Base-promoted regioselective synthesis of 1,2,3,4-terahydroquinolines and quinolines from N-boc-3-piperidone

An efficient synthesis of 1,2,3,4-tetrahydroquinolines with donor and acceptor group has been delineated by base mediated ring transformation of 6-aryl-4-substituted-2H-pyran-2-one-3-carbonitriles by N-boc-3-piperidone followed by consecutive deprotection of Boc group under acidic conditions. This reaction involves 2 new bond formations namely C4a-C5 and C8a-C8 in order to create the nucleus. Various donor and acceptor functional groups like aryl, heteroaryl, nitrile, methylsulfanyl and secondary amine were installed in 1,2,3,4-tetrahydroquinolines. We extended our approach to synthesize the fused 1,2,3,4-tetrahydroquinolines by using 2-oxobenzo[h]chromenes as precursor. Further, we synthesized fused and isolated quinolines through aromatization of 1,2,3,4-tetrahydroquinolines by DDQ in excellent yields. Single-crystal X-ray analysis of the Boc protected tetrahydroisoquinoline 6t showed the steric hindrance between N-Boc and aryl group.     

Synthesis of 7-(2-R-pyrimidin-4-yl)- and 7-(2-R-[1,2,4]triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidin-7-yl)-2,2,4,6-tetramethyl-1,2,3,4-tetrahydroquinolines

Cyclization of 3-(dimethylamino)-1-(2,2,4,6-tetramethyl-1,2,3,4-tetrahydroquinolin-7-yl)prop-2-en-1-one with carboximidamides, guanidines, and 1,2,4-triazol-5-amines afforded a number of new 2,2,4,6-tetramethyl-7-(2-R-pyrimidin-4-yl)-1,2,3,4-tetrahydroquinolines and 2,2,4,6-tetramethyl-7-(2-R-[1,2,4]triazolo-[1,5-a]pyrimidin-7-yl)-1,2,3,4-tetrahydroquinolines.     

Pd(II)-catalyzed oxidative cyclization reaction for the preparation of 2-substituted 1,2,3,4-tetrahydroquinolines with halide functionality

The first Pd(II)-catalyzed oxidative cyclization reaction was developed for preparation of 2-substituted 1,2,3,4-tetrahydroquinolines from olefinic tosylamides. Under the optimized conditions, up to 86% yield was obtained. This reaction provides direct and easy access to 2-substituted 1,2,3,4-tetrahydroquinolines with halide functionality.     

Imino Diels-Alder Reactions: Efficient Synthesis of 2-Aryl-4-(2′-oxopyrrolidinyl-1′)-1,2,3,4-tetrahydroquinolines catalyzed by Antimony(III) Sulfate

Antimony(III) sulfate is found to catalyze the imino Diels-Alder reaction of Schiff’s bases with N-vinylpyrrolidin-2-one to afford 2-aryl-4-(2′-oxopyrrolidinyl-1′)-1,2,3,4-tetrahydroquinolines. One-pot synthesis of 1,2,3,4-tetrahydroquinolines from 3-nitro benzaldehyde and aromatic amines with N-vinylpyrrolidin-2-one catalyzed by antimony(III) sulfate is also reported. This catalyst is inexpensive, easily available, and it was also found that catalyst could be recovered quantitatively and reused without much loss of catalytic activity.     

Highly diastereoselective synthesis of new heterolignan-like 6,7-methylendioxy-tetrahydroquinolines using the clove bud essential oil as raw material

The diastereoselective synthesis toward novel heterolignan-like 2-aryl-4-(4-hydroxy-3-methoxyphenyl)-6,7-methylendioxy-1,2,3,4-tetrahydroquinolines using for the first time clove bud essential oil as a renewable material was carried out. The synthetic protocol consisted of the hydrodistillation of dried flower buds, the solid base-catalyzed isomerization of the obtained essential oil enriched with eugenol in order to give isoeugenol and its participation, as a chemical reagent (dienophile) in the BF₃·OEt₂-catalyzed three component Povarov reaction, without previous purification. Final products were obtained as racemic mixtures of new trans-2,4-diaryl-r-3-Me-1,2,3,4-tetrahydroquinolines in moderate to good yields.     

Imino <Emphasis Type="Italic">Diels-Alder</Emphasis> Reactions: Efficient Synthesis of 2-Aryl-4-(2′-oxopyrrolidinyl-1′)-1,2,3,4-tetrahydroquinolines catalyzed by Antimony(III) Sulfate

Summary. Antimony(III) sulfate is found to catalyze the imino Diels-Alder reaction of Schiff’s bases with N-vinylpyrrolidin-2-one to afford 2-aryl-4-(2′-oxopyrrolidinyl-1′)-1,2,3,4-tetrahydroquinolines. One-pot synthesis of 1,2,3,4-tetrahydroquinolines from 3-nitro benzaldehyde and aromatic amines with N-vinylpyrrolidin-2-one catalyzed by antimony(III) sulfate is also reported. This catalyst is inexpensive, easily available, and it was also found that catalyst could be recovered quantitatively and reused without much loss of catalytic activity.     

Radical cation salts induced domino reaction of anilines with enol ethers:Synthesis of 1,2,3,4-tetrahydroquinoline derivatives

A domino reaction of anilines with cyclic and acyclic enol ethers induced by catalytic amounts of TBPA^·+（5 mol%） was investigated and a series of 2,4-disubstituted-1,2,3,4-tetrahydroquinolines were synthesized.Different from cyclic enol ethers, when acyclic enol ethers were used in the reaction,they serve as surrogates of acetaldehyde,producing a series of 2-methyl-4- anilino-1,2,3,4-tetrahydroquinolines.A single electron transfer mechanism was proposed to rationalize the products formation.     

CAN-catalyzed three-component reaction between anilines and alkyl vinyl ethers: stereoselective synthesis of 2-methyl-1,2,3,4-tetrahydroquinolines and studies on their aromatization

The CAN-catalyzed reaction between anilines and vinyl ethers at room temperature provides a convenient and efficient access to 4-alkoxy-2-methyl-1,2,3,4-tetrahydroquinolines. This reaction is stereoselective, favouring a cis arrangement for the alkoxy and methyl groups, and involves a three-component process that leaves a molecule of alcohol as the only side product. 2-Methylquinoline derivatives were efficiently prepared from 4-alkoxy-2-methyl-1,2,3,4-tetrahydroquinolines by Pd-C-promoted dehydrogenation.     

An efficient synthesis of optically pure (S)-2-functionalized 1,2,3,4-tetrahydroquinoline

Using a copper-catalyzed coupling reaction of amino acid and aryl halide, followed by intramolecular cyclization of N-aryl-1-hydroxyl-3-propylamines under the Swern’s condition as the key steps, (S)-2-hydroxymethyl-1,2,3,4-tetrahydroquinoline was synthesized as an example of optically pure 2-functionalized 1,2,3,4-tetrahydroquinolines.     

Efficient dehydrogenation of 1,2,3,4-tetrahydroquinolines mediated by dialkyl azodicarboxylates

Various dialkyl azodicarboxylates were investigated for the dehydrogenation of 1,2,3,4-tetrahydroquinolines to quinolines. The dehydrogenation rates varied according to the electronic and steric nature of the used dialkyl azodicarboxylates. Among solvents screened with diethyl azodicarboxylate, chloroform exhibited superior results to others. A variety of 1,2,3,4-tetrahydroquinolines underwent the present dehydrogenation to produce the corresponding quinolines. Diethyl hydrazodicarboxylate, which is a reduced species of diethyl azodicarboxylate, was easily separated for recycle.     

Synthesis of 1,2,3,4-tetrahydroquinolines and 1,2,3,4-tetrahydro- 1,6-naphthyridines by a directed lithiation reaction

N-(tert-butoxycarbonyl)anilines (7), are easily converted in a one pot reaction sequence into the N- (tert-butoxycarbonyl)-1,2,3,4-tetrahydroquinolines (8), by directed ortho lithiation followed by reaction with 1- chloro-3-iodopropane, hence providing a new versatile quinoline ring nucleus synthesis. In an analogous reaction 2-N-(tert-butoxycarbonyl)- and an 2-N-(pivaloylamino) pyridine are converted to 1,2,3,4-tetrahydro-1,6- naphthyridines.     

Reactions of N- and C-Alkenylanilines: III. Synthesis and Cyclization of Substituted 2-(1-Methyl-2-butenyl)anilines

Reactions of substituted 2-(1-methyl-2-butenyl)anilines with iodine result in cyclization and formation of 3-iodo-1,2,3,4-tetrahydroquinolines; N-methylsulfonyl-2-(1-methyl-2-butenyl)anilines give rise exclusively to the corresponding 2-(1-iodoethyl)-3-methyl-2,3-dihydroindoles.     

Visible-Light-Induced Synthesis of 1,2,3,4-Tetrahydroquinolines through Formal [4+2] Cycloaddition of Acyclic α,β-Unsaturated Amides and Imides with N,N-Dialkylanilines

1,2,3,4-Tetrahydroquinolines should be applicable to the development of new pharmaceutical agents. A facile synthesis of 1,2,3,4-tetrahydroquinolines that is achieved by a photoinduced formal [4+2] cycloaddition reaction of acyclic α,β-unsaturated amides and imides with N,N-dialkylanilines under visible-light irradiation, in which a new Ir^III complex photosensitizer, a thiourea, and an oxidant act cooperatively in promoting the reaction, is reported. The photoreaction enables the synthesis of a wide variety of 1,2,3,4-tetrahydroquinolines, while controlling the trans/cis diastereoselectivity (>99:1) and constructing contiguous stereogenic centers. A chemoselective cleavage of an acyclic imide auxiliary is demonstrated.     

InCl3-catalyzed allylic Friedel-Crafts reactions toward the stereocontrolled synthesis of 1,2,3,4-tetrahydroquinolines

Allyl chlorides tethered to an N-aryl moiety readily undergo InCl(3)-catalyzed Friedel-Crafts reactions to furnish highly enantiomerically enriched 1,2,3,4-tetrahydroquinolines with good yields and excellent diastereoselectivity.     

An efficient synthesis of enantiomerically pure aromatic-fused N-containing heterocycles from common chiral aziridines

An efficient synthesis of enantiomerically pure aromatic-fused N-containing heterocycles was successfully achieved via Pd-catalyzed intramolecular C-N bond formation between the nitrogen originated from the aziridine and the halogen containing aromatic carbon. This reaction has a broad substrate scope to provide various enantiomerically pure (3,4-dihydro-2H-benzo[b][1,4]oxazin-3-yl)methanols, 2-hydroxymethyl-1,2,3,4-tetrahydroquinolines and (1,2,3,4-tetrahydroquinoxalin-2-yl)methanols from common chiral aziridines in good yields.     

Synthesis of new hydroquinolinecarbaldehydes

A number of new N-alkyl-6(8)-formylhydroquinolines have been synthesized. The Vilsmeier—Haack reaction of 7(8)-substituted N-alkyl-1,2-dihydroand N-alkyl-1,2,3,4-tetrahydroquinolines led to 6-formylhydroquinolines, whereas N-methyl-8-formylhydroquinolines were formed in the case of 6-substituted N-methyl-1,2-dihydroand N-methyl-1,2,3,4-tetrahydroquinolines.

     

Non-steroidal antiinflammatory agents. 3. Synthesis of 3-hydroxy-3-hydroxyphenyl-2,4-dioxo-1,2,3,4-tetrahydroquinolines

The acid-catalyzed condensation of quinisatines 5a-c or their aminals 4a-c with phenols 6a-i led to a number of 3-hydroxy-3-hydroxyphenyl-2,4-dioxo-1,2,3,4-tetrahydroquinolines 7a-s which were considered as potential antiinflammatory agents.     

Ionic diamine rhodium complex catalyzed hydroaminomethylation of 2-allylanilines

Ionic diamine rhodium complexes catalyze the hydroaminomethylation of 2-allylanilines. The reaction involves initial hydroformylation followed by reductive amination, which provides direct access to 1,2,3,4-tetrahydroquinolines and 2,3,4,5-1H-1-benzazepines.     

Synthesis and structure of 2-aryl-2,4-dimethyl-1,2,3,4-tetrahydroquinolines and 1,3-disubstituted indenes

It has been shown that the intramolecular cyclization of N-(1-arylbutenyl)arylamines under acid catalysis conditions may proceed in two directions with the formation of 2-aryl-2,4-dimethyl-1,2,3,4-tetrahydroquinolines and 1,3 disubstituted indenes.     

Indole chemistry

A new method of synthesizing lilolidenes (1,7-trimethyleneindoles), by reacting 1,2,3,4-tetrahydroquinolines with α-bromoketones, is given. PMR spectra of 2-substituted lilolidenes are obtained, and the effects of chemical substituents at positions 1 and 3 in the lilolidene ring on the chemical shift of protons is considered.