Photoinduced oxygenation of tryptamines by aromatic amine N-oxides

Irradiation (1) (253-7 nm) of N_a,N_b-dimethyltryptaimne with pyridine N-oxide or benzo[c]cinnoline N-oxide in CH₂Cl₂ yielded 1,8-dimethyl-3a-hydroxy-1,2,3,3a,8-8a,- hexahydropyrrolo[2,3-b]indole (19), while with visible light N_b-(4-cyanobutadienyl)-N_a,N_b,- dimethyltryptamine (21) was obtained. This method was applied to trimethyltryptamine and the corresponding oxindole (34) and the N-formyl derivative (20) were obtained.     

Electronic structures of aromatic amine N-oxides

The electronic structures of heterocyclic amine N-oxides, nitrones, and nitrile N-oxides were systematically studied by the Pariser-Parr-Pople method. In addition, the intensity of n- ^* transition pertinent to conjugated N-oxide systems has been calculated. The results of these calculations were compared with the experimental ones reported hitherto and also carried out in the present work. The electronic structure and spectra of aromatic amine N-oxides were thus discussed in detail.

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Zusammenfassung Die elektronische Struktur heterozyklischer Amin-N-Oxide, Nitrone und Nitril-N-Oxide wird systematisch mit Hilfe der Pariser-Parr-Pople-Methode untersucht. Au\erdem wurde die IntensitÄt von n- ^*-übergÄngen konjugierter N-Oxide berechnet. Die Resultate wurden mit bekannten sowie eigenen experimentellen Ergebnissen verglichen. Die Elektronenstruktur und die Spektren aromatischer Amin-N-Oxide wurden so im Detail diskutiert.

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Résumé La structure électronique d'amine N-oxydes, de nitrones, et de nitrile N-oxydes ont été étudiés systématiquement par la méthode de Pariser-Parr-Pople. De plus, l'intensité de la transition n- ^* des systémes N-oxydes conjugués a été calculée. Les résultats de ces calculs ont été comparés aux résultats expérimentaux rapportés précédemment et également à ceux du présent travail. La structure électronique et le spectre des N-oxydes d'amines aromatiques ont ainsi été discutés en détail.

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Presented at the 21st (Osaka, April 1968) Annual Meeting of the Chemical Society of Japan, and the Symposium of Structure Chemistry and the Electronic State of Molecules (Tokyo, October 1968).     

A study on the transition state in the photooxygenations by aromatic amine N-oxides

Oxygen—atom transfer process in the photolysis of aromatic amine N-oxides was suggested to involve the primary oxygen—atom elimination from N-oxides to give “oxene” follwed by its reactions with the oxygen-acceptors.     

Reduction of amine N-oxides by diboron reagents

Facile reduction of alkylamino-, anilino-, and pyridyl-N-oxides can be achieved via the use of diboron reagents, predominantly bis(pinacolato)- and in some cases bis(catecholato)diboron [(pinB)(2) and (catB)(2), respectively]. Reductions occur upon simply mixing the amine N-oxide and the diboron reagent in a suitable solvent, at a suitable temperature. Extremely fast reductions of alkylamino- and anilino-N-oxides occur, whereas pyridyl-N-oxides undergo slower reduction. The reaction is tolerant of a variety of functionalities such as hydroxyl, thiol, and cyano groups, as well as halogens. Notably, a sensitive nucleoside N-oxide has also been reduced efficiently. The different rates with which alkylamino- and pyridyl-N-oxides are reduced has been used to perform stepwise reduction of the N,N'-dioxide of (S)-(-)-nicotine. Because it was observed that (pinB)(2) was unaffected by the water of hydration in amine oxides, the feasibility of using water as solvent was evaluated. These reactions also proceeded exceptionally well, giving high product yields. In constrast to the reactions with (pinB)(2), triethylborane reduced alkylamino-N-oxides, but pyridine N-oxide did not undergo efficient reduction even at elevated temperature. Finally, the mechanism of the reductive process by (pinB)(2) has been probed by (1)H and (11)B NMR.     

Wilkinson's catalyst catalyzed selective hydrogenation of olefin in the presence of an aromatic nitro function: a remarkable solvent effect

Optimal conditions for chlorotris(triphenylphosphine)rhodium(I) (Wilkinson's catalyst) catalyzed selective saturation of a double bond in the presence of a nitro function are developed. Aryl iodide and benzyl ether are also tolerated under these hydrogenation conditions.     

Photochemical hydroxylation of salicylic acid by hydrogen peroxide. Photocatalytic effect of Fe(III)

The rate and quantum yields of photoinitiated hydroxylation of salicylic acid by hydrogen peroxide can be increased substantially by adding Fe(III) compounds to the reaction mixture. The UV radiation reduces the catalytically inactive Fe(III) to catalytically active Fe(II) during the reaction, thereby continuously producing the Fenton reagent.

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Fe(III) . Fe(III) Fe(II) , .

     

Propargylamine synthesis by copper-catalyzed oxidative coupling of alkynes and tertiary amine N-oxides

An efficient method for synthesizing N,N-dimethylpropargylamines is described. The synthesis exploited the Cu(II)-catalyzed oxidative alkynylation reaction of trimethylamine N-oxides with alkynes in the absence of external oxidant. Both aromatic and aliphatic alkynes were utilized to achieve the corresponding products in moderate to excellent yields. The reaction conditions tolerated ester, hydroxy, and aldehyde groups.     

Pd(0)-catalyzed iodoalkynation of norbornene scaffolds: the remarkable solvent effect on reaction pathway

A palladium-catalyzed iodoalkynation of norbornene has been realized with the use of alkynyl iodides 1, which is found to be strongly solvent-dependent. MeCN favors 1,7-iodoalkylation product 3 while CCl(4) leads to 1,2-iodoalkylation product 4.     

Regioselective hydroxylation of diverse flavonoids by an aromatic peroxygenase

Aromatic peroxygenases are extracellular fungal biocatalysts that selectively oxidize a variety of organic compounds. We found that the peroxygenase of the fungus Agrocybe aegerita (AaeAPO) catalyzes the H₂O₂-dependent hydroxylation of diverse flavonoids. The reactions proceeded rapidly and regioselectively yielding preferentially monohydroxylated products, e.g., from flavanone, apigenin, luteolin, flavone as well as daidzein, quercetin, kaempferol, and genistein. In addition to hydroxylation, O-demethylation of fully methoxylated tangeretin was catalyzed by AaeAPO. The enzyme was merely lacking activity on the quercetin glycoside rutin, maybe due to sterical hindrance by the bulky sugar substituents. Mechanistic studies indicated the presence of epoxide intermediates during hydroxylation and incorporation of H₂O₂-derived oxygen into the reaction products. Our results raise the possibility that fungal peroxygenases may be useful for versatile, cost-effective, and scalable syntheses of flavonoid metabolites.     

Studies on tertiary amine oxides. LXVII . Reactions of aromatic N-oxides with 3-arylrhodanines in the presence of acetic anhydride

Quinoline 1-oxides 1 readily react with 3-arylrhodanines 2 in the presence of acetic anhydride to afford 3-aryl-5-(2-quinolyl)rhodanines 3 in high yields. These products resist hydrolysis under both alkaline and acidic conditions, but is oxidized to quinaldinic acid 1-oxide 4 with 30% hydrogen peroxide in hot acetic acid. Besides isoquinoline 2-oxide 5 , pyridine 1-oxide 7a also reacts in the same way to give 3-aryl-5-(2-pyridyl)rhodanines 8 , although the reactivity of γ-picoline 1-oxide 7b is considerably lower. Contrary to 3 , 3-phenyl-5-(2-pyridyl)rhodanine 8a is successfully hydrolyzed with boiling 48% hydrobromic acid to 2-pyridinemethanethiol 10 in 57% yield.     

Cytochrome P-450 model compound catalyzed selective hydroxylation of C-H bonds: dramatic solvent effect

Selective hydroxylation of cyclohexane and cyclohexene by t-BuOOH in presence of F2oTPPFe(III)Cl as the catalyst has been achieved at room temparature in high yields.     

A remarkable solvent effect toward the Pd/C-catalyzed cleavage of silyl ethers

Selective hydrogenation conditions of olefin, benzyl ether and acetylene functionalities in the presence of TBDMS or TES ether have been developed.     

Marked effect of aromatic solvent on unfolding rate of helical ethynylhelicene oligomer

Optically active acyclic ethynylhelicene oligomers were synthesized in high yields by a two-directional method involving Sonogashira coupling and deprotection. Their CD spectra in chloroform exhibited large differences between the oligomers with less than seven helicenes and their higher homologues, which indicated the formation of helical structures for the latter and random coil structures for the former. The helical heptamer gradually unfolded to a random coil structure in chloroform at room temperature. The unfolding rate was examined by CD in several aromatic solvents as well, and the rate constant k was found to be highly dependent on the type of aromatic substituent: k differed by seven orders of magnitude between iodobenzene and trifluoromethylbenzene. Several features of the rates are notable: The reaction rates in halobenzenes were in the order of iodobenzene > bromobenzene > chlorobenzene > benzene > fluorobenzene > m-difluorobenzene, those in alkylbenzenes were styrene > phenylacetylene > ethylbenzene > toluene > benzene, and those in heteroatom-substituted arenes were thioanisole > benzonitrile > anisole > ethyl benzoate > benzene > trifluoromethylbenzene. The log k values exhibited good correlation with the absolute hardness, eta, of the arenes, and higher unfolding rates were observed in the soft arenes. Vapor pressure osmometry studies indicated that the helical structure of the heptamer is dimeric in benzene, fluorobenzene, and trifluoromethylbenzene, while the random coil structure of the heptamer is monomeric in chloroform and toluene. When a chloroform solution of the random coil structure was concentrated to a small volume, the helical structure could be regenerated.     

The remarkable role of hydrogen bond,halogen, and solvent effect on self-healing supramolecular gel

Self-healing supramolecular gels of low-molecular-weight (LMW) molecules are smart soft materials; however, the development of self-healing LMW gelator is still a challenging task because of the lack of in-depth studies about self-healing mechanisms of LMW gels and the solvent effect on gel properties. Therefore, herein a different perspective was used to study a family of D-gluconic acetal-based gelators with variable structural fragments in 14 different solvents, and a more detailed understanding of self-assembly and self-healing mechanism of supramolecular gels was attained. Based on the critical gelation concentration, phase transition temperature, and rheological data, A8 bearing an amide group in side chain and two chlorine atoms linked to benzene ring was found to be an outstanding gelator, which could form gels with good self-healing ability in a variety of solvents. Interestingly, A8 gel formed in n-BuOH demonstrates high transparency, good mechanical strength, self-supporting behavior, and great self-healing ability from mechanical damage. Based on the Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and theoretical calculation analysis, the self-assembly and self-healing mechanisms of A8 gel were proposed, indicating that a combination of hydrogen bonding and halogen effect was responsible for the efficient self-healing behavior of supramolecular gel. Furthermore, the analysis of solvent parameters indicated that the dispersion force of solvent favored gelators to self-assemble, hydrogen bonding donor ability of solvent mainly affected the formation of one-dimensional assembly, and hydrogen bonding receptor ability and polarity of solvent mainly influenced the supramolecular interactions among assemblies, significantly intervening the self-healing ability of gels. Overall, this study provides a new perspective to the understanding of gelator structure–property correlation in solvents and sheds light for future development of self-healing supramolecular gels.     

Photocatalytic hydroxylation of aromatic ring by using water as an oxidant

Electrophilic oxygen species photocatalytically derived from water molecules can selectively react with the aromatic ring of both benzene and its derivatives to produce the corresponding phenols and hydrogen over platinum-loaded titanium oxide when illuminated with light of appropriate wavelength in the absence of oxygen.     

Influence of the amine structure on the polymerization of methyl methacrylate photoinitiated by aromatic ketone/amine

The polymerization of methyl methacrylate photoinitiated by 2‐chlorothioxanthone in the presence of amines of different structures has been investigated. The photoinitiation efficiency of these systems is highly dependent on the structure of the amine. The polymerization rate increases with the amine concentration, reaching a constant value in an amine concentration range of 10–30 mM. At these amine concentrations, aliphatic hydroxyalkyl amines are more efficient photoinitiators than the corresponding alkyl‐substituted compounds. Dimethylanilines with electron‐acceptor substituents in the 4‐position give higher polymerization rates than electron‐donor‐substituted anilines. The photophysics of these photoinitiation systems has been studied in the polymerization medium. These data show that the singlet and triplet excited states of thioxanthones are efficiently deactivated by the amine. Rate constants are well correlated to the oxidation potential of the amine. These studies have allowed us to simulate the dependence of the photoinitiation efficiency with the amine concentration and indicate that the active radicals are produced from the interaction of the ketone triplet with the amine. Also, photochemical studies have allowed us to establish that the dependence of the polymerization rate on structural features of amines is mainly due to differences in the fraction of produced active radicals that add to the monomer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2888–2893, 2002