Reactions of 1,2-dihydroquinolines

The addition of benzene to 2,2,4-trimethyl-1,2-dihydroquinoline (I) in the presence of AlCl₃ requires prior protonation or acylation of the amino group. Electron-donor substituents in the benzene ring of I hinder the reaction. The addition of halobenzenes proceeds under more severe conditions to give only para-substituted 4-aryl-2,2,4-trimethyl-1,2,3,4-tetrahydroquinolines.See [1,2] for communications I and II.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 795–797, June, 1971.     

Indole derivatives

A mixture of isomeric 2,2,4-trimethyl- and 2,4,4-trimethyl-1,2,3,4-tetrahydro--carbolines is formed as a result of the Fischer cyclization of 2,2,6-trimethyl-4-piperidone arylhydrazones.See [1] for communication XXXVI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1070–1073, August, 1971.     

The mystery of the discolored flints. New molecules turn prehistoric lithic artifacts blue

Prehistoric artifacts turning blue in the store rooms of the Natural History Museum in Verona, Italy recently raised serious issues for heritage materials conservation. Our analytical investigation showed that the unusual discoloration process of the flint tools is caused by the surface presence of at least three previously unknown pigmenting molecules of the triphenylmetane dyes class: 6-(bis(2,2,4-trimethyl-1,2-dihydroquinolin-6-yl)methylene)-2,2,4-trimethyl-2,6-dihydroquinolinium and its hydrogenated derivatives 2,2,4-trimethyl-6-((2,2,4-trimethyl-1,2,3,4-tetrahydroquinolin-6-yl)(2,2,4-trimethyl-1,2-dihydroquinolin-6-yl)methylene)-2,6-dihydroquinolinium and 6-(bis(2,2,4-trimethyl-1,2,3,4-tetrahydroquinolin-6-yl)methylene)-2,2,4-trimethyl-2,6-dihydroquinolinium. The peculiar formation of the molecules is possibly catalyzed within the silica pore surface starting from a well-known rubber stabilizer 2,2,4-trimethyl-1,2-dihydroquinoline released by the plastic pads flooring the storing cabinets. The investigated reaction and its surprising blue product represent a case study of the application of modern materials science to conservation and a serious warning towards the unpredictable challenges faced in the preservation of our cultural heritage.     

Indole derivatives

Reduction of 2,2,4-trimethyl-, 2,2,4,4,6-pentamethyl-, and 2,2, 4,4,9-pentamethyl-1,2,3,4-tetrahydro-γ-carboline gives 1,2,3,4, 4a,9a-hexahydro-γ-carbolines, along with products of destructive hydrogenation. The sole reduction product of 2,2,3,4,4-pentamethyl-1,2,3,4-tetrahydro-γ-carboline is 2-(β-methylaminoisobutyl)indoline.     

Reactions of 1,2-dihydroquinolines

2,2,4-Trimethyl-1,2-dihydroquinolines readily add alkylbenzenes under the influence of aluminum chloride to form 2,2,4-trimethyl-4-(p-alkylphenyl)-1,2,3,4-tetrahydroquinolines.See [1] for Communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1512–1514, November, 1970.     

Research on polyfunctional oxides

N,N-Diethylcarbamoyl-4,5-epoxy-2-hexenoic acid reacts with ketones in the presence of anhydrous FeCl₃ to give 2,2,4-trialkyl-5-[2-N,N-diethylcarbamoyl(vinylene)]-1,3-dioxolane. 2,2,4-Trimethyl-5-(1-propenyl-3-hydroxy)-1,3-dioxolane is formed in the reduction of 2,2,4-trimethyl-5-[2-carbethoxy(vinylene)]-1,3-dioxolane withlithium aluminum hydride.     

An intramolecular charge-transfer complex in hydrogenated quinolines

The IR spectra of 6R-2,2,4-trimethyl-1,2-dihydroquinolines (I) and 6-R2,2,4-ttimethyl-1,2,3,4-tetrahydroquinolines (II) with R=H, CH₃, OCH₃, and OC₂H₅ and those of their acetyl derivatives have been studied. The change in the intensity and the frequencies of the bands of the stretching vibrations of the C–N and C=C bonds and the ring with a change in the structure of the molecule have been considered. The considerable differences in the IR and UV spectra of I and II are explained by the fact that in the I series the interaction between the pelectrons of the nitrogen and the -electrons of the double bond (of the CTC type) and in the II series that of the -electrons of the nitrogen with the aromatic ring is predominant.     

Mechanism of Photoinduced Addition of Water and Methanol to the Double Bond of 1,2-Dihydroquinolines

The kinetics and mechanism of photoinduced addition of water and methanol to the double bond of 2,2,4-trimethyl-1,2-dihydroquinoline (DHQ) bearing different substituents in the 6- and 8-positions and N-methylated DHQ were studied by flash photolysis. The reaction affords corresponding Markovnikov adducts, 4-hydroxy- and 4-methoxy-1,2,3,4-tetrahydroquinolines. On the basis of time-resolved experiments and the measurement of quantum yields of the reaction in media of different acidities or basicities, a general scheme of the reaction is suggested, which involves the formation of two intermediate species. The principal rate constants, activation parameters, and their dependence on substituents were determined.     

Pteridine. Teil LXXXII. Synthese und Reaktivität von Lumazin-7-sulfensäuren

Synthesis and Reactivity of Lumazine-7-sulfenic Acids The chemical synthesis of the pteridine-7-sulfenic acids 13 – 16 is described (Scheme 1). The 1,2,3,4-tetrahydro-1,3,6-trimethyl-2,4-dioxopteridine-7-sulfenic acid ( 14 ) was isolated as a stable crystalline solid. Its chemical reactivity was investigated and the physical properties determined. In the solid state, the S-oxide form 14A predominates, but in protic solvents the S-OH tautomer 14 exists most likely. In basic medium, the pteridine-7-sulfenate species is stable, whereas a low pH gives rise to a disproportionation to the disulfide 10 and the corresponding pteridine-7-sulfinic acid 37 (Scheme 4). Reaction of 14 with ethyl propiolate leads, under cis-addition, to 36 , oxidation with KMnO₄ forms 1,2,3,4-tetrahydro-1,3,6-trimethyl-2,4-dioxopteridine-7-sulfonic acid ( 38 ) and NaBH₄ reduction the corresponding 7-mercaptopteridine dione 18 (Scheme 4).     

Unexpected synthesis of azepino[4,3,2-cd]indoles from 4-aminoindoles

Unexpected regioselectivity for the Skraup-Doebner-Von Miller reaction was observed during the synthesis of quinolines from 4-aminoindoles and acetone in the presence of hydrochloric acid as a catalyst. The products were unambiguously assigned as 1-alkyl-3,5,5-trimethyl-5,6-dihydro-1H-azepino[4,3,2-cd]indoles instead of 2,2,4-trimethyl-2,7-dihydro-1H-pyrrolo[2,3-h]quinolones based on NMR spectroscopy and X-ray crystallographic analysis.     

Trimerization of aldehydes with one α-hydrogen catalyzed by sodium hydroxide

Trimerization of 2-methylpropanal (isobutyraldehyde) is a simple and effective method to synthesize 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl-1,3-pentanediol-3-monoisobutyrate which are often used as film forming auxiliaries in paints. The use of solid sodium hydroxide as a catalyst provides an excellent yield of above 85 % after the optimization of the reaction time and the catalyst dosage. Furthermore, trimerization of four other aldehydes with one α-hydrogen catalyzed by solid sodium hydroxide can also take place and the yield of 1,3-diol monoesters reaches 50–70 %. Trimerization of aldehydes with one α-hydrogen can be explained by a three-step reaction mechanism: (i) aldol condensation of aldehyde; (ii) crossed Cannizzaro reaction; and (iii) esterification of carboxylic acid and alcohol.     

Phase equilibria for systems containing dimethyl disulfide and diethyl disulfide with hydrocarbons at 368.15 K

Isothermal vapor–liquid equilibrium (VLE) for dimethyl disulfide + toluene, dimethyl disulfide + 2,2,4-trimethylpentane, dimethyl disulfide + 2,4,4-trimethyl-1-pentene, and diethyl disulfide + 2,2,4-trimethylpentane at 368.15 K were measured with a recirculation still. All systems exhibit positive deviation from Raoult's law. Dimethyl disulfide + toluene system shows only slight positive deviation from Raoult's law, while dimethyl disulfide + 2,2,4-trimethylpentane, dimethyl disulfide + 2,4,4-trimethyl-1-pentene, and diethyl disulfide + 2,2,4-trimethylpentane systems show larger positive deviation from Raoult's law. Maximum pressure azeotropes were found in systems: dimethyl disulfide + toluene (x₁ = 0.632, P = 66.4 kPa, T = 368.15 K), dimethyl disulfide + 2,2,4-trimethylpentane (x₁ = 0.311, P = 95.8 kPa, T = 368.15 K), and dimethyl disulfide + 2,4,4-trimethyl-1-pentene (x₁ = 0.295, P = 88.4 kPa, T = 368.15 K). No azeotropic behavior was observed in system diethyl disulfide + 2,2,4-trimethylpentane at 368.15 K. The experimental results were correlated with the Wilson model. Original UNIFAC was used to predict dimethyl disulfide + 2,2,4-trimethylpentane and diethyl disulfide + 2,2,4-trimethylpentane systems at 368.15 K. COSMO-SAC predictive model was used to predict infinite dilution activity coefficients for all systems measured. Liquid and vapor-phase composition were determined with gas chromatography. All VLE measurements passed the thermodynamic consistency tests applied. The activity coefficients at infinite dilution are also presented.     

Reaction of Zinc Enolates of Alkyl Esters of Substituted 4-Bromo-3-Oxoalkanoic Acids with Aldehydes

Zinc enolates formed from ethyl 4-bromo-2,2,4-trimethyl-3-oxopentanoate react under the conditions of one- of two-stage synthesis with aliphatic, unsaturated, or aromatic aldehydes to form 6-R-2,2,4,4-tetramethyl-2,3,5,6-tetrahydropyran-2,4-diones. Zinc enolates obtained from ethyl 4-bromo-2,2-dimethyl-3-oxopentanoate, -hexanoate, and -2,2,5-trimethyl-3-oxohexanoate under the similar conditions react with aliphatic or aromatic aldehydes to give mainly 5-R¹-6-R²-3,3-dimethyl-2,3,5,6-tetrahydropyran-2,4-diones as E or Z isomers or their mixtures. Zinc enolates generated from the ethyl 4-bromo-2,2-diethyl- or 2-benzyl-2-ethyl-3-oxobutanoates react with aromatic aldehydes to give ethyl 5-R-2-R-2-ethyl-3-oxo-4-pentenoates as E isomers.     

Synthesis and structure of the first representative of pentacoordinate C,O-chelates with a dipeptide fragment,the fluorosilane Ts—Gly—(S)-Pro—N(Me)CH2SiMe2F

A reaction of bicyclic 2-sila-5-piperazinone, 2,2,4-trimethyl-1,4-diaza-2-silabicyclo-[4.3.0]nonan-5-one containing a proline moiety, and N-tosylglycine acyl chloride with subsequent hydrolysis of the primary unstable product to the intermediate disiloxane and its treatment with BF₃?OEt₂ furnished a first representative of pentacoordinate C,O-chelate halosilanes with a dipeptide fragment, namely, Ts—Gly—(S)-Pro—N(Me)CH₂SiMe₂F.

     

Dissociation energies of O-H and N-H bonds in hybrid antioxidants

The dissociation energies of O-H and N-H bonds have been determined for ten aminophenoltype (HOArAmH) hybrid antioxidants. The bond dissociation energies D _O-H and D _N-H have been estimated from experimental kinetic data (rate constants of the reactions of peroxyl radicals with these antioxidants and their alkyl-substituted derivatives) by the intersecting-parabolas method. Kinetic data for the reactions of peroxyl radicals with HOArAmH, ROArAmH, and HOArAmR compounds were used. The following D _O-H and D _N-H values (kJ/mol) were obtained: for 4-hydroxydiphenylamine, D _O-H = 338.8 and D _N-H = 355.9; for 4-hydroxyphenyl-2-naphthylamine, D _O-H = 335.4 and D _N-H = 353.6; for 6-hydroxy-1,2-dihydro-2,2,4-tri-methylquinoline, D _O-H = 338.0 and D _N-H = 348.2; for 9-hydroxy-1,2-dihydro-2,3,4-trimethylquinoline, D _O-H = 329.7 and D _N-H = 383.3; for 6-hydroxy-1,2,3,4-tetrahydro-2,2,4-trimethylquinoline, D _O-H = 324.4 and D _N-H = 345.3; for 8-hydroxy-1,2,3,4-tetrahydro-2,2,4-trimethylquinoline, D _O-H = 329.4 and D _N-H = 380.6; for 5-hydroxyimidazole, D _O-H = 356.4 and D _N-H = 368.4; for 5-hydroxy-2-methylimidazole, D _O-H = 351.3 and D _N-H = 362.6; for 5-hydroxy-4,6-dimethylimidazole, D _O-H = 346.7 and D _N-H = 357.3; for 5-hydroxy-2,4,6-trimethylimidazole, D _O-H = 347.7 and D _N-H = 358.7.     

Sulfuration of 2,2,4-trimethyl-1,2,3,4-tetrahydroquinolines

Conclusions Substituted 2,2,4-trimethyl-1,2,3,4-tetrahydroquinolines upon reaction with a six-fold amount of sulfur at 210–220°C, similarly to dihydroquinolines, give the corresponding 4,5-dihydro-4,4-dimethyl-2,3-dithiolo[3,4-c]quinoline-1-thiones.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 191–192, January, 1989.     

“Reduced” Coumarin Dyes with an O‐Phosphorylated 2,2‐Dimethyl‐4‐(hydroxymethyl)‐1,2,3,4‐tetrahydroquinoline Fragment: Synthesis,Spectra, and STED Microscopy

Large Stokes‐shift coumarin dyes with an O‐phosphorylated 4‐(hydroxymethyl)‐2,2‐dimethyl‐1,2,3,4‐tetrahydroquinoline fragment emitting in the blue, green, and red regions of the visible spectrum were synthesized. For this purpose, N‐substituted and O‐protected 1,2‐dihydro‐7‐hydroxy‐2,2,4‐trimethylquinoline was oxidized with SeO₂ to the corresponding α,β‐unsaturated aldehyde and then reduced with NaBH₄ in a “one‐pot” fashion to yield N‐substituted and 7‐O‐protected 4‐(hydroxymethyl)‐7‐hydroxy‐2,2‐dimethyl‐1,2,3,4‐tetrahydroquinoline as a common precursor to all the coumarin dyes reported here. The photophysical properties of the new dyes (“reduced coumarins”) and 1,2‐dihydroquinoline analogues (formal precursors) with a trisubstituted C=C bond were compared. The “reduced coumarins” were found to be more photoresistant and brighter than their 1,2‐dihydroquinoline counterparts. Free carboxylate analogues, as well as their antibody conjugates (obtained from N‐hydroxysuccinimidyl esters) were also prepared. All studied conjugates with secondary antibodies afforded high specificity and were suitable for fluorescence microscopy. The red‐emitting coumarin dye bearing a betaine fragment at the C‐3‐position showed excellent performance in stimulation emission depletion (STED) microscopy.     

Role of steric hindrance in photoinduced proton transfer from solvent to excited molecules of 1,2-dihydroquinolines

It was shown that the photolysis of 1,2,6-trimethyl-1,2-dihydroquinoline (126TMDHQ) in water, methanol, ethanol, and isopropanol affords the corresponding adducts of water and the alcohols, unlike the case of 2,2,4-trimethyl-1,2-dihydroquinolines bearing the methyl, alkoxyl, and hydroxyl substituents in the 1-, 6-, and 8-positions, which were previously found to form adducts only in the presence of water and MeOH. The quantum yield of the 126TMDQ photolysis (Φ) in this solvent series changes as Φ_MeOH:Φ_EtOH:Φ_PrOH = 10:3:1. The results were rationalized in terms of the effect of steric hindrance caused by substituents on the heterocycle and increasing size of the alcohol alkyl group on proton transfer from the solvent to the 1,2-dihydroquinoline molecule in the excited singlet state. The existence of two adduct isomers was revealed. The preferential formation of one of the isomers was considered from the standpoint of carbocation accessibility to the solvent by nucleophilic attack.     

Nachweis von 6-Äthoxy-2,2,4-trimethyl-1,2-dihydrochinolin und p-Phenetidin nebeneinander

Zusammenfassung Das Antioxydans 6-Äthoxy-2,2,4-trimethyl-1,2-dihydrochinolin (I) enthält als Beimengungen p-Phenetidin und 6-Äthoxy-2,4-dimethylchinolin (II). p-Phenetidin kann neben I und II mittels 2,4-Dinitrofluorbenzol nachgewiesen werden. I gibt mit Natriumnitrit in saurem Medium eine Farbreaktion; damit kann es nachgewiesen werden. Dabei setzen sich p-Phenetidin und II nicht um. Außerdem kann I neben p-Phenetidin und II mit Chloramin T nachgewiesen werden.

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Detection of 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline and p-phenetidine in the presence of each other

Summary The antioxidant 6-ethoxy-2,2,4-trimethyl-1,2-dihydroquinoline (I) contains as admixturesp-phenetidine and 6-ethoxy-2,4-dimethylquinoline (II).p-Phenetidine can be detected in the presence of (I) and (I) by means of 2,4-dinitrofluorobenzene. (I) yields a color reaction with sodium nitrite in acid medium; hence it may be detected.p-Pheneteidine and (II) give no response. Furthermore (I) may be detected in the oresence ofp-phenetidine and (II) by means of chloramine T.

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