Light-Driven Intramolecular C-N Cross-Coupling via a Long-Lived Photoactive Photoisomer Complex

Synthesis and Optical Properties of Binaphthyl Derivatives with Comprehensive Introduction of Phenylethynyl Groups

In this study, compounds with phenylethynyl (PE) groups introduced at all of the possible positions of the methylene-bridged structure of the 1,1'-bi-2-naphthol backbone (3-PE to 8-PE) were synthesized. Compounds with four or six phenylethynyl groups (3,6-PE, 4,6-PE, 5,6-PE, 6,7-PE, and 3,4,6-PE) were also synthesized. The key reaction for the synthesis of these compounds was the Sonogashira reaction using halogen scaffolds. The new transformation methods include (1) selective bromination of the 5-position of the binaphthyl skeleton and (2) bromination of the 6-position and then iodination of the 4-position, followed by the Sonogashira reaction of iodine at the 4-position and lithiation and protonation of bromine at the 6-position. The optical properties of the compounds were evaluated. The extension of the π system greatly differed depending on the position of the phenylethynyl group. 4-PE, 4,6-PE, and 3,4,6-PE, in which the phenylethynyl groups were introduced in the extended direction of the naphthalene linkage axis, showed longer absorption and emission wavelengths and higher fluorescence quantum yields than the other compounds. In circularly polarized luminescence measurements, 7-PE showed a relatively large glum value, an interesting finding that reverses the sense.

Visible-light promoted radical cascade cyclization of 3-allyl-2-arylquinazolinones for the synthesis of phosphorylated dihydroisoquinolino[1,2-b]quinazolinones

A novel visible-light promoted metal-free radical cascade cyclization reaction has been developed with 3-allyl-2-arylquinazolinones as a new class of radical acceptor. This photocatalytic protocol represents an efficient approach to construct phosphorylated dihydroisoquinolino[1,2-b]quinazolinones featuring mild conditions, broad substrate scope, and gram-scale synthesis.

Photomediated One-Pot Three-Component Approach Enables the Formal Direct N-Acylation/Sulfonylation and α-C-H Functionalization of 1,2,3,4-Tetrahydroisoquinoline

N-Acyl/sulfonyl-α-functionalized 1,2,3,4-tetrahydroisoquinolines (THIQs) are significant structural motifs in organic synthesis and drug discovery. However, the one-pot approach enabling direct difunctionalization of THIQs remains challenging. Herein we report a photomediated one-pot three-component strategy to access N-acyl/sulfonyl-α-functionalized THIQs. This method features the use of oxygen (from air) as the green oxidant, high atom and step economy, and decent structural diversity. The synthetic applicability of the method was further demonstrated via the facile construction of valuable bioactive molecules. Mechanistic studies indicated that oxidation with singlet oxygen and the acceptor-less dehydrogenation were involved in the photoredox process.

"One pot" synthesis of quinazolinone-[2,3]-fused polycyclic scaffolds in a three-step reaction sequence

Diverse quinazolinone-[2,3]-fused polycyclic skeletons occupy a prominent position in drug discovery. Even with currently available methods there still remain unmet needs for flexible access to such structures. Herein, we have explored a mild "one pot" procedure for the construction of various quinazolinone-[2,3]-fused polycycles. The procedure involves Pd-catalyzed carbonylation of N-(2-iodophenyl)acetamides, release of the masked terminal amine, and two sequential and spontaneous cyclizations. This generally applicable approach features easy assembly of precursors from readily available starting materials, mild reaction conditions, non-cumbersome operation, and polycyclic diversity.

Skeletal Editing of Isatins for Heterocycle Molecular Diversity

Isatins have been widely used in the preparation of a variety of heterocyclic compounds, where the skeletal editing of isatins has shown significant advantages for the construction of diverse heterocycles. This review highlights the progress made in the last decade (2013-2023) in the skeletal editing of the isatin scaffold. A series of ring expansion reactions for the construction of quinoline skeleton, quinolone skeleton, polycyclic quinazoline skeleton, medium-sized ring skeleton, as well as a series of ring opening reactions for the generation of 2-(azoly)aniline skeleton by the cleavage of C-C bond and C-N bond are highlighted. It is hoped that this review will provide some understanding of the chemical transformations of isatins and contribute to the further realization of its molecular diversity.

Visible-Light-Induced Chemodivergent Synthesis of Tetracyclic Quinazolinones and 3-Iminoisoindoliones via the Substrate Control Strategy

A visible-light-induced chemodivergent synthesis of tetracyclic quinazolinones and 3-iminoisoindoliones has been developed. This chemodivergent reaction afforded two kinds of different products by substrate control. A detailed investigation of the reaction mechanism revealed that this consecutive photoinduced electron transfer (ConPET) cascade cyclization involved a radical process, and the aryl radical was the crucial intermediate. This method employed 4-DPAIPN as a photocatalyst and i-Pr2NEt as a sacrificial electron donor leading to metal-free conditions.

Persulfate-Promoted Carbamoylation/Cyclization of Alkenes: Synthesis of Amide-Containing Quinazolinones

The incorporation of amide groups into biologically active molecules has been proven to be an efficient strategy for drug design and discovery. In this study, we present a simple and practical method for the synthesis of amide-containing quinazolin-4(3H)-ones under transition-metal-free conditions. This is achieved through a carbamoyl-radical-triggered cascade cyclization of N3-alkenyl-tethered quinazolinones. Notably, the carbamoyl radical is generated in situ from the oxidative decarboxylative process of oxamic acids in the presence of (NH4)2S2O8.

A Direct Method for Synthesis of Quinoxalines and Quinazolinones Using Epoxides as Alkyl Precursor

An iodine-mediated one-pot synthesis of pyrrolo/indolo [1,2-a]quinoxalines and quinazolin-4-one via utilizing epoxides as alkyl precursors under metal-free conditions has been described. Both 1-(2-aminophenyl)-pyrrole and 2-aminobenzamide could be applied to this protocol. A total of 33 desired products were obtained with moderate to good yields. This methodology was suitable for wide-scale preparation and the obtained products could be further modified into promising pharmaceutically active reagents.

Synthesis of 2,3-Fused Quinazolinones via the Radical Cascade Pathway and Reaction Mechanistic Studies by DFT Calculations

An efficient radical cascade cyclization of unactivated alkenes toward the synthesis of a series of ring-fused quinazolinones has been developed in moderate to excellent yields using commercially available ethers, alkanes, and alcohols, respectively, under a base-free condition in a short time without a transition metal as catalyst. Notably, the transformations can be carried out with the advantages of a broad substrate scope and high atomic economy. Density functional theory calculations and wavefunction analyses were performed to elucidate the radical reaction mechanism.

Synthesis of fused quinazolinones via visible light induced cyclization of 2-aminobenzaldehydes with tetrahydroisoquinolines

This study reports a novel method for the synthesis of fused quinazolinones by visible-light-induced cyclization of 2-aminobenzaldehydes and tetrahydroisoquinolines. The reaction is easily carried out by irradiation with a blue LED in the presence of 9-fluorenone and air. A broad substrate scope with good tolerance of functionalities was observed under the optimized reaction conditions. Moreover, using 2-aminophenone as the substrate and under similar reaction conditions, the same product was obtained when a carbon was removed. The bio-active naturally occurring alkaloid rutaecarpine could be obtained by this strategy. The success of the reaction on the gram-scale and the further transformation of the substrate demonstrated the synthetic practicability of this reaction.

Regioselective synthesis of phenanthridine-fused quinazolinones using a 9-mesityl-10-methylacridinium perchlorate photocatalyst

Herein, we demonstrate a regioselective intramolecular C-N cross-coupling for the synthesis of 14H-quinazolino[3,2-f]phenanthridin-14-one by using 9-mesityl-10-methylacridinium perchlorate as the visible-light (450-470 nm) photocatalyst. The experiments with BHT, TEMPO, and Stern-Volmer quenching studies helped to rationalize a radical pathway via a SET mechanism.

One-Pot Synthesis of Isoxazole-Fused Tricyclic Quinazoline Alkaloid Derivatives via Intramolecular Cycloaddition of Propargyl-Substituted Methyl Azaarenes under Metal-Free Conditions

A practical method was developed for the convenient synthesis of isoxazole-fused tricyclic quinazoline alkaloids. This procedure accesses diverse isoxazole-fused tricyclic quinazoline alkaloids and their derivatives via intramolecular cycloaddition of methyl azaarenes with tert-butyl nitrite (TBN). In this method, TBN acts as the radical initiator and the source of N-O. Moreover, this protocol forms new C-N, C-C, and C-O bonds via sequence nitration and annulation in a one-pot process with broad substrate scope and functionalization of natural products.

A Three-Step Method for the Preparation of N-Substituted 3,4-Dihydroisoquinolin-1(2H)-ones and Heteroaryl-Fused 3,4-Dihydropyridin-2(1H)-ones from 2-Bromobenzoate Precursors

We demonstrate a general method for the preparation of diverse N-substituted 3,4-dihydroisoquinolin-1(2H)-one compounds through an overall three-step cross-coupling/cyclization/N-deprotection/N-alkylation sequence. In the first step, ethyl 2-bromobenzoates and 2-bromo-1-carboxyethyl heterocycles are cross-coupled with commercially available potassium (2-((tert-butoxycarbonyl)amino)ethyl)trifluoroborate to produce (hetero)aryl-substituted 3-[(N-Boc-2-carboxyethyl)phenyl]ethylamines. In a subsequent two-stage process, these (hetero)arylethylamines undergo base-mediated ring closure followed by N-deprotection and N-alkylation to produce N-substituted 3,4-dihydroisoquinolin-1(2H)-ones and heteroaryl-fused N-benzyl 3,4-dihydropyridin-2(1H)-ones. Mechanistic work was performed to elucidate the order of transformations for the latter two-stage process. The method was also extended to the production of N-benzyl isoindolin-1-one and N-benzyl 2,3,4,5-tetrahydro-1H-benzo[c]azepin-1-one.

Synthesis of Quinazolinone-Fused Tetrahydroisoquinolines and Related Polycyclic Scaffolds by Iodine-Mediated sp3 C-H Amination

An iodine-mediated intramolecular sp³ C-H amination reaction producing quinazolinone-fused polycyclic skeletons from 2-aminobenzamide precursors is reported. This reaction does not use transition metals, has a broad substrate scope, and can be used on a gram scale. Under the optimal reaction conditions, a variety of quinazolinone-fused tetrahydroisoquinolines and derivatives of Rutaecarpine were synthesized from readily accessible compounds. The reaction proceeds well with crude 2-aminobenzamide derivatives, allowing for the synthesis of the products from simple 2-aminobenzoic acids and tetrahydroisoquinolines without purification of the 2-aminobenzamide intermediates. Preliminary biological experiments have identified Cereblon (CRBN) inhibitory activity and relevant anti-myeloma medicinal properties in some of these polycyclic products.

Photoinduced α-C-H Amination of Cyclic Amine Scaffolds Enabled by Polar-Radical Relay

Herein, we report a polar-radical relay strategy for α-C-H amination of cyclic amines with N-chloro-N-sodio-carbamates. The relay is initiated by in situ generation of cyclic iminium intermediate using N-iodosuccinimide (NIS) oxidant as an initiator, which then operates through a series of polar (addition and elimination) and radical (homolysis, hydrogen- and halogen atom transfer) reactions to enable the challenging C-N bond formation in a controlled manner. A broad range of α-amino cyclic amines were readily accessed with excellent regioselectivity, and the superb applicability was further demonstrated by functionalization of biologically relevant compounds.

Design, synthesis and bioactivity evaluation of novel N-phenyl-substituted evodiamine derivatives as potent anti-tumor agents

Natural products are important sources for the development of therapeutic medicine, among which evodia fruit has a wide range of medicinal properties in traditional Chinese medicine. Evodiamine, the main active component of evodia fruit, has various anti-cancer effects and has been proved to be a Topo inhibitor. From our previous attempts of modifying evodiamine, we found that the N14 phenyl substituted derivatives had showed great anti-tumor activity, which prompted us to further explore the novel structures and activities of these compounds. Compound 6f, as a N14 3-fluorinated phenyl substituted evodiamine derivative, showed a certain inhibitory activity against Topo I at 200 μM. By studying its anti-tumor effects in vitro, compound 6f could inhibit proliferation and induce apoptosis, as well as arrest the cell cycle of HGC-27 and HT-29 cell lines at G2/M phase in a concentration-dependent manner. Moreover, compound 6f could inhibit the migration and invasion of HGC-27 cell lines. Meanwhile, compound 6f could induce apoptosis of HGC-27 cells by inhibiting PI3K/AKT pathway. Overall, this work demonstrated that the N14 phenyl-substituted evodiamine derivatives had a good inhibitory effect on tumor cells in vitro, providing a promising strategy for developing potential anticancer agents for the treatment of gastrointestinal tumors.

Visible light-driven [3 + 3] annulation reaction of 2H-azirines with Huisgen zwitterions and synthesis of 1,2,4-triazines

A visible light-driven [3 + 3] annulation reaction of 2H-azirines with Huisgen zwitterions is developed for the first time.

Recent Advances on the Synthesis of 2,3-Fused Quinazolinones

As one of the most important structural units in pharmaceuticals and medicinal chemistry, quinazolinone and its derivatives exhibit a wide range of biological and pharmacological activities, including anti-inflammatory, antitubercular, antiviral,...

Redox-neutral access to 3,3′-disubstituted oxindoles via radical coupling reactions

An efficient radical protocol was developed for the assembly of valuable functional oxindoles in the absence of metals, photocatalysts, and bases.

Metal-Free Annulation of 2-Nitrobenzyl Alcohols and Tetrahydroisoquinolines toward the Divergent Synthesis of Quinazolinones and Quinazolinethiones

A simple metal-free method for the synthesis of quinazolinones from commercially available 2-nitrobenzyl alcohols and tetrahydroisoquinolines is developed. The reaction conditions were tolerant of an array of functionalities such as halogen, tertiary amine, protected alcohol, and ester groups. Under nearly identical conditions, quinazolinethiones were obtained in the presence of elemental sulfur and suitable mediators.

Construction of sterically congested oxindole derivatives via visible-light-induced radical-coupling

The oxindole scaffold represents an important structural feature in many natural products and pharmaceutically relevant molecules. Herein, we report a visible-light-induced modular methodology for the synthesis of complex 3,3'-disubstituted oxindole derivatives. A library of valuable fluoroalkyl-containing highly sterically congested oxindole derivatives can be synthesized by a catalytic three-component radical coupling reaction under mild conditions (metal & photocatalyst free, >80 examples). This strategy shows high functional group tolerance and broad substrate compatibility (including a wide variety of terminal or non-terminal alkenes, conjugated dienes and enynes, and a broad array of polyfluoroalkyl iodide and oxindoles), which enables modular modification of complex drug-like compounds in one chemical step. The success of solar-driven transformation, large-scale synthesis, and the late-stage functionalization of bioactive molecules, as well as promising tumor-suppressing biological activities, highlights the potential for practical applications of this strategy. Mechanistic investigations, including a series of control experiments, UV-vis spectroscopy and DFT calculations, suggest that the reaction underwent a sequential two-step radical-coupling process and the photosensitive perfluoroalkyl benzyl iodides are key intermediates in the transformation.

Toolbox for Distal C-H Bond Functionalizations in Organic Molecules

Transition metal catalyzed C-H activation has developed a contemporary approach to the omnipresent area of retrosynthetic disconnection. Scientific researchers have been tempted to take the help of this methodology to plan their synthetic discourses. This paradigm shift has helped in the development of industrial units as well, making the synthesis of natural products and pharmaceutical drugs step-economical. In the vast zone of C-H bond activation, the functionalization of proximal C-H bonds has gained utmost popularity. Unlike the activation of proximal C-H bonds, the distal C-H functionalization is more strenuous and requires distinctly specialized techniques. In this review, we have compiled various methods adopted to functionalize distal C-H bonds, mechanistic insights within each of these procedures, and the scope of the methodology. With this review, we give a complete overview of the expeditious progress the distal C-H activation has made in the field of synthetic organic chemistry while also highlighting its pitfalls, thus leaving the field open for further synthetic modifications.

Design, synthesis and bioactivity study of evodiamine derivatives as multifunctional agents for the treatment of hepatocellular carcinoma

Topoisomerase has been found extremely high level of expression in hepatocellular carcinoma (HCC) and proven to promote the proliferation and survival of HCC. Cancer-associated fibroblasts (CAFs) as a kind of key reactive stromal cell that abundantly present in the microenvironment of HCC, could enhance the metastatic ability and drug resistance of HCC. Therefore, developing new drugs that address the above conundrums would be of the upmost significant in the fight against HCC. Evodiamine, as a multi-target natural product, has been found to exert various biological activities such as anti-cancer and anti-hepatic fibrosis via blocking topoisomerase, NF-κB, TGF-β/HGF, and Smad2/3. Inspired by these facts, 15 evodiamine derivatives were designed and synthesized for HCC treatment by simultaneously targeting Topo I and CAFs. Most of them displayed preferable anti-HCC activities on three HCC cell lines and low cytotoxicity on one normal hepatic cell. In particular, compound 8 showed the best inhibitory effect on HCC cell lines and a good inhibition on Topo I in vitro. Meanwhile, it also induced obvious G₂/M arrest and apoptosis, and significantly decreased the migration and invasion capacity of HCC cells. In addition, compound 8 down-regulated the expression of type I collagen in the activated HSC-T6 cells, and induced the apoptosis of activated HSC-T6 cells. In vivo studies demonstrated that compound 8 markedly decreased the volume and weight of tumor (TGI = 40.53%). In vitro and in vivo studies showed that its effects were superior to those of evodiamine. This preliminary attempt may provide a promising strategy for developing anti-HCC lead compounds taking effect through simultaneous inhibition on Topo I and CAFs.

Photoinduced homolytic decarboxylative acylation/cyclization of unactivated alkenes with α-keto acid under external oxidant and photocatalyst free conditions: access to quinazolinone derivatives

A novel and green strategy for the synthesis of acylated quinazolinone derivatives via photo-induced decarboxylative cascade radical acylation/cyclization of quinazolinone bearing unactivated alkenes has been developed. The protocol provides a novel route to access acyl radicals from α-keto acids through a self-catalyzed energy transfer process. Most importantly, the reaction proceeded smoothly without any external photocatalyst, additive or oxidant, and could be easily scaled-up in flow conditions with sunlight irradiation.

Visible-Light-Mediated Synthesis of Rutaecarpine Alkaloids through C–N Cross-Coupling Reaction

A visible-light-initiated cross-dehydrogenative-coupling amination is described, featuring metal- and photocatalyst-free, at room temperature, and using air as an oxidant. The reaction provides a facile approach for the synthesis of rutaecarpine and its derivatives. The substrates with electron-withdrawing groups give higher yields than those with electron-donating groups, but the substituent position has a negligible influence on the yield. Using binaphthyl-diyl hydrogen phosphate and dibenzyl phosphate as catalysts both deliver satisfying yields. This straightforward light-driven strategy might be applicable to the synthesis of quinazolinone derivatives.

Ru(ii)-Catalyzed C-H addition and oxidative cyclization of 2-aryl quinazolinones with activated aldehydes

The ruthenium(ii)-catalyzed cross-coupling reaction between 2-aryl quinazolinones and activated aldehydes is described. This method enables the site-selective hydroxyalkylation under redox-neutral conditions. Moreover, this protocol provides a facile access to various tetracyclic isoindoloquinazolinones by using Cu(OAc)₂ as an external oxidant via C-H addition and subsequent intramolecular cyclization. A wide substrate scope and a high level of chemoselectivity as well as broad functional group tolerance are observed.

Electrosynthesis of polycyclic quinazolinones and rutaecarpine from isatoic anhydrides and cyclic amines

A direct decarboxylative cyclization between readily available isatoic anhydrides and cyclic amines was established to construct polycyclic fused quinazolinones employing electrochemical methods. This procedure was performed in an undivided cell without the use of a transition-metal-catalyst and external oxidant. A broad scope of polycyclic fused quinazolinones were obtained in moderate to good yields. Additionally, rutaecarpine was also prepared through our method in one step in good yield.

Polycyclic quinazolinones and rutaecarpine were synthesized from isatoic anhydrides and cyclic amines through an electrochemical method without an external oxidant and transition-metal-catalyst.

Transition metal-catalyzed sp3 C-H activation and intramolecular C-N coupling to construct nitrogen heterocyclic scaffolds

Nitrogen heterocycles are of great medicinal importance, and the construction of nitrogen heterocyclic scaffolds has been one of the focuses in synthetic organic chemistry. Recently, the strategy of transition metal-catalyzed sp3 C-H activation and intramolecular C-N coupling to construct nitrogen heterocyclic scaffolds has been well developed. Palladium, copper, silver, nickel, cobalt, ruthenium and rhodium catalysis were successfully used for the construction of nitrogen heterocyclic scaffolds, aziridines, azetidines, pyrrolidines, pyrrolidine-2,5-diones, indolines, isoindolines, isoindolinones, tetrahydropyridines, oxazolidinones, oxazinanones, β-lactams, γ-lactams etc., which have been synthesized by the sp3 C-H activation strategy. Here, we summarize the progress of transition metal-catalyzed sp3 C-H activation/intramolecular C-N bond formation, and introduce both the reaction development and mechanisms in numerous synthetically useful intramolecular sp3 C-H catalytic aminations/amidations.

Photo- and dioxygen-enabled radical C(sp3)–N(sp2) cross-coupling between guanidines and perfluoroalkyl iodides

The utilization of visible light and dioxygen (air) as green and sustainable mediators in photocatalyzed synthetic chemistry is demonstrated.