drug discovery. However, N-substituted 2-pyridones bearing an α-tertiary carbon, cyclopropyl, or heterocycle off of the pyridone nitrogen atom remain challenging to prepare. Herein, we describe the efficient synthesis of a large variety of N-substituted 2-pyridones from ethyl nitroacetate and readily available primary amine building blocks, which can be utilized on a large scale and in parallel medicinal chemistry applications.

Recent advances in catalytic asymmetric [1,3]-rearrangement reactions

This review covering the recent advances of asymmetric 1,3-rearrangement reactions is divided into four different fields, including transition metal catalysis, nucleophilic catalysis, Brønsted acid catalysis and Lewis acid catalysis.

Selective approach to N-substituted tertiary 2-pyridones

Commercially available 2-hydroxypyridines are converted into enantiomerically enriched allylic 2-pyridones with elusive N-substituted tertiary carbon by means of Pd-catalyzed allylic amination of vinyl cyclic carbonates.

Rhodium-Catalyzed Dearomative Rearrangement of 2-Oxypyridines with Cyclopropenes: Access to N-Alkylated 2-Pyridones

A rhodium-catalyzed dearomative O-to-N rearrangement reaction of 2-oxypyridines has been developed by using cyclopropenes as the carbene precursors. This protocol features broad substrate scope and mild reaction conditions, providing a...

A Mild and Highly Diastereoselective Preparation of N-Alkenyl-2-Pyridones via 2-Halopyridinium Salts and Aldehydes

An experimentally simple one-pot preparation of N-alkenyl-2-pyridones is reported. The reaction features mild conditions using readily available 2-halopyridinium salts and aldehydes. N-Alkenyl-2-pyridone formation proceeds with high diastereoselectivity, and a wide range of aldehyde reaction partners is tolerated. Pyridone products are also amenable to further manipulation, including conversion to N-alkyl pyridones and polycyclic ring systems.

Visible-light-promoted selective O-alkylation of 2-pyridones with α-aryldiazoacetates

A visible-light-promoted O-H insertion reaction between 2-pyridones and α-aryldiazoacetates has been developed. Upon visible light irradiation, the reaction proceeds smoothly under mild and catalyst-free conditions. A wide scope of 2-pyridones and α-aryldiazoacetates are well tolerated, and various O-alkylated 2-pyridones are obtained with perfect selectivity and good functional group tolerance. A photoinduced radical process is probably responsible for the excellent selectivity.

Copper-Catalyzed Trifluoromethylation of Alkoxypyridine Derivatives

The trifluoromethylation of aromatic and heteroaromatic cores has attracted considerable interest in recent years due to its pharmacological relevance. We studied the extension of a simple copper-catalyzed trifluoromethylation protocol to alkoxy-substituted iodopyridines and their benzologs. The trifluoromethylation proceeded smoothly in all cases, and the desired compounds were isolated and characterized. In the trifluoromethylation of 3-iodo-4-methoxyquinoline, we observed a concomitant O-N methyl migration, resulting in the trifluoromethylated quinolone as a product. Overall, the described procedure should facilitate the broader use of copper-catalyzed trifluoromethylation in medicinal chemistry.

Specific N-Alkylation of Hydroxypyridines Achieved by a Catalyst- and Base-Free Reaction with Organohalides

A specific N-alkylation of 2-hydroxypyridines is achieved by reacting with organohalides under catalyst- and base-free conditions. The observed HX-facilitated conversion of pyridyl ether intermediates to 2-pyridone products may account for the success and specific N-alkylation of the reaction under the unexpectedly simple conditions. This new reaction may provide a useful alternative for the synthesis of 2-pyridones and analogous structures because of its >99% N-selectivity, relatively broad scopes of both substrates, and no mandatory use of catalysts and bases.

Enantioselective propargylic [1,3]-rearrangements: copper-catalyzed O-to-N migrations toward C-N bond formation

We have identified an enantioselective copper-catalyzed O-to-N formal [1,3]-rearrangement to form N-propargylic-2-pyridones. This enantioconvergent O-to-N propargylic rearrangement occurs rapidly at ambient temperature and high enantioselectivity is observed for a range of 3-alkyl-substituted substrates. Stereochemical features include a mild kinetic enantioenrichment of the substrate and a non-linear relationship between product and ligand enantiopurity. Based on kinetic analyses and cross-over experiments, we put forward a mechanistic proposal involving Cu-acetylides as well as bimetallic intermediates in which coordination to the pyridyl nitrogen is likely a crucial binding interaction.

Regioselectivity and Mechanism of Synthesizing N-Substituted 2-Pyridones and 2-Substituted Pyridines via Metal-Free C-O and C-N Bond-Cleaving of Oxazoline[3,2-a]pyridiniums

Novel intermediate oxazoline[3,2-a]pyridiniums were facilely prepared from 2-(2,2-dimethoxyethoxy)-pyridines via acid promoted intramolecular cyclization. Sequentially, the quaternary ammonium salts were treated with different nucleophiles for performing regioselective metal-free C-O and C-N bond-cleaving to afford prevalent heterocyclic structures of N-substituted pyridones and 2-substituted pyridines. The reaction mechanism and regioselectivity were then systematically explored by quantum chemistry calculations at B3LYP/6-31 g(d) level. The calculated free energy barrier of the reactions revealed that aniline and aliphatic amines (e.g., methylamine) prefer to attack C8 of intermediate 4a, affording N-substituted pyridones, while phenylmethanamine, 2-phenylethan-1-amine and 3-phenylpropan-1-amine favor to attack C2 of the intermediate to form 2-substituted pyridines. With the optimized geometries of the transition states, we found that the aromatic ring of the phenyl aliphatic amines may form cation-π interaction with the pyridinium of the intermediates, which could stabilize the transition states and facilitate the formation of 2-substituted pyridines.

Theoretical prediction of the synthesis of 2,3-dihydropyridines through Ir(iii)-catalysed reaction of unsaturated oximes with alkenes

The Ir(iii)-catalysed reaction of unsaturated oximes with alkenes was predicted, and the results indicate a more efficient synthesis of 2,3-dihydropyridines.

A green synthetic approach to synthesizing diverse 2-pyridones for their exceptional UV shielding functions

An efficient catalyst- and solvent-free multicomponent reaction of 4-oxo-4H-chromene-3-carbaldehydes with malonates and ammonium acetate was developed for diverse N-nonsubstituted 2-pyridones.

Iron-catalyzed cross-coupling of unactivated secondary alkyl thio ethers and sulfones with aryl Grignard reagents

The first systematic investigation of unactivated aliphatic sulfur compounds as electrophiles in transition-metal-catalyzed cross-coupling are described. Initial studies focused on discerning the structural and electronic features of the organosulfur substrate that enable the challenging oxidative addition to the C(sp(3))-S bond. Through extensive optimization efforts, an Fe(acac)3-catalyzed cross-coupling of unactivated alkyl aryl thio ethers with aryl Grignard reagents was realized in which a nitrogen "directing group" on the S-aryl moiety of the thio ether served a critical role in facilitating the oxidative addition step. In addition, alkyl phenyl sulfones were found to be effective electrophiles in the Fe(acac)3-catalyzed cross-coupling with aryl Grignard reagents. For the latter class of electrophile, a thorough assessment of the various reaction parameters revealed a dramatic enhancement in reaction efficiency with an excess of TMEDA (8.0 equiv). The optimized reaction protocol was used to evaluate the scope of the method with respect to both the organomagnesium nucleophile and sulfone electrophile.