Practical Synthesis of 3-Aryl Anthranils via an Electrophilic Aromatic Substitution Strategy

Nitrogen-Based Organofluorine Functional Molecules: Synthesis and Applications

Fluorine and nitrogen form a successful partnership in organic synthesis, medicinal chemistry, and material sciences. Although fluorine-nitrogen chemistry has a long and rich history, this field has received increasing interest and made remarkable progress over the past two decades, driven by recent advancements in transition metal and organocatalysis and photochemistry. This review, emphasizing contributions from 2015 to 2023, aims to update the state of the art of the synthesis and applications of nitrogen-based organofluorine functional molecules in organic synthesis and medicinal chemistry. In dedicated sections, we first focus on fluorine-containing reagents organized according to the type of fluorine-containing groups attached to nitrogen, including N-F, N-RF, N-SRF, and N-ORF. This review also covers nitrogen-linked fluorine-containing building blocks, catalysts, pharmaceuticals, and agrochemicals, underlining these components' broad applicability and growing importance in modern chemistry.

Fusion of Four Aromatic Rings via an Atom-Mutual-Embedding Strategy to Form a Tetrahexacyclic System

Skeletal manipulation of aromatic compounds has emerged as a potent tool in synthetic chemistry, but simultaneous multiring manipulation remains largely unexplored due to the inherent complexities of ring and site selectivity. Herein, we report an unprecedented multiring skeletal manipulation that fuses four 5-membered aromatic rings, comprising two organic and two metal-containing aromatic systems, into a novel metal-bridged 6/6/6/6-membered ring scaffold. The sequential ring fusion is accomplished through an atom-mutual-embedding strategy; this strategy entails the stepwise insertion of two nitrogen atoms into separate metal-carbon bonds and simultaneously integrates a metal atom as a bridge across two isoxazole moieties. The presence of a central metal atom is crucial for ensuring precise substrate alignment and enhancing both the ring and site specificity. The resulting tetrahexacyclic products exhibit remarkable stability and superior near-infrared (NIR) functional properties, surpassing those of the precursor compounds. This work not only establishes a conceptual foundation for designing versatile substrate molecules amenable to intricate editing but also contributes to the rational and performance-targeted manipulation of molecular architectures.

Triflic Acid-Mediated Chemoselective Indole C2-Heteroarylation of Peptide Tryptophan Residues by Triazine

Peptide modification provides opportunities to afford peptides with designed functions. Among the proteogenic amino acids, tryptophan represents an ideal and attractive target for peptide modification because of the exclusive chemical reactivity of its unique indole structure. Herein, we reported an indole C2 position-selective and transition-metal-free modification approach for indole derivatives and tryptophan-containing peptides by triazine derivatives via triflic acid activation and that the incorporated functional group could act as an orthogonal handle for further bioconjugation via an inverse electron demand Diels-Alder reaction.

Tf2O-mediated [4+2]-annulation of anthranils with 2-chloropyridines: enabling access to pyridoquinazolinones and euxylophoricine B

We present an efficient approach for synthesizing pyridoquinazolinones in the presence of triflic anhydride utilizing anthranils and 2-chloropyridines as starting materials. In this process, Tf2O initially activates anthranils forming an electrophilic 1-((trifluoromethyl)sulfonyl)benzo[c]isoxazol-1-ium species. This species undergoes an in situ annulation reaction with 2-chloropyridines, resulting in therapeutically useful pyridoquinazolinones. The reaction is tolerant to various functional groups, allowing access to a wide range of substituted pyridoquinazolinones in good yields. Furthermore, the synthesis of euxylophoricine B, known to be an antitumor agent, was also achieved.

Ag-Catalyzed Practical Synthesis of N-Acyl Anthranilic Acids from Anthranils and Carboxylic Acids

A practical synthesis of valuable N-acyl anthranilic acids has been achieved via a silver-catalyzed imino-ketene generation from readily available anthranils and carboxylic acids. A wide range of carboxylic acids including sterically demanding aliphatic carboxylic acids, aromatic carboxylic acids, acrylic acids, and amino acids are compatible in this reaction. Moreover, this method can be used to modify drug molecules and natural products, such as ibuprofen, probenecid, and acetylglycine.

Synthesis of 4-styrylquinolines via direct oxidative C3-alkenylation of anthranils under Pd(II) catalysis

The palladium-catalyzed oxidative C3-alkenylation of anthranils (2,1-benzisoxazoles) with various styrenes has been successfully achieved. The C3-alkenylated anthranils were subsequently utilized in a [4+2]-cycloaddition with in situ generated α,β-unsaturated ketones leading to the synthesis of a diverse range of olefin-containing quinolines. Notably, this reaction exclusively yielded mono-alkenylated products with E-selectivity. The optimized catalytic conditions were compatible with a wide variety of substituted olefins and anthranils, forming various C3-alkenylated anthranils with good yields. To showcase the application of the present methodology, the C3-alkenylated anthranils have been employed as synthons to access a wide range of substituted quinolines.

Tf2O-Promoted Chemoselective C3 Functionalization of Anthranils with Phenols and Thiophenols

Different chemoselectivities of phenols and thiophenols were observed in a Tf₂O-promoted C3 functionalization of simple anthranils. The reaction of phenols and anthranils gives 3-aryl anthranils via a C-C bond formation, whereas thiophenols afford 3-thio anthranils through a C-S bond formation. Both reactions have a broad substrate scope and tolerate a wide range of functional groups, affording the corresponding products with specific chemoselectivity.

NiH-Catalyzed Proximal-Selective Hydroamination of Unactivated Alkenes with Anthranils

The regioselective hydroamination of unactivated alkenes is a long-standing challenge in organic synthesis. Herein, we report a NiH-catalyzed proximal-selective hydroamination of unactivated alkenes with 8-aminoquinoline (AQ) as a bidentate auxiliary and anthranils as aminating reagents. A wide range of primary aryl amines bearing an ortho-carbonyl group were installed in both terminal and internal unactivated alkenes, delivering a variety of valuable β- and γ-amino acid building blocks, respectively, with excellent regiocontrol. The utility of this transformation was further demonstrated by the conversion of the multifunctionalized aryl amines into useful N-heterocycles.

Electrochemical Site-Selective Alkylation of Azobenzenes with (Thio)Xanthenes

Herein, we first report an electrochemical methodology for the site-selective alkylation of azobenzenes with (thio)xanthenes in the absence of any transition metal catalyst or external oxidant. A variety of groups are compatible with this electrochemical alkylation, which furnishes the products in moderate to good yields.