Synthesis of Tetracyclic Quinazolinones Using a Visible-Light-Promoted Radical Cascade Approach

Mn-Catalyzed Electrooxidative Radical Cascade Cyclization for the Synthesis of 6-Phosphorylated Quinoxalino[2,1-b]quinazolin-12-ones

Due to their important potential medicinal value, chemists are pursuing mild and efficient methods to synthesize structurally diverse quinazolinone derivatives. In this paper, a series of isocyano-tethered N-aryl quinazolinones were designed and synthesized to conduct electrocatalytic radical cascade cyclization reactions with phosphine oxides by utilizing inexpensive MnII salt as the catalyst. The desired 6-phosphorylated quinoxalino[2,1-b]quinazolin-12-ones were obtained in moderate to good yields.

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.

Oxidative cascade cyclization of N-arylacrylamides with TMSN3

An azido-radical-triggered cyclization of N-(o-cyanobiaryl)acrylamides with TMSN3via a C(sp3)-N/C(sp2)-C(sp3)/C(sp2)-N bond formation cascade is described. This reaction features mild conditions and high bond-forming efficiency, making it an efficient method for the construction of azide-substituted pyridophenanthridines.

Visible-Light-Promoted Cascade Cyclization of 3-Ethynyl-[1,1'-biphenyl]-2-Carbonitriles with Unsaturated α-Bromocarbonyls

A visible-light-promoted cascade cyclization of 3-ethynyl-[1,1'-biphenyl]-2-carbonitriles with unsaturated α-bromocarbonyls for the synthesis of tetrahydrobenzo[mn]cyclopenta[b]acridines is described. Three C(sp3)-C(sp2) bonds, one C(sp2)-N bond, and three cycles can be formed in a single reaction through the addition of a C-centered radical to the carbon-carbon triple bond and three radical cyclizations. This reaction features mild conditions, wide substrate scope, and high bond-forming efficiency.

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.

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.

The Renaissance of Organo Nitriles in Organic Synthesis

In the arena of functional group-oriented organic synthesis, the nitrile or cyano functionality is of immense importance. The presence of nucleophilic N -atom, π-coordinating ability of the triple bond, and electrophilic C-center imparts unique and interesting reactivity. Owing to the ability of the nitrile to transform into various other functional groups or intermediates, the chemistry is very rich and diverse. In particular, the involvement of nitrile in numerous organic reactions such as inter- or intramolecular alkyne insertion, [2 + 2 + 2] cycloaddition with alkynes, [3 + 2] cycloaddition with azides, [4 + 2] cycloaddition with diene allow the synthesis of many important carbocycles and heterocycles. Furthermore, the nitrile serves as a directing group in many C-H bond functionalization reactions to introduce diverse functionality and participate as a radical acceptor in radical cascade strategies to obtain a large variety of functional molecules. This review mainly focuses on the reactivity and diverse synthetic application of the nitrile including C-H bond functionalization, alkyne insertion, cycloaddition, and thermal or photochemical cascade strategy. The objective of the current review aims at bringing out the striking collection of various nitrile-triggered organic transformations.

Rapid Synthesis of Luotonin A Derivatives via Synergistic Visible-Light Photoredox and Acid Catalysis

The merging of visible-light photoredox and acid catalysis allowed for an intramolecular Povarov cycloaddition reaction using eosin Y as the photocatalyst and TsOH·H₂O as the co-catalyst. A visible-light-promoted dehydrogenative cyclization protocol enabled the construction of Luotonin A derivatives with up to 97% yield.

A Photosensitizer-Free Radical Cascade for Synthesizing CF3-Containing Polycyclic Quinazolinones with Visible Light

Herein, we report an efficient photoinduced radical tandem trifluoromethylation/cyclization reaction of N-cyanamide alkenes for the synthesis of functionalized quinazolinones. Importantly, the reaction is carried out under mild conditions without any additional photosensitizer, metal, or extra additives. A series of trifluoromethyl quinazolinones were prepared efficiently with good yields and excellent functional group tolerance. Preliminary mechanistic experiments were conducted to indicate that the transformation proceeds via a possible mechanism involving photoexcited EDA complex and chain propagation.

Copper-Catalyzed Difluoroalkylation of Alkene/Nitrile Insertion/Cyclization Tandem Sequences: Construction of Difluorinated Bicyclic Amidines

A copper-catalyzed difluoroalkylation of an alkene/nitrile insertion/cyclization tandem sequence of N-cyanamide alkene was described, which provided a convenient synthetic approach for accessing difluorinated bicyclic amidines bearing imine moieties in a sustainable fashion. This protocol is characterized by high yields, a broad substrate scope, and good functional group compatibility. In addition, the desired product can be readily converted into other valuable functionalized fluorinated aza-heterocycles.

Nitriles as radical acceptors in radical cascade reactions

The application of the cyano group as a radical acceptor in the cascade reactions for the construction of various important heterocycles and carbocycles was summarized.

Palladium-catalyzed cascade reactions in aqueous media: synthesis and photophysical properties of pyrazino-fused quinazolinones

A convenient, efficient, and direct approach toward the synthesis of pyrazino-fused quinazolinone frames has been developed. The photophysical properties of 3e with the AIE effect were investigated.

Access to Cyanoimines Enabled by Dual Photoredox/Copper-Catalyzed Cyanation of O-Acyl Oximes

An efficient strategy for the synthesis of pharmaceutically important and synthetically useful cyanoimines, as well as cyanamides, has been described. This strategy is enabled by dual photoredox/copper-catalyzed cyanation of O-acyl oximes or O-acyl hydroxamides. This state of the art protocol for cyanoimines and cyanamides features readily available starting materials, mild reaction conditions, good functional group tolerance, and operational simplicity. The resultant cyanoimines can be transformed into structurally diverse and functionally important N-containing heterocycles.

Nanocrystalline ZnO: A Competent and Reusable Catalyst for the Preparation of Pharmacology Relevant Heterocycles in the Aqueous Medium

:

Nanoparticle catalyzed synthesis is a green and convenient method to achieve most of the chemical transformations in water or other green solvents. Nanoparticle ensures an easy isolation process of catalyst as well as products from the reaction mixture avoiding the hectic work up procedure. Zinc oxide is a biocompatible, environmentally benign and economically viable nanocatalyst with effectivity comparable to the other metal nanocatalyst employed in several reaction strategies. This review mainly focuses on the recent applications of zinc oxide in the synthesis of biologically important heterocyclic molecules under sustainable reaction conditions.

:

Application of zinc oxide in organic synthesis: Considering the achievable advantages of this nanocatalyst, presently several research groups are paying attention in anchoring zincoxide or its modified structure in several types of organic conversions e.g. multicomponent reactions, ligand-free coupling reactions, cycloaddition reaction, etc. The advantages and limitations of this nanocatalyst are also demonstrated. The present study aims to highlight the recent multifaceted applications of ZnO towards the synthesis of diverse heterocyclic motifs. Being a promising biocompatible nanoparticle, this catalyst has an important contribution in the fields of synthetic chemistry and medicinal chemistry.

TFA/TBHP-promoted oxidative cyclisation for the construction of tetracyclic quinazolinones and rutaecarpine

An efficient TFA/TBHP-promoted oxidative cyclisation of readily available isatins with 1,2,3,4-tetrahydroisoquinolines has been firstly developed. The potential utility of this strategy was demonstrated by one-step synthesis of a natural alkaloid Rutaecarpin.

Copper-catalyzed three-component reaction of N-heteroaryl aldehydes, nitriles, and water

An efficient and straightforward method for the synthesis of N-heteroaroyl imides has been successfully developed involving a copper-catalyzed radical-triggered three-component reaction of N-heteroaryl aldehydes, nitriles, and water. Mechanistic studies indicate that the reaction may undergo a radical-triggered Ritter-type reaction in which water serves as the oxygen source for the formation of the C-O bond. The reaction has advantages such as a broad substrate scope for the N-heteroaryl aldehydes, atom economy, and simple operation.

Silyl radical initiated radical cascade addition/cyclization: synthesis of silyl functionalized 4H-pyrido[4,3,2-gh]phenanthridin-5(6H)-ones

A cyclization cascade initiated by the addition of a silyl radical to an electron-deficient carbon-carbon double bond of N-arylacrylamides, followed by intramolecular cyano group insertion and homolytic aromatic substitution has been reported. In the presence of di-lauroyl peroxide (LPO), under metal-free conditions, several readily available hydrosilanes were successfully used as the source of silyl radicals and a series of silyl functionalized 4H-pyrido[4,3,2-gh]phenanthridin-5(6H)-ones were obtained in moderate to good yields.

Synthesis of Diverse Boron-Handled N-Heterocycles via Radical Borylative Cyclization of N-Allylcyanamides

A synthetic method based on radical borylation/cyclization cascades of N-allylcyanamides was developed to construct diverse boron-substituted N-heterocycles. In the reaction process, the N-heterocyclic carbene-boryl radical underwent a chemo- and regioselective addition to the alkene moiety, followed by cyclization with the N-cyano group. The resulting amide-iminyl radical intermediates underwent further reactions to afford various boron-tethered N-heterocyclic molecules. Further transformations to access synthetically useful building blocks were also demonstrated.

Synthesis of trifluoroalkyl or difluoroalkyl phenanthridine derivatives via cascade reaction using an intramolecular cyano group as a radical acceptor under photoredox catalysis

In the presence of Ru(phen)₃Cl₂ or fac-Ir(ppy)₃ under visible-light irradiation, the addition of fluorinated radicals to N-arylacrylamides followed by an intramolecular cyano group insertion cascade cyclization process produced the target compounds in moderate to good yields.

An access to 1,3-azasiline-fused quinolinonesviaoxidative heteroannulation involving silyl C(sp3)–H functionalization

A Mn-promoted intermolecular oxidative heteroannulation ofN-(2-cyanoaryl)-acrylamides with tertiary silanes toward 1,3-azasiline-fused quinolinones is presented.

Construction of a 4H-pyrido[4,3,2-gh]phenanthridin-5(6H)-one skeleton via a catalyst-free radical cascade addition/cyclization using azo compounds as radical sources

The new radical addition/cyano insertion/homolytic aromatic substitution cascade reaction initiated by the thermal homolysis of azo compounds under catalyst-free conditions produced polycyclic phenanthridine derivatives.

Photoredox Catalysis: Construction of Polyheterocycles via Alkoxycarbonylation/Addition/Cyclization Sequence

A novel visible-light-induced cascade reaction for the preparation of ester-functionalized polyheterocycles was developed under metal-free conditions, which was initiated by an intermolecular radical addition to a carbon-carbon double bond of N-arylacrylamide derivatives using alkyl carbazate as the ester source followed by cyano-mediated cyclization. The desired phenanthridine derivative products were isolated in moderate to high yields with broad substrate scope.

An I2-mediated cascade reaction of 2'-bromoacetophenones with benzohydrazides/benzamides leading to quinazolino[3,2-b]cinnoline or tryptanthrin derivatives

An efficient and facile protocol for the synthesis of quinazolinone-fused tetracyclic compounds through an iodine-mediated one-pot cascade reaction of 2'-bromoacetophenones with 2-aminobenzohydrazides or 2-aminobenzamides is reported. With 2-aminobenzohydrazides as the substrates, the reaction gave 5H-quinazolino[3,2-b]cinnoline-7,13-diones in moderate to good yields under metal-catalyst-free conditions. With 2-aminobenzamides as the substrates and CuBr as the catalyst, on the other hand, it afforded tryptanthrin derivatives with good efficiency. Mechanistically, the formation of the tetracyclic systems is initiated by iodination and oxidation of 2'-bromoacetophenones followed by a cascade procedure consisting of cyclocondensation, aromatization and intramolecular cyclization of the in situ formed 2-bromoarylglyoxals with 2-aminobenzohydrazides or 2-aminobenzamides, respectively.

Metal-free sequential decarbonylative annulation of N-cyanamides for the construction of 2,3-dihydropyrrolo[2,1-b]quinazolin-9(1H)-ones

A convenient metal-free sequential decarbonylative annulation of unactivated alkenes for the construction of quinazolinones and dihydroisoquinolinones has been developed.

I2-Catalyzed cross dehydrogenative coupling: rapid access to benzoxazinones and quinazolinones

An efficient and applicable I₂-catalyzed intramolecular dehydrogenative C–O/C–N coupling reaction has been developed for the first time to provide both benzoxazinones and quinazolinones.

Synthesis of quinazolinones via radical cyclization of α-azidyl benzamides

Under visible light irradiation with N-bromosuccinimide, α-azidyl benzamides can be transformed into quinazolinones in high efficiency via cascade radical processes.

Visible-light-promoted iminyl radical formation from vinyl azides: synthesis of 6-(fluoro)alkylated phenanthridines

An efficient strategy assisted by visible-light-promoted iminyl radical formation has been developed for the synthesis of 6-(fluoro)alkylated phenanthridine derivatives. In the reactions, addition of alkyl and trifluoromethyl radicals onto vinyl azides gives iminyl radicals, which then undergo intramolecular homolytic aromatic substitution leading to phenanthridines. These reactions can be carried out under mild conditions with high chemical yields and broad substrate scope.