Access to 4-substituted 3,4-dihydroquinolin-2(1H)-ones by an unusual radical cyclisation of a secondary amide

A novel route to 3,4-dihydroquinolin-2(1H)-ones involving two radical addition steps is reported, starting from readily accessible xanthates and N-aryl-3-butenamides.     

Superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids: synthesis of quinolin-2(1H)-one derivatives

The superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids by Bronsted superacids (CF₃SO₃H, HSO₃F) or strong Lewis acids AlX₃ (X=Cl, Br) results in the formation of 4-aryl quinolin-2(1H)-ones in quantitative yields. The vinyl triflates or vinyl chlorides may be formed as additional reaction products. The investigated amides in reactions with benzene give 4,4-diaryl 3,4-dihydroquinolin-2-(1H)-ones under the superelectrophilic activation. 4-Aryl quinolin-2(1H)-ones in POCl₃ are converted into 4-aryl 2-chloroquinolines. 4-Fluorophenyl-4-phenyl 3,4-dihydroquinolin-2-(1H)-one give N-formylation products in a yield of 79% under the Vilsmeier–Haack reaction conditions.     

Synthesis of 1H-pyrrolo[3,2-c]quinoline derivatives via palladium-catalyzed heteroannulation of 2-aryl-3-iodo-4-(phenylamino)quinolines and 4-(N,N-allylphenylamino)-2-aryl-3-iodoquinolines

Palladium(0)/copper iodide catalyzed Sonogashira cross-coupling of 2-aryl-3-iodo-4-(phenylamino)quinolines with terminal alkynes afforded series of 1,2,4-trisubstituted 1H-pyrrolo[3,2-c]quinolines in a single-step operation. Conversely, the 4-(N,N-allylphenylamino)-2-aryl-3-iodoquinoline derivatives were found to undergo PdCl₂(PPh₃)₂/CuI catalyzed intramolecular Heck reaction to yield the corresponding 1,3,4-trisubstituted 1H-pyrrolo[3,2-c]quinolines.     

Facile synthesis of 4-phenylquinolin-2(1H)-one derivatives from N-acyl-o-aminobenzophenones

An efficient synthesis of 4-phenylquinolin-2(1H)-one derivatives has been achieved in a one-pot reaction from N-acyl-o-aminobenzophenones 1a-c (a: acyl=acetyl; b: acyl=propanoyl; c: acyl=heptanoyl) using NaH as a base. Treatment of 1 with NaH provided the quinolones 2a-c with 62-83% yields, whereas the reaction in the presence of alkyl iodide (alkyl=methyl, ethyl, n-octyl) gave the corresponding N-alkylated quinolones 3a-g in 75-95% yields. The alkylation reaction of 4-phenylquinolin-2(1H)-one 2a with alkyl halide gave a mixture of N-alkylated and O-alkylated products. Comparison of IR and NMR data of the N-alkylated and O-alkylated compounds with those of 2a-c indicated that 2a-c exist as the lactam form.     

N-Arylation of 4-fluoro-5-trimethylsilyl-1H-pyrazole

The 1,3-dipolar cycloaddition reaction of fluoro(trimethylsilyl)acetylene prepared in situ with an excess of diazomethane smoothly proceeded to give the corresponding 4-fluoro-5-trimethylsilyl-1H-pyrazole in 84% yield. The copper iodide-catalyzed N-arylation of the fluorinated pyrazole with a variety of aryl iodides afforded N-aryl-4-fluoropyrazoles as desilylation products in good to excellent yields.     

Rapid access to 3-(N-substituted)-aminoquinolin-2(1H)-ones using palladium-catalyzed C-N bond coupling reaction

A series of 3-(N-substituted)-aminoquinolin-2(1H)-ones have been synthesized by the palladium-catalyzed C-N coupling reaction starting from 3-bromoquinolin-2-(1H)-ones. Various nucleophiles including amines, amides, sulfonamides, carbamates and ureas have been used successfully. In all the cases, the reactions take place rapidly in 1,4-dioxane and proceed in good to excellent yield using palladium acetate as a catalyst, Xantphos as a ligand and Cs₂CO₃ as a base.     

Efficient N-arylation of pyridazin-3(2H)-ones

A variety of substituted pyridazin-3(2H)-ones are directly N-arylated in good yield using lead tetraacetate/zinc chloride in benzene or in substituted benzenes including chloro- and bromobenzene.     

Trifluoroacetic acid: a more effective and efficient reagent for the synthesis of 3-arylmethylene-3,4-dihydro-1H-quinolin-2-ones and 3-arylmethyl-2-amino-quinolines from Baylis-Hillman derivatives via Claisen rearrangement

Trifluoroacetic acid has been discovered to be a highly effective and efficient reagent for the tandem Claisen rearrangement and cyclization reaction to yield 3-arylmethylene-3,4-dihydro-1H-quinolin-2-ones from compounds obtained from the S_N2 reaction between anilines and acetyl derivatives of Baylis-Hillman adducts of acrylates in the presence of DABCO. In contrast, similar compounds obtained from the acetyl derivatives of Baylis-Hillman adduct of acrylonitrile on treatment with trifluoroacetic acid directly furnish 3-arylmethyl-2-amino-quinoline via tandem Claisen rearrangement, cyclization and isomerization.     

A methodology for the synthesis of highly functionalized 2- and 4-aminoquinoline derivatives

A methodology for the synthesis of 2- and 4-aminoquinoline derivatives, which takes advantage of selective activation of 2- or 4-substituent of 2-methylsulfanyl-3-acyl-1H-quinolin-4-one 1, has been developed. Since a procedure for formation of 3-aminoquinolinones from the 4-quinolinone 1 was described previously, the new methodology comprises a general methodology for the selective syntheses of three isomeric 2-, 3- and 4-aminoquinoline derivatives starting with the common 4-quinolinone 1.     

Rational use of substituted N-allyl and N,N-diallylanilines in the stereoselective synthesis of novel 2-alkenyltetrahydro-1-benzazepines

Two new series of 1,4-epoxy-2-exo-vinyl(isopropenyl)tetrahydro-1-benzazepines and cis-2-vinyl(isopropenyl)-4-hydroxytetrahydro-1-benzazepines were prepared by an efficient three/four-step route from available substituted N,N-diallylanilines and mono N-allylanilines. The amino-Claisen rearrangement and the sequential oxidation/intramolecular 1,3-dipolar cycloaddition reactions were used as the key steps in this synthesis. All the synthesized compounds were fully characterized by IR, GC-MS and NMR techniques.     

Cyanamide: a convenient building block to synthesize 4-aryl-2-cyanoimino-3,4-dihydro-1H-pyrimidine systems via a multicomponent reaction

4-Aryl-2-cyanoimino-3,4-dihydro-1H-pyrimidine derivatives were prepared using a multicomponent reaction by reacting a mixture of arene or heteroarenecarbaldehyde, 1,3-dicarbonyl compounds, and cyanamide under acidic conditions. The novelty of this approach derives from its use of cyanamide as a building block in a four-component Biginelli-type reaction. Varying the reaction conditions led to the formation of either N-(2-imino-6-phenyl-1,3,5-oxadiazinan-4-ylidene) cyanamide or 3,4-dihydropyrimidin-2(1H)-one. The type of heterocycle skeleton synthesized depends on the nature of the acid catalyst as well as the reaction conditions employed.     

One-pot synthesis of 2-substituted furo[3,2-c]quinolines via tandem coupling-cyclization under Pd/C-copper catalysis

Pd/C-Cu catalyzed coupling reactions of 3-iodo-1H-quinolin-4-ones with a variety of terminal alkynes afforded furo[3,2-c]quinolines regioselectively in good to excellent yields. 3-Alkynyl quinolones were isolated under the same reaction conditions when the nitrogen of 3-iodo-1H-quinolin-4-one was substituted with an alkyl group.     

Trifluoromethyl-containing N-acylmethylenequinone imines as novel highly electrophilic agents

The strategy of searching for highly electrophilic agents in a class of chemically inert compounds - methylenequinone imines - was developed and successfully performed. The first representative of such electrophiles - N-acyl-α-methoxycarbonyl-α-trifluoromethyl-p-methylenequinone imine 6 - was synthesized. Its reactions with N-, O- and C-nucleophiles were investigated that gave various derivatives of α-trifluoromethyl-α-amino(oxy) acids as well as ß,ß,ß-trifluoropropionic acids. 3-Chloro-3-trifluoro-1,3-dihydroindol-2-ones were first obtained and their reactions with nucleophiles were studied with 1-aza-3-trifluoroindene-2-ones being formed as intermediates.     

N1,N3-Diacyl-3,4-dihydropyrimidin-2(1H)-ones: neutral acyl group transfer reagents

Readily available N1,N3-diacyl-3,4-dihydropyrimidin-2(1H)-ones efficiently acylate ammonia, primary and secondary amines to furnish primary, secondary and tertiary amides in good to excellent yields. The wide applicability of the procedure is demonstrated by running the reactions in a neutral medium, easy isolation of products, recycling of the innocuous by-product and chemoselectivity of the transformation.     

CuO nanoparticles catalyzed simple and efficient synthesis of 2,3-dihydroquinazolin-4(1H)-ones and quinazolin-4(3H)-ones under ultrasound irradiation in aqueous ethanol under ultrasound irradiation in aqueous ethanol

A CuO nanoparticle-catalyzed one-pot process has engineered for the preparation of diverse quinazolinones from the readily available isatoic anhydride, aldehydes and amine or ammonium. For amine substrates the reactions afford 2,3-dihydroquinazolin-4(1H)-ones in aqueous ethanol promoted by ultrasound irradiation. However, the ammonium substrates undergo intramolecular electron transfer and rearrangement yielding quinazolin-4(3H)-ones. The catalyst is recyclable four times without loss of substantial activity. Other remarkable features include the wide range of functional group tolerance (46 quinazolinones are synthesized and 9 of them are reported firstly), and providing moderate to excellent yield of the products under mild conditions.     

Synthesis of 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-ones via Pd-catalyzed regioselective cross-coupling reaction and cyclization

An efficient and novel route for the synthesis of 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-one 1 via palladium-catalyzed site-selective cross-coupling reaction and cyclization process was described. Reaction of 3-bromo-4-trifloxy-quinolin-2(1H)-one 3 with arylboronic acid catalyzed by PdCl₂(PPh₃)₂ afforded 3-bromo-4-aryl-quinolin-2(1H)-one 4, which then reacted with 2-ethynylaniline 5 via Pd-catalyzed Sonogashira coupling and CuI-mediated cyclization leading to the desired 1H-indol-2-yl-(4-aryl)-quinolin-2(1H)-one 1 in good yields.     

New synthesis of N-substituted benz[g]isoquinoline-3,5,10(2H)-triones

Various N-substituted benz[g]isoquinoline-3,5,10(2H)-triones 7 were prepared starting from vitamin K₃ (menadione) 9. The key steps involve substitution of a benzylic bromide by a primary amine and intramolecular condensation across the ester moiety of a (3-bromomethyl-naphth-2-yl)acetate 8 followed by oxidation with cerium(IV) ammonium nitrate (CAN) and spontaneous dehydrogenation, resulting in the title compounds 7. A selection of the synthesised new compounds was tested in vitro against Mycobacterium tuberculosis.     

A facile synthesis of 2-[1-(dialkylamino)alkyl]-4H-3,1-benzoxazin-4-ones by the reaction of 1,1-dimethylethyl 2-isocyanobenzoates with N,N-dialkyliminium iodides

A convenient synthetic approach to 2-[1-(dialkylamino)alkyl]-4H-3,1-benzoxazin-4-ones has been developed. Thus, 1,1-dimethylethyl 2-isocyanobenzoates, which can be readily prepared from 2-nitrobenzoic acids by a simple four-step sequence, react with N,N-dialkyliminium iodides without using any catalysts under mild conditions to give the desired products in generally fair-to-good yields.     

Suzuki-Miyaura cross-coupling of 2-aryl-6,8-dibromo-1,2,3,4-tetrahydroquinolin-4-ones and subsequent dehydrogenation and oxidative aromatization of the resulting 2,6,8-triaryl-1,2,3,4-tetrahydroquinolin-4-ones

Dichlorobis(triphenylphosphine)palladium(II)/tricyclohexylphosphine-catalyzed Suzuki-Miyaura cross-coupling of the 2-aryl-6,8-dibromo-1,2,3,4-tetrahydroquinolin-4-ones with arylboronic acids afforded the corresponding 2,6,8-triaryl-1,2,3,4-tetrahydroquinolin-4-ones, exclusively. The latter was subjected to thallium(III) p-tolylsulfonate (TTS) in dimethoxyethane under reflux or to molecular iodine in methanol at reflux to afford the 2,6,8-triarylquinolin-4-(1H)-ones and 2,6,8-triaryl-4-methoxyquinoline derivatives, respectively.     

The reaction of 2-(1-hydropolyfluoro-1-alkenyl)-4H-3,1-benzoxin-4-ones with dinucleophilic reagents: a convenient route to fluoroalkylated nitrogen-containing tricyclic compounds

The reactions of 2-(1-hydropolyfluoro-1-alkenyl)-4H-3,1-benzoxin-4-ones (2) with hydrazine hydrate and phenyl hydrazine were investigated. The reaction of 2 with hydrazine hydrate in ethanol under reflux condition readily gave 2-fluoroalkyl-4H-pyrazolo[5,1-b]quinazolin-9-ones (3) in high yields. The reaction of 2 with phenyl hydrazine, however, resulted in the formation of 2-(2-phenyl-5-fluoroalkyl-2H-pyrazol-3-yl) benzoic acids (7). Further treatment of 7 with PPA gave 1-phenyl-4,9-dihydro-3-fluoroalkyl-1H-pyrozolo[3,4-b]quinolin-4-ones (4) in 65-80% overall yields.