Visible-Light Photosynthesis of CHF2 /CClF2 /CBrF2 -Substituted Ring-fused Quinazolinones in Dimethyl Carbonate

Photocatalytic decarboxylation of free carboxylic acids and their functionalization

Visible light mediated decarboxylative functionalization of carboxylic acids and their derivatives has recently emerged as a novel and powerful toolkit for small molecule activation in diverse carbon-carbon and carbon-hetero bond forming reactions. Naturally abundant highly functionalized bench-stable carboxylic acid analogs have been employed as promising alternatives to non-trivial organometallic reagents for mild and eco-benign synthetic transformation with traceless CO2 by-products. In this highlight article, we focus on the development of various photodecarboxylative functionalization strategies along with intra/inter-molecular cyclization via concerted single electron transfer (SET) or energy transfer (ET) pathways. Moreover, widely explored carboxylic acids are systematically classified here into four categories; i.e., α-keto, aliphatic, α,β-unsaturated, and aromatic analogs for a concise overview to the readership. The association of decarboxylative radical species with coupling partners to construct C-C and C-N/O/S/P/X bonds for each analogous acid has been presented in brief.

Metal-free synthesis of 1,1-dimethyl-2,2,2-trifluoroethyl substituted quinazolinones via tandem radical cyclization of quinazolin-4(3H)-ones with 3,3,3-trifluoro-2,2-dimethylpropanoic acid

A metal-free (NH4)2S2O8-mediated decarboxylative trifluoromethylation reaction of alkenes with 3,3,3-trifluoro-2,2-dimethylpropionic acid has been proposed. This method offers a novel route for the direct synthesis of a series of CMe2CF3-containing quinazolinones from basic chemical raw materials. The reaction mechanism was studied by a radical trapping test and DFT methods, verifying an oxidation-triggered cascade process promoted by the CMe2CF3 radicals. This strategy provides advantages such as high yield, wide substrate compatibility, and high atom economy.

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.

Reversal of the Regioselectivity of Iron-Promoted Hydrogenation and Hydrohalogenation of gem-Difluoroalkenes

The reaction regioselectivity of gem-difluoroalkenes is dependent on the intrinsic polarity. Thus, the reversal of the regioselectivity of the addition reaction of gem-difluoroalkenes remains a formidable challenge. Herein, we described an unprecedented reversal of regioselectivity of hydrogen atom transfer (HAT) to gem-difluoroalkenes triggered by Fe-H species for the formation of difluoroalkyl radicals. Hydrogenation of the in situ generated radicals gave difluoromethylated products. Mechanism experiments and theoretical studies revealed that the kinetic effect of the irreversible HAT process resulted in the reversal of the regioselectivity of this scenario, leading to the formation of a less stable α-difluoroalkyl radical regioisomer. On basis of this new reaction of gem-difluoroalkene, the iron-promoted hydrohalogenation of gem-difluoroalkenes for the efficient synthesis of aliphatic chlorodifluoromethyl-, bromodifluoromethyl- and iododifluoromethyl-containing compounds was developed. Particularly, this novel hydrohalogenation of gem-difluoroalkenes provided an effect and large-scale access to various iododifluoromethylated compounds of high value for synthetic application.

Photocatalytic cyclization of 3-(2-isocyanophenyl)quinazolin-4(3H)-ones for the construction of quinoxalino[2,1-b]quinazolinones

A new kind of building unit, 3-(2-isocyanophenyl)quinazolin-4(3H)-ones, was designed and synthesized for the construction of novel quinoxalino[2,1-b]quinazolinones. The radical cyclization of 3-(2-isocyanophenyl)quinazolin-4(3H)-ones with ethers afforded ether-substituted tetracyclic quinoxalino[2,1-b]quinazolinones under photocatalytic and metal-free conditions. In the process, the isocyano accepts a carbon radical to give an imidoyl radical, which adds to the electron-deficient CN bond in quinazolin-4(3H)-one.

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.

Electrochemical-Induced C-N Bond Formation: A New Method to Synthesis (Z)-Quinazolinone Oximes Using Primary Amines and Quinazolin-4(3H)-one

A novel and highly selective electrochemical method for the synthesis of diverse quinazolinone oximes via direct electrooxidation of primary amines/C(sp2)-H functionalization of oximes has been developed. The reaction is conducted in an undivided cell under constant current conditions and is oxidant-free, open-air, and eco-friendly. Notably, the protocol shows good functional group tolerance, providing versatile quinazolinone oximes in good yields. Moreover, the mechanism is investigated through control experiments and cyclic voltammogram (CV) experiments.

Cyclizations of Alkenyl(Alkynyl)-Functionalized Quinazolinones and their Heteroanalogues: A Powerful Strategy for the Construction of Polyheterocyclic Structures

Quinazolin-4-one, its heteroanalogues, and derivatives represent an outstandingly important class of compounds in modern organic, medicinal, and pharmaceutical chemistry, as these molecular structures are noted for their wide synthetic and pharmacological potential. In the last years, ever-increasing research attention has been paid to quinazolinone derivatives bearing alkenyl and alkynyl substituents on the pyrimidinone nucleus. The original structural combination of synthetically powerful endocyclic amidine (or amidine-related) and exocyclic unsaturated moieties provides a driving force for cyclizations, which offer an efficient toolkit to construct a variety of fused pyrimidine systems with saturated N- and N,S-heterocycles. In this connection, the present review article is mainly aimed at systematic coverage of the progress in using alkenyl(alkynyl)quinazolinones and their heteroanalogues as convenient bifunctional substrates for regioselective annulation of small- and medium-sized heterocyclic nuclei. Much attention is paid to elucidating the structural and electronic effects of reagents on the regio- and stereoselectivity of the cyclizations as well as to clarifying the relevant reaction mechanisms.

Photochemical Difluoromethylation of Quinoxalin-2(1H)-ones with Difluoroacetic Anhydride and Pyridine N-Oxide

A novel photochemical difluoromethylation of quinoxalin-2(1H)-ones under catalyst-free conditions was achieved with difluoroacetic anhydride and pyridine N-oxide. The green and mild reaction conditions as well as readily attainable difluoroacetic anhydride provide a useful protocol to prepare C3-difluoromethylated quinoxalin-2(1H)-ones.

Recent Advances in Visible Light-Mediated Radical Fluoro-alkylation, -alkoxylation, -alkylthiolation, -alkylselenolation, and -alkylamination

In the last few years, many reagents and protocols have been developed to allow for the efficient fluorofunctionalization of a diverse set of scaffolds ranging from alkanes, alkenes, alkynes, and (hetero)arenes. The concomitant rise of organofluorine chemistry and visible light-mediated synthesis have synergistically expanded the fields and have mutually benefitted from developments in both fields. In this context, visible light driven formations of radicals containing fluorine have been a major focus for the discovery of new bioactive compounds. This review details the recent advances and progress made in visible light-mediated fluoroalkylation and heteroatom centered radical generation.

Metal-Free Photoinduced Hydrocyclization of Unactivated Alkenes toward Ring-Fused Quinazolin-4(3H)-ones via Intermolecular Hydrogen Atom Transfer

A visible-light-induced hydrocyclization of unactivated alkenes was developed using 3CzClIPN as the photocatalyst to generate substituted α-methyldeoxyvasicinones and α-methylmackinazolinones in moderate to good yields. An intermolecular hydrogen atom transfer with THF as the hydrogen source was involved. Mechanism studies indicated that the intramolecular addition of the in situ formed aminal radical to the unactivated alkene generated the polycyclic quinazolinone.

Merging Copper(I) Photoredox Catalysis and Iodine(III) Chemistry for the Oxy-monofluoromethylation of Alkenes

A simple process for the oxy-monofluoromethylation of alkenes is described. In combination with visible-light copper(I) photoredox catalysis, an easily accessible iodine(III) reagent containing monofluoroacetoxy ligands serves as a powerful source of a monofluoromethyl (CH₂ F) radical, enabling the step economical synthesis of γ-fluoro-acetates from a broad range of olefinic substrates under mild conditions. Applications to late-stage diversification of alkenes derived from complex molecules, amino acids and the synthesis of fluoromethylated heterocycles are also demonstrated.

Visible-Light-Induced Regioselective C-H Sulfenylation of Pyrazolo[1,5-a]pyrimidines via Cross-Dehydrogenative Coupling

A visible-light-induced cross-dehydrogenative methodology has been developed for the regioselective sulfenylation of pyrazolo[1,5-a]pyrimidine derivatives. Rose bengal, blue LEDs, KI, K₂S₂O₈, and DMSO are all essential for this photocatalytic transformation. The protocol is applicable for the synthesis of a library of 3-(aryl/heteroaryl thio)pyrazolo[1,5-a]pyrimidine derivatives with broad functionalities. The selectivity and scalability of the methodology have been also demonstrated. Moreover, the efficiency of this strategy for sulfenylation of pyrazoles, indole, imidazoheterocycles, and 4-hydroxy coumarin has been proven. The mechanistic investigation revealed the radical-based mechanism and formation of diaryl disulfide as a key intermediate for this cross-dehydrogenative coupling reaction.

Visible-Light-Induced Difluoroalkylation of Alkenes and Alkynes with Fluoro-Containing Hypervalent Iodane (III) Reagents Under Photo-Catalyst-Free Conditions

A visible-light-induced difluoroalkylation of unactivated alkenes by fluoro-containing hypervalent iodine-based difluoroalkylation reagent was achieved for the first time under photo-catalyst-free conditions. Moreover, the same reaction conditions were applicable to the difluoroalkylation of alkynes to give the hydrodifluoroalkylation products in moderate to excellent yields. The readily available reagent, broad substrate scope, and photo-catalyst-free conditions make this protocol an efficient and environmental friendly method for the hydrodifluoroalkylation of alkenes and alkynes.

Hypervalent iodine(iii) promoted C–H/C–H amination/annulation tandem reactions: synthesis of benzimidazoles from simple anilines and aldehydes

A novel hypervalent iodine mediated cascade transformation of anilines and aldehydes to benzimidazoles was developed.

Visible-light-promoted radical cascade alkylation/cyclization: access to alkylated indolo/benzoimidazo[2,1-a]isoquinolin-6(5H)-ones

A new protocol is herein described for the direct generation of alkylated indolo/benzoimidazo[2,1-a]isoquinolin-6(5H)-one derivatives by using Hantzsch esters as alkylation radical precursors using a photoredox/K₂S₂O₈ system. This oxidative alkylation of active alkenes involves a radical cascade cyclization process and a sequence of Hantzsch ester single electron oxidation, C-C bond cleavage, alkylation, arylation and oxidative deprotonation.

Transition-metal-free radical difluorobenzylation/cyclization of unactivated alkenes: access to ArCF2-substituted ring-fused quinazolinones

A mild and efficient transition-metal-free radical difluorobenzylation/cyclization of unactivated alkenes toward the synthesis of difluorobenzylated polycyclic quinazolinone derivatives with easily accessible α,α-difluoroarylacetic acids has been developed. This transformation has the advantages of wide functional group compatibility, a broad substrate scope, and operational simplicity. This methodology provided a highly attractive access to pharmaceutically valuable ArCF₂-containing polycyclic quinazolinones.

Copper-Catalyzed Difluoroalkylation Reaction

This review describes recent advances in copper-catalyzed difluoroalkylation reactions. The RCF₂ radical is generally proposed in the mechanism of these reactions. At present, various types of copper-catalyzed difluoroalkylation reactions have been realized. According to their characteristics, we classify these difluoroalkylation reactions into three types.

Fast quinazolinone synthesis by combining enzymatic catalysis and photocatalysis

A fast and highly efficient method for the synthesis of functionalized quinazolinones by combining enzymatic catalysis and photocatalysis is reported. The α-Chymotrypsin catalyzed the cyclization of aldehyde and 2-aminobenzamide, which was subsequently followed by White LED-induced oxidation of 2-phenyl-2, 3-dihydroquinazolin-4(1H)-one to obtain quinazolinone. The reaction process was highly efficient with a reaction yield of 99% in just 2 h, and a wide range of quinazolinones could be synthesized. Furthermore, the plausible mechanism was investigated by control experiments and DFT calculations. This protocol provides an alternative synthetic route for the preparation of quinazolinone derivatives.

Visible-Light-Mediated Tandem Difluoromethylation/Cyclization of Alkenyl Aldehydes toward CF2H-Substituted Chroman-4-one Derivatives

An efficient and facile visible-light-mediated tandem difluoromethylation/cyclization of alkenyl aldehydes, with easily accessible and air-stable [Ph₃PCF₂H]⁺Br^- as the difluoromethylation reagent, has been established. A range of CF₂H-substituted chroman-4-one skeletons and their derivatives, such as 2,3-dihydroquinolin-4(1H)-ones, chroman, 3,4-dihydronaphthalen-1(2H)-one, 2,3-dihydrobenzofuran, and 2,3-dihydro-1H-inden-1-one, are efficiently produced in moderate to good yields with excellent chemoselectivity under mild reaction conditions.

Photoinduced Three-Component Difluoroalkylation of Quinoxalinones with Alkenes via Difluoroiodane(III) Reagents

An environmentally friendly strategy for the photocatalyzed three-component reaction between quinoxalinones, alkenes, and hypervalent iodine(III) reagents is disclosed. The new designed difluoroiodane(III) reagent shows excellent reactivity, providing a wide range of difluoroalkyl-substituted quinoxaline-2(1H)-ones in moderate to excellent yields under mild conditions. Experimental studies demonstrated that a difluoroalkyl radical intermediate was involved in this reaction.

Direct C(sp3)−H Difluoromethylation via Radical-Radical Cross-Coupling by Visible-Light Photoredox Catalysis

Herein, the radical-radical cross-coupling strategy for direct difluoromethylation of C(sp3)−H bond is reported. This transformation was readily accomplished under transition metal-free photoredox catalysis in the presence of 3 mol% of...

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,...

State of knowledge in photoredox-catalysed direct difluoromethylation

The combination of visible light photoredox catalysis with direct difluoromethylation has allowed the synthesis of a large choice of CF2H-containing value-added molecules under very mild reaction conditions.