Enthalpies of the Diels–Alder reactions of a series of dienes with tetracyanoethylene and 4-phenyl-1,2,4-triazoline-3,5-dione

Russian Chemical Bulletin - The enthalpies of the Diels–Alder reactions of twenty dienes with two active dienophiles, tetracyanoethylene and 4-phenyl-1,2,4-triazoline-3,5-dione, are compared,...     

The reaction of oximes with 4-phenyl-1,2,4-triazoline-3,5-dione to produce nitric oxide – Model compounds for nitric oxide synthase

Certain oximes form nitric oxide upon reaction with 4-phenyl-1,2,4-triazole-3,5-dione (PTAD). The oximes appear to undergo an Alder-ene reaction with the PTAD enophile to form a nitroso intermediate capable of dimerization and/or nitric oxide formation. Upon exposure to oxygen, the nitroso compounds eventually form ketones. This reaction may serve as a model for the study of nitric oxide synthase (NOS), the enzyme responsible for physiological production of nitric oxide. NOS is known to produce an oxime intermediate which reacts with oxygen to produce nitric oxide and citrulline.     

Stereochemistry of the coupling step in photo-S_(RN) 1 reaction

The photo-S_(RN) 1 reaction of (+)-camphor and aryl halides was investigated in order toestimate the stereochemistry of the coupling step of aryl radicals with a nucleophile. The ratio of endo toexo products determined by ~1H NMR and CD spectra was found to be 99:1. MNDO calculationsof the orbital parameters showed a favorable one-sided overlap of the enolate ion with the SOMO of arylradical. In addition, fragmentation of (ArX)~- was found to be related to the energy of SOMO of(ArX)~-.     

2,2′-carbonyl-bis(3,5-dioxo-4-methyl-1,2,4-oxadiazolidine): II-reagent for the direct esterification of carboxylic acids.

Reaction of carboxylic acids including N-protected α-amino acids with 2,2′-carbonyl bis(3,5-dioxo-4-methyl-1,2,4-oxadiazolidine) and alcohols affords the corresponding esters under mild conditions.     

Diastereo-controlled Diels–Alder cycloadditions of erythrose benzylidene-acetal 1,3-butadienes by 4-substituted-1,2,4-triazoline-3,5-dione: Evidence for the stereoelectronic effects on the dienes

Erythrose benzylidene-acetal 1,3-butadienes are studied as partners in Diels–Alder cycloadditions. A high diastereofacial improvement is found in cases where both the alcohol function is protected and a π–π interaction between the diene and dienophile is possible. Several competing factors have been studied independently in order to explain its influence on the selectivity of the cycloadditions.     

An open chain product in the reaction of benzil with thiocarbohydrazide

An open chain compound was obtained by reaction of benzil with thiocarbohy-drazide in acidic condition. Its derivative, namely, benzil bis-(5-isopropylidene-3-thiocarbohydrazone) has been structurally characterized by X-ray single crystal diffraction method. Crystallographic data: C22H26N8S2, Mr=466.62, monoclinic, space group C2/c, a=12.215(3), b=11.473(2), c=17.032 (3)A, B=98.96(2)0, V=2357.7(9)A3, Z=4, Dc=1.32 g/cm3, F(000)=1040, u(Mo Ka)=2.43 cm-1. Final R=0.050, Rw=0.061 for 1103 unique and observed reflections with I> 3o(I). The effect of the structures on the formation of the open-chain intermediates during the cyclization of (2:2) Schiff base macrocyclic compound has been discussed and a possible mechanism for the ring closure has been suggested.     

2,2′-carbonyl-bis(3,5-dioxo-4-methyl-1,2,4-oxadiazolidine): I-A new reagent for the preparation of carbamates and amides,application to the synthesis of dipeptides.

2,2′-Carbonyl bis(3,5-dioxo-4-methyl-1,2,4-oxadiazolidine) was prepared and used for the synthesis of various carbamates and dipeptides.     

Structure of intermediates in the Hantzsch reaction of phenylchloropyruvic acid derivatives with N,N′-diphenylthiourea

The intermediates in the Hantzsch reaction of the methyl ester and diethylamide of phenylchloropyruvic acid with N,N-diphenylthiourea are derivatives of 2-phenylimino-3,5-diphenyl-4-hydroxythiazoline-4-carboxylic acid. They exist as an equilibrium mixture of two diastereomers in solution.A. E. Arbuzov Institute of Organic and Physical Chemistry of the Kazan Scientific Center, Russian Academy of Sciences, Kazan' 420088; Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 975–980, July, 1999.     

Kinetics and mechanism of the reaction of benzoyl chloride with 4-(4′-N,N-dimethylaminostyryl)pyridine-N-oxide in toluene

The reaction of benzoyl chloride with 4-(4-N,N-dimethylaminostyryl)pyridine-N-oxide in toluene proceeds according to an addition—elimination mechanism. The rate and equilibrium constants of the individual steps were determined. An inhibiting effect of the substrate was detected.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 5, pp. 316–318, September–October, 1995.     

Electroanalytical studies of the corrosion-protection properties of 4-amino-4H-1,2,4-triazole-3,5-dimethanol (ATD) on mild steel in 0.5?N sulfuric acid

Inhibition of the corrosion of mild steel in aerated 0.5?N H₂SO₄ solution by 4-amino-4H-1,2,4-triazole-3,5-dimethanol (ATD) was investigated by use of potentiodynamic polarization (Tafel), electrochemical impedance spectroscopy, adsorption, and surface morphological studies. The effects on the rate of corrosion of inhibitor concentration, temperature, extent of surface coverage, adsorption kinetics, and surface morphology were investigated. Inhibition efficiency increased markedly with increasing ATD concentration and decreased slightly with increasing temperature. The presence of ATD reduced the capacitance of the double layer and increased the charge-transfer resistance. Values of the activation energy (E _a) and of the thermodynamic data adsorption equilibrium constant (K _ads) and free energy of adsorption (??G _ads) were computed from the temperature dependence of the corrosion current. The inhibitor molecule first became adsorbed on the mild steel surface, obeying the Langmuir adsorption isotherm, and substantially reduced the rate of corrosion. Results of electroanalytical studies revealed that ATD acts as a mixed-type inhibitor.     

Synthesis and crystal structure of 2′-(3,5-dioxo-1,2,4-triazinane-1-yl)acetic acid and the product of its reaction with copper(II) chloride

A new organic compound, 2-(3,5-dioxo-1,2,4-triazinane-1-yl)acetic acid, was prepared by transit template synthesis, and its crystal structure was determined. The ability of this compound to form stable metal complexes, where it acts as an N,O-chelating ligand, was demonstrated using its Cu(II) compound as an example.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 3, 2005, pp. 187–194.Original Russian Text Copyright © 2005 by Filippova, Bologa, Simonov, Gdaniec, Gerbaleu.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

Solvent-free reaction of 1,2,4-triazine-5-carbonitriles with 4-(cyclohex-1-en-1-yl)morpholine. Unexpected decyanation in addition to classical aza-Diels–Alder reaction

The reaction of 1,2,4-triazine-5-carbonitriles with 4-(cyclohex-1-en-1-yl)morpholine under solventfree conditions has been found to follow two pathways: aza-Diels–Alder reaction and unexpected decyanation of the initial nitriles. The scope of the revealed decyanation reaction has been roughly estimated.     

The stereochemistry of the Grignard — Ortho ester reaction revisited: Regioselective endocyclic cleavage in the reaction of Grignard reagents with cis-2-methoxy-4-methyl-1,3-dioxane

The reaction of cis-2-methoxy-4-methyl-1,3-dioxane (4) with Grignard reagents proceeds in a totally regioselective manner via rupture of the less congested C(2)O(1) bond remote from the 4-methyl substituent. The analogous r-2-methoxy-cis-4,cis-6-dimethyl-1,3-dioxane (2) is totally inert to the action of Grignard reagents.     

Autoassembly of cage structures. 4. Stereochemistry of 2,5-di-tert-butyl-γ-butyrolactone-4-carboxy-s-(α)-phenylethylamide

The diastereoisomeric lactonamides (2a, b), obtained from the dilactone (1) and S-phenylethylamine, have been separated. X-ray crystallography shows that the high-melting isomer (2a) has theR-configuration at the chiral centers C² and C⁴, the enantiomeric conformation of the -lactone ring being of theS-type in thetwist form, intermediate between envelope ² E and semi-chair ₃ ² T. It is shown by molecular mechanics that the minimum steric energy of2a corresponds to a conformation of the heterocycle close to the envelope form₃E. Examination of van der Waals interactions shows that the calculated structure for2a is preferred. The reasons for the nonidentity of the forms of the -lactone ring of2a in the crystal and the free state are discussed. The crystal structure of2a is composed of two geometrically similar independent molecules associated along the axis by weak hydrogen bonds of two types, the energies of which have been estimated from the v_XH values, which are related by the expression v_XH=f(R_X...O), where X=N, O.For previous communication, see [1].N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 7, pp. 1601–1611, July, 1992.     

Chemical effects of the (n, γ) reaction in alkali selenates

Thermal annealing isochronals have been measured for sodium and potassium selenates. They are quite dissimilar. The isochronal for a dehydrated sample of irradiated sodium selenate hydrate suggests that dehydration removes the more readily annealable fragment centres.The temperature dependence of the radiation annealing of the same two salts has also been explored. An explanation of this temperature dependence, which also accounts for various features of the isothermal radiation annealing process, is proposed.     

Six lanthanide(III) coordination polymers with 3,5-bis(4′-carboxy-phenyl)-1,2,4-triazole: syntheses,structures, and photoluminescence

Six 3-D lanthanide(III)-metal-organic frameworks (MOFs) through multidentate 3,5-bis(4′-carboxy-phenyl)-1,2,4-triazole (H₂BCPT); acetic acid (HOAc); and corresponding trivalent rare earth chloride, {[Ln(BCPT)(OAc)(H₂O)]·(H₂O)}_n (Ln = Nd³⁺ (1); Sm³⁺ (2), Gd³⁺ (3), Tb³⁺ (4), Ho³⁺ (5), Yb³⁺ (6)), have been synthesized. MOFs 1–6 were characterized via FT-IR spectroscopy, elemental analysis, X-ray single-crystal diffraction, thermal analysis, and fluorescence. MOFs 1–6 are isomorphous, which can be described as a 3-D construction containing a dinuclear cluster [Tb₂(CO₂)₂(O)₂]. The 3-D structure with (4,4) topologies have been extended through BCPT^2? using μ₄-kO;kO;kO;kO coordination modes. Solid-state luminescence of 1–4 and 6 shows the characteristic bands of Nd³⁺, Sm³⁺, Tb³⁺, and Yb³⁺ from visible to near-infrared spectral regions.     

Unexpected reduction of the nitro group in (3-nitrophenyl)-1,2,4-triazines during their aza-Diels–Alder reaction with 1-morpholinocyclopentene

Unexpected reduction of the nitro group to the amino one during aza-Diels–Alder reaction between (3-nitrophenyl)-1,2,4-triazines and 1-morpholinocyclopentene (neat, 200 °C, argon) occurred to furnish 4-(3-aminophenyl)-6,7-dihydro-5H-cyclopenta[c]pyridines.