Selective Oxidative Decarbonylative Cleavage of Unstrained C(sp(3))-C(sp(2)) Bond: Synthesis of Substituted Benzoxazinones

Recent Progress in the Synthesis of Benzoxazin-4-Ones, Applications in N-Directed Ortho-Functionalizations, and Biological Significance

The development of efficient synthetic procedures to access fused N, O-heterocyclic skeletons has been a pivotal research topic in organic synthesis for several years. Owing to the applications of N, O-fused heterocycles in organic synthesis, material sciences, and medicinal chemistry, significant efforts have been dedicated to design novel methods for their construction. To this end, 1,3-benzoxazin-4-ones are privileged candidates for N, O-heterocyclic molecules often found in natural products, agrochemicals, and materials science applications. In this review, we aim to summarize the existing literature on the synthesis of 1,3-benzoxazin-4-ones from 2010 onwards. Moreover, 1,3-benzoxazin-4-ones have also been identified as an excellent native directing group for the ortho-functionalization via C-H activation, which is often a strenuous task requiring pre-functionalized substrates. In the latter part of this report, we compiled several interesting examples of N-directed functionalizations of 1,3-benzoxazin-4-ones. Additionally, to emphasize biological importance, recent developments on the anticancer evaluations of benzoxazine-4-one core are included. We believe that by harnessing the methodologies discussed herein, new possibilities could be unlocked for the synthesis of fused N, O-heterocycles, leading to the development of novel biologically active compounds and functional materials.

De(sulfon)amidative Cyclization: The Synthesis of Dibenzolactams and Dibenzosultams for Organic Light Emitting Diode Materials

This study addresses a challenge in organic synthetic chemistry: the direct cleavage of amide bonds, which is typically hampered by the thermodynamic stability of the C(Ar)-C(acyl) bond. Previous methods often rely on "CO" extrusion-jointing transition metal-catalyzed process and require activated tertiary amides, limiting their applicability due to incompatibility with reactive functional groups such as halogens. Herein, we report a transition metal-free approach for the deamidative cyclization of biaryl diamides via a radical process, yielding dibenzolactam derivatives. Along this line, we have developed the desulfonamidative cyclization of biaryl disulfonamides to produce dibenzosultams through direct nucleophilic aromatic substitution, demonstrating high selectivity for unsymmetrical structures. Additionally, unsymmetrical sulfamoyl biaryl amides, containing both amide and sulfonamide functionalities, can selectively undergo desulfonamidative coupling with the amide to form dibenzolactams, which offers a complementary synthetic pathway to unsymmetric dibenzolactams. These protocols exhibit excellent compatibility with reactive functional groups, including halogens, providing an innovative synthetic toolbox for the development of thermally activated delayed fluorescence (TADF) materials used in organic light emitting diodes (OLEDs). DMAC-PDO, incorporating a dibenzolactam as the acceptor unit, serves as an efficient blue TADF emitter with a maximum external quantum efficiency (EQEmax) of 23.4 %.

Aniline assisted dimerization of phenylalanines: convenient synthesis of 2-aroyl-3-arylquinoline in an I2-DMSO system

We herein report an efficient synthesis of 2-aroyl-3-arylquinolines from phenylalanines and anilines. The mechanism involves I₂-mediated Strecker degradation enabled catabolism and reconstruction of amino acids and a cascade aniline-assisted annulation. Both DMSO and water act as oxygen sources in this convenient protocol.

Rhodium-Catalyzed Azine-Directed C-H Amidation with N-Methoxyamides

Using N-methoxyamide reagents as an amide source, C-H amidation was realized at the ortho position of azine under the action of rhodium and boric acid. The method has mild reaction conditions, high atomic utilization, excellent yield, and wide adaptability to amidation reagents (both aromatic amides and fatty amides are applicable). Amide-substituted ketones can be obtained by a simple treatment and can be further transformed into bioactive substances. This provides a good supplement for the C-H bond amidation of aromatic rings.

Pd-Catalyzed Carbonylative Synthesis of 4H-Benzo[d][1,3]Oxazin-4-Ones Using Benzene-1,3,5-Triyl Triformate as the CO Source

A facile synthesis of 4H-benzo[d][1,3]oxazin-4-one derivatives by Pd-catalyzed carbonylative cross-coupling between N-(ortho-bromoaryl)amides and benzene-1,3,5-triyl triformate (TFBen) was developed. This procedure does not require the toxic and flammable gas CO as the carbonyl source and tolerates a wide scope of functional groups. Remarkably, 4H-benzo[d][1,3]oxazin-4-ones incorporated to natural products and drugs can be constructed by this method.

Recent advances in decarbonylative annulation reactions

In recent years, decarbonylative annulation reactions have emerged as one of the most efficient routes to construct a variety of important carbocyclic and heterocyclic scaffolds. The main advantages of this type of reaction are, first, the carbonyl compounds are used as the starting materials which are abundant in nature and second, the major by-product of this reaction is carbon monoxide. In the last two decades, various intramolecular and intermolecular decarbonylative annulation reactions have been performed using carbonyl compounds and alkenes/alkynes/arenes/isocyanates etc. as the annulation partners. These reactions are typically performed either in the presence of or in the absence of a metal catalyst. However, these reactions are still in their infancy as a very little progress has been achieved in these reactions. Through this review article, it is attempted to highlight the recent developments on various decarbonylative annulation reactions which ultimately lead to the formation of important structural moieties.

Iodine Catalyzed Oxidative Coupling of Diaminoazines and Amines for the Synthesis of 3,5-Disubstituted-1,2,4-Triazoles

A simple, convenient, transition metal-free one pot synthesis of 3,5-disubstituted-1,2,4-triazoles has been established. The innovation in this reaction is the use of easily available 1,1-diaminoazines as substrates. This method provides the products with wider substrate scope, at an expedited rate, and with relatively better yields in comparison to the reported methods. The reaction mechanism involves an initial intermolecular nucleophilic addition (facilitated by I₂) followed by intramolecular nucleophilic cyclization.

C-C Bond Cleavage Initiated Cascade Reaction of β-Enaminones: One-Pot Synthesis of 5-Hydroxy-1H-pyrrol-2(5H)-ones

An unprecedented C(CO)-C(Ar) bond cleavage of β-enaminones has been realized under mild and transition-metal-free conditions. The cascade transformation based on this C-C bond cleavage involves 1,3-O/C migration and aerobic hydroxylation and leads to various 5-hydroxy-1H-pyrrol-2(5H)-ones with broad functional group tolerance. The application of this methodology has been showcased by preparing 5-alkoxy-1H-pyrrol-2(5H)-one derivatives and a pyrrolo[2,1-a]isoquinolin-3-one derivative.

Transition-metal-free decarbonylative alkylation towards N-aryl α-hydroxy amides via triple C–C bond cleavages and their selective deuteration

A transition-metal-free decarbonylative alkylation reaction for the synthesis of N-aryl α-hydroxy amides via precise cleavages and reorganizations of three C–C σ bonds has been developed.

Photoactivatable prodrug for simultaneous release of mertansine and CO along with a BODIPY derivative as a luminescent marker in mitochondria: a proof of concept for NIR image-guided cancer therapy

Controlled and efficient activation is the crucial aspect of designing an effective prodrug. Herein we demonstrate a proof of concept for a light activatable prodrug with desired organelle specificity. Mertansine, a benzoansamacrolide, is an efficient microtubule-targeting compound that binds at or near the vinblastine-binding site in the mitochondrial region to induce mitotic arrest and cell death through apoptosis. Despite its efficacy even in the nanomolar level, this has failed in stage 2 of human clinical trials owing to the lack of drug specificity and the deleterious systemic toxicity. To get around this problem, a recent trend is to develop an antibody-conjugatable maytansinoid with improved tumor/organelle-specificity and lesser systematic toxicity. Endogenous CO is recognized as a regulator of cellular function and for its obligatory role in cell apoptosis. CO blocks the proliferation of cancer cells and effector T cells, and the primary target is reported to be the mitochondria. We report herein a new mitochondria-specific prodrug conjugate (Pro-DC) that undergoes a photocleavage reaction on irradiation with a 400 nm source (1.0 mW cm⁻²) to induce a simultaneous release of the therapeutic components mertansine and CO along with a BODIPY derivative (BODIPY(PPH₃)₂) as a luminescent marker in the mitochondrial matrix. The efficacy of the process is demonstrated using MCF-7 cells and could effectively be visualized by probing the intracellular luminescence of BODIPY(PPH₃)₂. This provides a proof-of-concept for designing a prodrug for image-guided combination therapy for mainstream treatment of cancer.

Simultaneous release of two therapeutic reagents, mertansine and CO through photo-induced cleavage of a mitochondria-specific prodrug with improved drug efficacy.

Synthesis, In Vitro Anticancer Activity and In Silico Study of some Benzylidene Hydrazide Derivatives

Some benzylidenehydrazides (3a-e) have been synthesized in three reaction steps from anthranilic acid in good yields, about 70% - 99%. The structures of the synthesized compounds were analyzed using spectroscopic methods. The compounds were evaluated its activity against human lung cancer, A549 cell line by MTT method and studied its molecular docking onto the protein tyrosine kinase (PDB ID: 1M17) by using Molegro® vs. 5.5. The data showed that N-(2-(2-(4-nitrobenzylidene)hydrazinecarbonyl)phenyl)benzamide (3d) which synthesized in 70% yield and has the highest activity on inhibiting the growth of A549 cell line with IC50 10.9μg/mL, which was linier with our in silico study. Compound 3d has the smallest RS value -94.44 kcal/mol, lower than selected Ligand, Erlotinib.

Divergent Conversion of N-Acyl-isoxazol-5(2 H)-ones to Oxazoles and 1,3-Oxazin-6-ones Using Photoredox Catalysis

The fragmentation of N-acyl-isoxazol-5-ones using visible light photoredox catalysis has been disclosed. The catalyst-controlled divergent mechanisms, namely the oxidative and reductive quenching catalytic cycle, are utilized. Various oxazoles and 1,3-oxazin-6-ones are selectively obtained from the same isoxazol-5-one skeleton under mild conditions.

Cleavage of carbon–carbon bonds by radical reactions

This review provides insights into the in situ generated radicals triggered carbon–carbon bond cleavage reactions.

A carbene-catalyzed tandem isomerization/cyclisation strategy: an efficient assembly of benzoxazinones

An unprecedented example of NHC-catalyzed tandem isomerization/cyclisation is reported to synthesize benzoxazinones.

Cobalt(iii)-catalyzed C–H amidation of weakly coordinating sulfoxonium ylides and α-benzoylketene dithioacetals

Cobalt(iii)-catalyzed mild C–H amidation of weakly coordinating sulfoxonium ylides and α-benzoylketene dithioacetals has been realized.

I2/DMSO-mediated multicomponent reaction of o-hydroxyaryl methyl ketones, rongalite, and DMSO: access to C3-sulfenylated chromones

An efficient I₂–DMSO reagent system-mediated multicomponent reaction strategy for the synthesis of C3-sulfenylated chromones from o-hydroxyaryl methyl ketones, rongalite, and dimethyl sulfoxide has been developed.

Base-promoted amide synthesis from aliphatic amines and ynones as acylation agents through C-C bond cleavage

A new protocol for the synthesis of amides via base-promoted cleavage of the C(sp)-C(CO) bond of ynones with aliphatic primary and secondary amines under transition-metal-, ligand-, and oxidant-free conditions has been developed. This method exhibits a wide substrate scope, high functional group tolerance and exclusive chemoselectivity, as well as mild reaction conditions.

Base-promoted [3 + 3] cyclization of cyclopropenones and cyclopropenethiones with amides for the synthesis of 6H-1,3-oxazin-6-ones and 6H-1,3-thiazin-6-ones

A facile synthesis of 6H-1,3-oxazin-6-ones and 6H-1,3-thiazin-6-ones has been achieved in the base-promoted [3 + 3] cyclization of cyclopropenones and cyclopropenethiones with amides.

Synthesis of polysubstituted pyridines from oxime acetates using NH4I as a dual-function promoter

An NH₄I dual-function promoter enables pyridine synthesis through oxime N–O bond reduction and subsequent condensation reactions.

Iodine-catalyzed synthesis of N,N′-diaryl-o-phenylenediamines from cyclohexanones and anilines using DMSO and O2 as oxidants

An I₂/DMSO system has been successfully applied to synthesize N,N′-diaryl-o-phenylenediamines from cyclohexanones for the first time.

Iodine/DMSO oxidations: a contemporary paradigm in C–N bond chemistry

A new era in the organic synthetic world is demanding greener protocols for the execution of reactions.

Base-promoted C–C bond cleavage for the synthesis of 2,3,4-trisubstituted pyrroles from N-propargyl β-enaminones

The synthesis of 2,3,4-trisubstituted pyrroles via base-promoted C–C bond cleavage reaction of N-propargyl β-enaminones is reported.

Rhodium(iii)-catalysed decarbonylative annulation through C–H activation: expedient access to aminoisocoumarins by weak coordination

Rh-Catalysed decarbonylative annulation of isatoic anhydrides with alkynes through C–H activation for the direct synthesis of 8-aminoisocoumarins has been developed.

2-Substituted Aniline as a Simple Scaffold for LuxR-Regulated QS Modulation

The ability of the 2-substituted aniline motif to serve as a scaffold for designing potential LuxR-regulated quorum sensing (QS) modulators has been investigated, using docking experiments and biological evaluation of a series of 15 specially synthesized compounds. Aniline, 2-acetyl-aniline and 2-nitroaniline were considered, as well as their N-acylated derivatives. Docking experiments showed that the 2-substituted aniline motif fits within the LuxR binding site at the place of the lactone moiety of AHL, and the biological evaluation revealed QS antagonisitic activity for several compounds, validating the hypothesis that this scaffold acts on QS. Structure activity relationships are discussed regarding interactions with the key residues of the LuxR binding site, showing significant variations in the H-bonding pattern.

Palladium-Catalyzed Removable 8-Aminoquinoline Assisted Chemo- and Regioselective Oxidative sp2-C-H/sp3-C-H Cross-Coupling of Ferrocene with Toluene Derivatives

The coupling of the C(sp²)-H bond of ferrocene with toluene avoiding in situ functionalization of both coupling partners has been achieved using palladium and iron dual catalysis. This cross oxidative coupling features regioselectivity to primary and secondary C(sp³)-H bonds and chemoselectivity toward the -C(sp³)-H over C-I bond of toluene with gram-scale production. It seems Fe(II) catalyst not only stabilizes the generated benzyl radical but also tames its oxidizing behavior, and consequently transfers it to the palladacycle for C-C coupling.

Visible-light-induced oxidant and metal-free dehydrogenative cascade trifluoromethylation and oxidation of 1,6-enynes with water

Generally, oxy-trifluoromethylation in olefins is achieved using oxidants and transition metal catalysts. However, labile olefins remain unexplored due to their incompatibility with harsh reaction conditions. Here, unprecedented light-induced oxidant and metal-free tandem radical cyclization-trifluoromethylation and dehydrogenative oxygenation of 1,6-enynes have been achieved using a photoredox catalyst, CF3SO2Na, and phenanthrene-9,10-dione (PQ), Langlois' reagent (CF3SO2Na) and water as the oxygen source. This benign protocol allows for access to various CF3-containing C3-aryloyl/acylated benzofurans, benzothiophenes, and indoles. Moreover, the oxidized undesired products, which are inherently formed by the cleavage of the vinylic carbon and heteroatom bond, have been circumvented under oxidant free conditions. The mechanistic investigations by UV-visible and ESR spectroscopy, electrochemical studies, isotope labelling and density functional theory (DFT) suggest that light induced PQ produced a CF3 radical from CF3SO2Na. The generated CF3 radical adds to the alkene, followed by cyclization, to provide a vinylic radical that transfers an electron to PQ and generates a vinylic cation. Alternatively, electron transfer may occur from the CF3-added alkene moiety, forming a carbocation, which would undergo cationic cyclization to generate a vinylic carbocation. The subsequent addition of water to the vinylic cation, followed by the elimination of hydrogen gas, led to the formation of trifluoromethylated C3-aryloyl/acylated heterocycles.

Ag(i)-Catalyzed cycloisomerization reactions: synthesis of substituted phenanthrenes and naphthothiophenes

Ag-Catalyzed synthesis of substituted phenanthrenes and naphthothiophenes from ortho-alkylated biaryl derivatives via 6-endo-dig intramolecular alkyne–arene coupling has been described.

1,2-Arylalkylation of N-(arylsulfonyl)acrylamides using aliphatic aldehydes as the alkyl source

A metal-free decarbonylative arylalkylation of N-(arylsulfonyl)acrylamides using aliphatic aldehydes as the alkyl radical source was developed.

Copper-catalyzed transformation of ketones to amides via C(CO)–C(alkyl) bond cleavage directed by picolinamide

Copper catalyzed chemoselective cleavage of the C(CO)–C(alkyl) bond leading to C–N bond formation with chelation assistance of N-containing directing groups is described.