Electronic spectra and structure of 2,4-dihalopicolines and their N-oxides

UV spectra of 2,4-dihalopicolines and their N-oxides are presented, and the influence of substituents on spectral parameters is discussed. The electronic spectra were calculated by a modified INDO method. Transition energies, intensities, and assignments were compared with UV spectra. The degree of intramolecular charge transfer in 2,4-dihalopicolines is greater than in 2-halopicoline N-oxides and smaller than in 2-halo-4-nitropicoline N-oxides. Difference values of HOMO-LUMO energies point out that the susceptibility on photochemical reaction lies in the order: 2-halo-4-nitropicoline N-oxides > 2,4-dihalopicoline N-oxides > 2-halopicoline N-oxides > pyridine N-oxide. Department of Organic Chemistry, University of Economics, PL-53-342 Wroclaw, Poland. Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 34, No. 10, pp. 1352–1366, October, 1999.     

Identification of the aromatic tertiary N-oxide functionality in protonated analytes via ion/molecule reactions in mass spectrometers

A mass spectrometric method is presented for the rapid identification of compounds that contain the aromatic N-oxide functional group. This method utilizes a gas-phase ion/molecule reaction with 2-methoxypropene that yields a stable adduct for protonated aromatic tertiary N-oxides (and with one protonated nitrone) in different mass spectrometers. A variety of protonated analytes with O- or N-containing functional groups were examined to probe the selectivity of the reaction. Besides protonated aromatic tertiary N-oxides and one nitrone, only three protonated amines were found to form a stable adduct but very slowly. All the other protonated analytes, including aliphatic tertiary N-oxides, primary N-oxides, and secondary N-oxides, are unreactive toward or react predominantly by proton transfer with 2-methoxypropene.     

Ionisation Energies and the Electronic Structures of the N-oxides of diazabenzenes

The ionisation energies and the HeI photoelectron spectra of the N-oxides of diazabenzenes are presented. The valence electronic structures of the N-oxides are discussed in view of the ionisation energies, and the profiles, of the bands. The interpreted data are compared to calculations which are in good agreement. The results are correlated to the physicochemical studies, and particularly to the electronic absorption spectroscopy, of the N-oxides. The assignment of the photoelectron spectra of the azabenzenes are considered with reference to the spectra of their N-oxides.     

Acid-base equilibria of substituted pyridine N-oxides in methanol

Acid dissociation constants in methanol for eight substituted pyridine N-oxides having a wide range of acid-base properties, [quinoline N-oxide (bi-cyclic amine N-oxide) and pyridine (heterocyclic amine)] have been determined using the potentiometric titration method. A linear correlation between ourmethanol data and aqueous pK _a values from the literature has been found. As in polar aprotic solvents cationic homoconjugation phenomenon has been found to be present for sufficiently basic N-oxides. The tendency of substituted pyridine N-oxides towards cationic homoconjugation in methanol is weaker than in polar aprotic solvents and increases with increasing basicity of N-oxides. It has also been found that, in contrast to polar aprotic solvents, the cationic homoconjugation phenomenon in methanol is much more pronounced for heterocyclic amines than their N-oxides.     

Chemical properties of N'-cyanodiazene N-oxides. Reactions involving the nitrile group

The reactivity of the nitrile group in N'-cyanodiazene N-oxides has been examined for the first time. A general approach to the synthesis of nitrogenous functional derivatives of azoxycarboxylic acids by reaction of N'-cyanodiazene N-oxides with nucleophiles (water, alcohol, and hydroxylamine) is described. A method of synthesis of novel azoxy-1,2,4-oxadiazoles and tetrazoles has been developed in which aliphatic, aromatic, or heterocyclic N'-cyanodiazene N-oxides are reacted with benzonitrile N-oxide or sodium azide. Trimerization of N-cyanodiazene N-oxides, catalyzed by anhydrous HCl, has given novel symm-triazines in which the heterocycle bears three diazene N-oxide groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1647–1653, July, 1991.     

Reactions between Grignard reagents and heterocyclic N-oxides: stereoselective synthesis of substituted pyridines, piperidines, and piperazines

In this perspective we discuss the recent developments of stereoselective synthesis of substituted pyridines, piperidines, and piperazines from cheap and commercially readily available starting materials. Pyridine N-oxides and pyrazine N-oxides are reacted with alkyl, aryl, alkynyl and vinyl Grignard reagents to give a diverse set of heterocycles in high yields. Optically active substituted piperazines are obtained by an asymmetric reaction from pyrazine N-oxides using sparteine as chiral ligand. In addition, a stereoselective synthesis of dienal-oximes from the reaction between pyridine N-oxides and Grignard reagents is presented, which results in a useful intermediate for the synthesis of a diverse set of compounds.     

Nitrogen-oxygen and oxygen-oxygen alkyl group migrations. synthesis of 1,2,4-triazine hydroxamic acid esters

Novel 1,2,4-triazine hydroxamic acid esters and alkylated 2, 3-dihydro-1,2,4-triazine N-oxides were prepared by rearrangement and selective alkylations of 3-alkoxy and 3-alkylamino-1,2,4-triazine N-oxides.     

Halogen Bonding Adsorbent Pyridine N-oxides for Iodine Capture in Water

Rapid capture of ¹²⁹I with high volatility and toxicity in the environment has attracted much attention. Herein we reported a firstly synthesized nonporous material: pyridine N-oxides (NTPO and ATPO) as iodine adsorbent. Both of NTPO and ATPO exhibit remarkable performance on the adsorption of iodine in aqueous solution, vapor state and organic solvents. Upon the capture of iodine, pyridine N-oxides were transformed to binary cocrystals combined with the pyridine N-oxides and iodine which is driven by halogen bond between iodine and oxygen atoms. Moreover, pyridine N-oxides shows high chemical, thermal and moisture stability.     

Facile one-pot direct arylation and alkylation of nitropyridine N-oxides with Grignard reagents

Facile arylation and alkylation of nitropyridine N-oxides were developed through the reactions of Grignard reagents with nitropyridine N-oxides. For the same 4-nitropyridine N-oxide, arylation occurred at the 2- (or 6-) position, whereas alkylation occurred at the 3-position in an adjustably site-selective manner. The cooperative action of the two groups was discovered in the reactions of 3-nitropyridine N-oxides. This protocol can find wide applications in building various pyridine compounds as illustrated in total syntheses of Emoxipin and Caerulomycin A and E.     

Synthesis of 4-nitroisoxazoline N-oxides

The reaction of some aliphatic diazo compounds with trans-1-phenyl-1,2-dinitroethylene gave the first representatives of 4-nitroisoxazoline N-oxides, which differ from the unknown 3-nitroisoxazoline N-oxides with respect to their individual physical and chemical properties.     

Novel π-conjugated structures with fluorescent properties based on 4-alkoxytetrahydroquinazoline N-oxide

Russian Chemical Bulletin - Synthetic approaches to previously unknown 4-OR-2-methyltetrahydroquinazoline N-oxides were elaborated. 4-Alkoxy- and 4-aryloxy-2-methyltetrahydroquinazoline N-oxides...     

N-oxides of 2- and 4-azafluorenones and nitro derivatives of 2- and 4-azafluorenes

It was demonstrated by PMR spectroscopy that mixtures of N-oxides of 6- and 7-nitro derivatives are formed in the nitration of the N-oxides of 3-methyl-2- and 4-azafluorenes. The products were deoxygenated to give nitro derivatives of 2- and 4-azafluorenes. The N-oxides of nitro-substituted azafluorenes were converted to salts of the aci forms by the action of alkali.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1396–1399, October, 1982.The authors thank K. F. Turchin for his assistance in recording the spectrum of nitration product VI at 200 MHz.     

Reaction of 2‐Phenyl‐4‐arylidene‐1,3‐oxazolones with Different Nucleophiles for Synthesis of Some New Heterocycles

Refluxing of 1,3‐oxazolone ( 1a ) with malononitrile in dry benzene and in the presence of ammonium acetate afforded imidazolone derivative ( 2 ). However, carrying out the same reaction in absolute ethanol and in the presence of piperidine as a base gave the benzamide derivative ( 4 ). Fusion of ( 1a ) with p‐anisidine gave the open adduct benzamide ( 6 ), which cyclized in acidic medium to give imidazolone derivative ( 7 ). Heating of imidazolone ( 7 ) with malononitrile above its melting point afforded 1,3‐diazepine derivative ( 8 ). Reaction of the carbohydrazide ( 9 ) with isatin in ethanol gives the corresponding Schiff base ( 11 ), which then reacted with acetyl acetone, ethyl acetoacetate, ethyl cyanoacetate, and malononitrile in n‐butanol and piperidine to afford benzamide derivative ( 13 , 14 , 15 ) and ( 16 ), respectively. The structures of the newly synthesized compounds were established on the basis of IR, ¹H‐NMR, mass spectra, and elemental analyses.     

In Process Citation

The polarographic behaviour of the acetyl- and benzoyl pyridine N-oxides shows the same type of anomalies as those which have previously been mentioned in the case of the corresponding formyl pyridine N-oxides: when the substituent lies in the 2 or 4 position, the N-oxide group and the carbonyl group are simultaneously reduced, the 3-isomers being normally reduced at all pH values. From the ultraviolet spectra, one concludes that the carbonyl group is hydrated, but not so strongly as in the case of the formyl pyridine N-oxides.     

Palladium-catalyzed C-H functionalization of pyridine N-oxides: highly selective alkenylation and direct arylation with unactivated arenes

Two catalytic protocols of the oxidative C-C bond formation have been developed on the basis of the C-H bond activation of pyridine N-oxides. Pd-catalyzed alkenylation of the N-oxides proceeds with excellent regio-, stereo-, and chemoselectivity, and the corresponding ortho-alkenylated N-oxide derivatives are obtained in good to excellent yields. Direct cross-coupling reaction of pyridine N-oxides with unactivated arene was also developed in the presence of Pd catalyst and Ag oxidant, which affords ortho-arylated pyridine N-oxide products with high site-selectivity.     

Synthesis of marine alkaloids leucettamines B and C by β-lactam ring rearrangement

A new method for the synthesis of marine alkaloids leucettamines B and C from Leucetta sp. sponges is described. The key step is the base-promoted rearrangement of β-lactam into imidazolone ring. Leucettamines B and C as well as their N-benzoyl derivatives were obtained in high yields. Single-crystal structures of both leucettamines B and C were determined by X-ray diffraction confirming Z-configuration of double bond at 4-position of imidazolone.     

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.     

New ditopic organic ligands with 2-pyridylbenzothiazole and 5-pyridylmethylidene-2-(methylthio)imidazolone fragments

Russian Chemical Bulletin - New ditopic organic ligands with (pyridylmethylidene)imidazolone and pyridylbenzothi-azole moieties were synthesized by Cu-catalyzed azide-alkyne cycloaddition of...