Photoaddition of water and methanol to 2,2,4,6-tetramethyl-1,2-dihydroquinoline

Products of the steady-state photolysis of 2,2,4,6-tetramethyl-1,2-dihydroquinoline (1) in water, methanol, and water—ethanol were isolated for the first time and identified by¹H and¹³C NMR spectroscopy, IR spectroscopy, and mass spectrometry. As a result of the photolysis, the molecule of the solvent is added to the double bond of the heterocycle with formation of 4-hydroxy- (2) or 4-methoxy-2,2,4,6-tetramethyl-1,2,3,4-tetrahydroquinoline (3) in water and methanol, respectively. Compounds2 and3 are converted gradually into1 in the dark. The rate of the back reaction depends on the solvent and the concentration of the product. Comparison of the products of the photolysis in methanol and hexane at 45 °C and of the azoisobutyronitrile-initiated oxidation of1 at the same temperature has shown that unlike the photolysis in hexane, aminyl radicals are not precursors of the product of the photolysis in methanol. The reaction proceedsvia an excited singlet state. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2072–2077, November, 1999.     

Reactivity of the carbocation generated in the photolysis of 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline toward azide ion

The reaction of the azide ion with the carbocation generated in the photolysis of 1,2,2,4,6-pentamethyl-1,2-dihydroquinoline in methanol was studied by pulse (conventional and laser) and steady-state photolysis techniques. The adduct of the azide ion was characterized by ¹H NMR spectrum. Experimental results were interpreted taking into account a competition between the addition of methanol and azide ion to the carbocation. The rate constants for the reaction of the azide ion with the carbocation (k _Az) were measured at 2—48 °C in a wide range of [N₃ ^–]₀ concentrations from 2·10^–7 to 0.1 mol L^–1 at different ionic strengths () of the solution. The resulting k _Az values are more than an order of magnitude lower than those for diffusional-controlled reactions and vary from 3.2·10⁸ ( = 0) to 4.5·10⁶ L mol^–1 s^–1 ( = 0.8 mol L^–1) in the presence of NaClO₄ (18 °C). The activation energy of addition of the azide ion to the carbocation is 21 kJ mol^–1, which is by 12 kJ mol^–1 lower than the activation energy of the reaction of the carbocation with methanol. The features of the reaction under study are discussed from the viewpoint of the structures of carbocations generated in the photolysis of dihydroquinolines.     

Effect of pH on kinetics of the decay of the radicals formed during photolysis of 2,2,4,6-tetramethyl-1,2-dihydroquinoline in aqueous and micellar solutions

Kinetics of the decay of the transient radicals formed from 2,2,4,6-tetramethyl-1,2-dihydroquinoline (TMQ) in aqueous and micellar solutions of sodium dodecyl sulfate were studied by flash photolysis as a function of pH. In aqueous and micellar solutions of TMQ the mechanism of the decay of the transient species and the reaction products are different from those in homogeneous organic solutions. The decay of the transient radicals follows first-order kinetics in the entire range of pH under consideration in both aqueous and micellar solutions. In aqueous solutions at pH 9–12, the decay rate constant decreases from 25.3 to 3.7 s⁻¹. In micellar solutions at different pH, different types of micellar catalysis were observed. At pH 1, the rate constant in a micellar solution is slightly lower than that in an aqueous solution. At pH 3–11, the decay rate constant increases (positive micellar catalysis). The apparent rate constant depends linearly on the concentration of TMQ in micelles. The rate constant for the reaction of the transient radical cation with TMQ was determined (200 L mol⁻¹ s⁻¹). At pH>13, the decay rate constant in micelar solutions is lower than that in aqueous solutions (negative micellar catalysis). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 703–708, April, 1997.     

A silver-catalyzed domino route toward 1,2-dihydroquinoline derivatives from simple anilines and alkynes

[reaction: see text] A silver-catalyzed domino reaction of simple anilines and alkynes generates 1,2-dihydroquinoline derivatives efficiently.     

Photolysis of 6-ethoxy-2,2,4-trimethyl-8-nitro-1,2-dihydroquinoline. Unusual dependence on the irradiation wavelength

The spectral and kinetic parameters of transient species generated in the irradiation of 6-ethoxy-2,2,4-trimethyl-8-nitro-1,2-dihydroquinoline were examined by stationary and pulse photolysis in the solvents: heptane, acetonitrile, methanol, and ethanol. Upon excitation of the long-wavelength absorption band (λ_ex > 450 nm), a reversible photochemical reaction was revealed, and the spectral and kinetic parameters of three transient species observed in the photolysis were characterized (λ_max = 390, 400, and 420 nm (acetonitrile), k = 97, 500, and 2000 s⁻¹, respectively). The absorption spectra and the rate constants of the decay of transient species are almost independent of the medium polarity and the presence of oxygen in the system. The excited state generated during irradiation to the short-wavelength absorption band (290 < λ_ex < 350 nm) is inactive in the photochemical reaction and deactivates without the formation of transient species. The mechanism of the reversible photochemical reaction is suggested, which involves the opening of the heterocycle N-C bond upon photoexcitation of the long-wavelength absorption band and the thermal back reaction.     

Effect of the solvent composition in methanol-pentane and methanol-acetonitrile mixtures on the quantum yield of proton transfer and reactions of transient species in the photolysis of 2,2,4,6-tetramethyl-1,2-dihydroquinoline

The photolysis of 2,2,4,6-tetramethyl-1,2-dihydroquinoline in binary MeOH-C₅H₁₂ and MeOH-MeCN mixtures was studied in dependence on the solvent composition by steady state and pulse photolysis. The photoinduced proton transfer from the N-H bond to the C(3) carbon atom of the heterocycle does not occur up to the methanol concentration of 0.25 (1 vol %) and 2.5 mol l⁻¹ (10 vol %) in the MeOH-C₅H₁₂ and MeOH-MeCN mixtures, respectively. The trends in the increase in the relative quantum yield of the proton transfer reaction (Q _mix/Q _MeOH) and the decay rate constant for 2,2,4,6-tetramethyl-2,3-dihydroquinoline, the product of the proton transfer reaction, in dependence on the composition differ significantly for these binary mixtures. The results are interpreted in terms of peculiarities in the aggregation of methanol and the distribution of the DHQ molecules and transient species in the mixtures.     

Photolysis and Cycloaddition Reactivity of Diferrocenyl Substituted Cyclopentadienone

The photolysis results of new diferrocenyl substituted cyclopentadienone(3) show that sunlight and air play an important role in the decomposition of compound 3, and two new compounds, 2-cyclopentenone(4) and α-pyrone(5), were obtained via photolysis of compound 3. The photolysis process was investigated by ¹H NMR, and a plausible mechanism for the formation of compound 5 was deduced. The cycloaddition reactions of substituted cyclopentadienones(3, 7, 9) with maleimide gave substituted imides 8, 10, 11, 12 and an unprecedented diferrocenyl substituted 1H-pyrrol-3(2H)-one derivative 13, respectively. The structures of compounds 4, 5, 8, 10, 11, 12 and 13 were confirmed by X-ray single crystal diffraction analysis technique.     

Photolysis of 1,2-anthraquinone diazide in aromatic hydrocarbons

It has been determined that the main products of photolysis of 1,2-anthraquinone diazide in benzene, toluene, anisole, nitrobenzene, and pyridine are the corresponding 1-hydroxy-2-arylanthraquinones that form as a mixture ofortho, meta, andpara isomers with significant content of themeta isomer (40–55%).Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk 630090. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 1000–1003, April, 1992.     

Dynamics of carbocation formation in the photolysis of 1,2,2,3-tetramethyl-1,2-dihydroquinoline in alcohols

Dynamics of the formation of the carbocation in the ground state as a result of photoinduced proton transfer from a solvent to the excited state of 1,2,2,3-tetramethyl-1,2-dihydroquinoline (3MDHQ) in MeOH and 2,2,2-trifluoroethanol (TFE) was registered by pump-probe laser photolysis (λ_pump = 310 nm) with femtosecond time resolution. The lifetimes of the excited singlet state of 3MDHQ τ = 115 and 780 ps were determined in TFE and MeOH, respectively. The transient species with absorption spectrum corre-sponding to the spectrum of the carbocation from 3MDHQ (λ_max = 480 nm) is generated at time delays lower than 500 fs from the unrelaxed excited singlet state.     

Photolysis of diazocyclopentadiene : Reactivity of cyclopentadienylidene in sulfides and ethers

Photolysis of diazocyclopentadiene in the presence of dimethyl, diethyl and tetramethylene sulfides gave the corresponding sulfonium cyclopentadienylide. But the ylides from diisopropyl and di-t-butyl sulfides were unstable, and the reaction mixture gave the CH and CS insertion products of cyclopentadienylidene and olefin elimination products. Reaction of diazocyclopentadiene in ethers gave the CH insertion and some CO insertion products. For diethyl ether, the insertion ratio into secondary and primary CH bonds was 19:1. For tetrahydrofuran, both α and β-CH insertion products were observed in ratio of 3:0. Photolysis of diazocyclopentadiene in allylic ethers gave the addition product of the carbene to the double bond, but in allylic sulfides gave both CS insertion and addition products of the carbene.     

Photolysis of cis-1,2-dihydroxyindane carbonate and cw-1,2-dihydroxy-1,2,3,4-tetrahydronaphthalene carbonate

Cyclic carbonate esters 2 and 3 were prepared and the photochemistry studied. The direct irradiation of these esters produces 1,3-diradicals which undergo either ring closure to form epoxides, H migration to form ketones or Grob type fragmentation processes which lead to products via ring expansion or contraction.     

The Reactivity of Diphenyl Carbonyl Oxide in Reactions with Alcohols

The reactivities of ten alcohols in the reactions with diphenyl carbonyl oxide Ph₂COO is characterized by the ratio k ^OH ₃₃ /k ₃₁, where k ^OH ₃₃ and k ₃₁are the rate constants of Ph₂COO reactions with an alcohol and diphenyldiazomethane PH₂CN₂, respectively. The values of k ^OH ₃₃ /k ₃₁range between 0.6 × 10^–2for MeOH to 6.0 for iso-PrOH at 70°C in acetonitrile. The donation of electron density to the alcohol hydroxyl group favors the attack of Ph₂COO; that is, Ph₂COO reacts as an electrophile.     

Supernucleophilic Reactivity of Hypobromite Ion toward 4-Nitrophenyl Diethylphosphonate in Water and Micelles of Cetyltrimethylammonium Bromide

The nucleophilic reactivity of the typical -nucleophile hypobromite ion, generated by the organic complexes of the tribromide ion, toward 4-nitrophenyl diethylphosphonate in water and micelles of cetyltrimethylammonium bromide (CTAB) was studied. The BrO^––CTAB system is one of the most effective for the decomposition of organophosphorus compounds; the concentrating effect of the reagents secures the rapid break down of 4-nitrophenyl diethylphosphonate in an aqueous–micellar medium with t _1/2 20 s (in water t _1/2 600 s).Yu. S. Simanenko: Deceased     

Primary Photophysical and Photochemical Processes in the Photolysis of 1,2-Dihydroquinolines in Different Solvents

The fluorescence lifetimes (τ_fl) of alkyl and alkoxy substituted dihydroquinolines (DHQ) were measured in hexane, isopropanol, methanol, and water. It was shown that τ_fl was determined by the solvent nature and weakly depended on substituents on the DHQ aromatic ring and heterocycle, with τ_fl being substantially lower in methanol than in the other solvents. The decrease in τ_fl in MeOH is caused by an increase in the rate constants of the photochemical reaction and nonradiative transitions in this solvent. The quantum yield of fluorescence in H₂O and MeOH, in which the photoinduced addition of the solvent molecules occurs, decreases with a decrease in the excitation wavelength within the limits of long-wavelength absorption band, thus providing strong evidence that the photochemical reaction proceeds from the unrelaxed excited state.     

Photolysis of 1,2-dihydroquinolines in micellar solutions of anionic and cationic surfactants

The kinetics of the photolysis of substituted 1,2-dihydroquinolines (DHQ) in micellar solutions was studied by steady-state and flash photolysis. The photolysis mechanism depends dramatically on the location of DHQ molecules in micelles, which is governed by the surfactant nature. In micellar solutions of the anionic surfactant sodium dodecyl sulfate (SDS), where the DHQ molecules are located in the Stern layer, the intermediate species decay kinetics follows a first-order law. When DHQ is in neutral form (pH 4–12), the rate constant of the intermediate carbocation decay increases from 25 to 198 s^?1 with an increasing concentration of DHQ in micelles. The positive micellar catalysis is caused by the acceleration of the final product formation with the DHQ molecule via proton abstraction from the intermediate cation. The formation of several types of intermediate species—carbocations in the aqueous phase and aminyl radicals in micelles—is observed in micellar solutions of the cationic surfactant cetyltrimethylammonium bromide (CTAB) due to the preferential location of DHQ molecules in the micellar core. The carbocation decays via a pseudofirst-order reaction with a rate constant close to that in the aqueous solution. The lifetime of the DHQ aminyl radicals in the micellar solutions is longer by several orders of magnitude than the lifetime observed for homogeneous solutions of hydrocarbons and alcohols.     

N-alkylation of 2,2,4-trimethyl-1,2-dihydroquinoline and its dimeric analogs under interphase-catalysis conditions

The possibility of the use of interphase catalysis for the synthesis of N-alkyl derivatives of 2,2,4-trimethyl-1,2-dihydroquinoline and its dimeric analogs was demonstrated. The effect of the nature of the alkylating agents on the reaction time and the yield of alkylation products was examined.Translated from Khimiya Geterotsikli-cheskikh Soedinenii, No. 8, pp. 1091–1093, August, 1988.     

Convenient synthesis of fluorinated quinoline, 1,2-dihydroquinoline, and 1,2,3,4-tetrahydroquinoline derivatives

A convenient synthetic method for 2-polyfluoroalkylated quinoline systems through the efficient generation of perfluoroalkylated imine from o-vinylanilines with perfluorinated hemiacetals or aldehyde hydrates was developed. In most cases, the major products are 2-polyfluoroalkyl-1,2-dihydroquinoline derivatives 3, which can be converted to either quinolines or 1,2,3,4-tetrahydroquinolines.     

Efficient construction of 1,2-dihydroquinoline and 1,2,3,4-tetrahydroquinoline rings using tandem Michael-aldol reaction

1,2-Dihydroquinolines and a 1,2,3,4-tetrahydroquinoline were efficiently constructed using tandem Michael-aldol reaction starting from N-protected o-aminobenzaldehydes and α,β-unsaturated carbonyl compounds in good yield.