α,β-unsaturated oximes : Isoxazoline formation by thermal cyclisation of compounds related to benzalacetophenone oxime and isoxazoline thermal cycloreversion reactions

At about 300° the title compounds yield fragments attributed to cyclisation to isoxazolines and subsequent cycloreversion. Isoxazolines are formed at about 200° and can usually be isolated. At 300° they yield the same products as the oximes.Thus benzalacetophenone oxime gives 3,5-diphenylisoxazoline which then largely undergoes two distinct cycloreversions: (a) 1,3-cleavage (numbers refer to isoxazoline bonds) yielding benzonitrile and acetophenone and (b) reductive 1,4-cleavage yielding benzaldehyde and 1-phenylethylimine hydrolysis products. By-products are 2,4,6-triphenylpyridine, water and ammonium benzoate. With α-methylchalcone oxime reductive 1,4-cleavage is suppressed and with β-methylchalcone oxime both modes of cleavage are suppressed and 5-methyl-3,5-diphenylisoxazole is the stable product. An analogue of α-methylchalcone oxime, 2-methyl-1-phenyl-3-(2-thienyl)prop-2-ene-1-one oxime gives fragments attributed to both cleavage modes of an unisolatable and hitherto unknown isoxazoline.Possible mechanisms for the cyclisation and cycloreversions are discussed and the reductive 1,4-cleavage is believed to be a cycloreversion of a vinyl-nitrene.     

-(1-phenylhydrazino)-alkanone phenylhydrazones: The reaction with carbonyl compounds

The unsymmetrically disubstituted hydrazines 1 were condensed with carbonyl compounds. Some of the expected condensation products were isolated, but some were formed as unstable intermediates which underwent 1,4-elimination: The phenylhydrazone of the carbonyl compound used was obtained, together with the corresponding phenylazo-alkene 11 or alternatively, the 1,4-addition product of a different protic nucleophile to 11.     

-Fluoro decalones as chiral epoxidation catalysts: fluorine effect

Three rigid monofluorinated trans-decalones 4a, 5e, and 6e (90% ee) have been synthesized from commercially available (−)-(R)-methyl naphthalenone (90% ee). Their structures have been fully characterized (NMR, X-ray): ketones 4a and 5e are Me,F-disubstituted to the carbonyl with the fluorine axial and equatorial, respectively, while ketone 6e is F-monosubstituted to the carbonyl with the fluorine equatorial. The use of these ketones as chiral catalysts for the epoxidation of trans-olefins (such as stilbene, β-methylstyrene and p-methoxy cinnamate) through the formation of dioxiranes shows (i) that dioxiranes with an equatorial fluorine to the dioxirane ring are less reactive and provide lower ee’s than dioxiranes with an axial fluorine and having the same chirality and (ii) that an axial methyl to the dioxirane ring is significantly less efficient than a fluorine. The results corroborate Armstrong and Houk’s theoretical model and our first hypothesis to rationalize the inverted enantioselectivities observed using -fluorinated cyclohexanones having the same chirality, i.e.: rapid ring inversion (Curtin–Hammett principle) allows the dioxirane conformation to have the fluorine axial (even if less populated than the other) to contribute significantly to the epoxidation reaction.     

-mononitroalkyl derivatives of indium

Dealkylation of trialkylindium by -mononitroalkane leads to the formation of the previously unknown -nitroalkyl derivatives of indium. An investigation of the chemical properties and of the ¹¹⁵In nuclear quadrupole resonance spectra of these compounds has been undertaken. An analysis of the data obtained from these investigations suggests the existence of intramolecular O→In coordination in the -nitroalkyl derivatives of indium.     

,-Difluoroketone inhibitors of HMG CoA reductase

The rationale for a new class of HMG CoA reductase inhibitors, represented by ,ga-difluoroketones 3 and 4, is described. The syntheses of 3, 4, and their nonfluorinated analogue 5 are presented.     

-Halogenoketones—XIII Chromone epoxides; their synthesis and acid-catalysed rearrangement

The chromone epoxide ring system has been synthesised. Base-catalysed cyclization and dehydrobromination of -bromo-o-acyl (aroyl) oxyacetopheones or 2-bromo-1, 3-diones yielded 3-substituted chromone epoxides. Acid-catalysed rearrangement of a 2-methylchromone epoxide in an aprotic solvent gave a 2-methylenech-romanonol, while a 3-methoxymethylchromone epoxide fragmented to chromonol under these conditions; in alchols, chromone epoxides gave 2-alkoxychromanonols.     

-Halogenoketones—XIV Studies in the chemistry of 2'-hydroxyacrylophenones

An initial study of the side-chain unsubstituted 2'-hydroxyacrylophenone system shows it to have a considerably greater propensity for intermolecular addition than the comparable 2'-hydroxychalcone system, readily undergoing base-catalysed addition of, for example, alcohol and thereby diverting typical chalcone reactions requiring alcoholic alkali. 2'-Acetoxyacrylophenone dibromides and bromoalkoxides cyclize with base to chromone epoxides as do 2'-acetoxy--bromoacrylophenones in alcoholic alkali.     

Study of two diastereomeric pairs of regiosomeric 2-isoxazolines by tandem mass spectrometry with electron impact ionization

On electron impact (EI) ionization, two cis/trans pairs of 4-methyl-5-phenyl and 4-phenyl-5-methyl regioisomeric 3-carbethoxy-2-isoxazolines showed normal mass spectra and mass-analysed ion kinetic energy (MIKE) spectra of metastable (MI) and collision-activated (CA) molecule ions, allowing unequivocal differentiation of the regioisomers. The cis/trans stereoisomers of each regioisomer showed very similar normal mass spectra. Very interestingly, the cis- and trans-4-phenyl-5-methyl stereoisomers appeared reasonably differentiated by the molecule ion MIKE spectra, whereas the 4-methyl-5-phenyl regioisomeric pair of stereoisomers did not. The influence of the phenyl substituent to the fragmentation processes was notable. Some fragments of interest were studied by comparison of their MIKE spectra with those of model ions, generated by EI from suitable substrates, including (i) the isomeric α,β-unsaturated oxime, namely ethyl (Z)-2-(hydroxymino)-3-methyl-4-phenylbut-3-enoate, a by-product of importance for the mechanism(s) of the addition/cycloaddition reactions of nitrile oxides to alkenes and (ii) trans-β-methylstyrene, a dipolarophilic reactant in the same reactions. The favoured heterocyclic C(5)–O(1) bond cleavage occurred only for the ionized 4-methyl-5-phenyl 2-isoxazoline pair, leading to a distonic ion of relevance, as it can represent either a reasonable precursor for both the isomerization to the ionized α,β-unsaturated oxime and the EI-induced cycloreversion yielding ionized β-methylstyrene, or the ionized form of a zwitterionic intermediate, which had been proposed previously for the addition/cycloaddition mechanism(s) in the solution phase, currently under study.     

-Cyclisation of tertiary amines. Part 4. Cyano-imidoyl substituted furans from captodative enamines and dibenzoylacetylene

-Cyano-enamines and dibenzoylacetylene lead to dienes (via [2+2] cycloaddition followed by ringopening). Their -Cyclisation to oxygen produces the title compounds.     

Flash vacuum thermolysis of 1,5-Bis-(1-chloroethenyl)anthracene. The thermal conversion of cyclopent[hi]aceanthrylene into cyclopent[hi]acephenanthrylene

Flash Vacuum Thermolysis of 1,5-bis-(1-chloroethenyl)anthracene (6) gives cyclopent[hi]-aceanthrylene (2) which at T≥9000 °C rearranges to cyclopent[hi]acephenanthrylene (1). This conversion occurs more readily than that of the monocyclopenta-fused aceanthrylene to acephenanthrylene.     

Photoageing of rigid PVC—I. Films containing Ca/Zn thermal stabiliser

The photo-oxidation (λ > 300 nm, T = 40, 55 and 70 °C) of ˜80μm films of PVC stabilised by Ca and Zn stearates was studied using gravimetry, IR and UV-visible spectrophotometry. The stabilisers disappear in the early days of exposure according to a pseudo first-order process, presumably by HC1 scavenging, which gives an idea of the rate of HC1 release during this period. The concentration of polyenes absorbing at λ = 500 nm begins to increase rapidly when the stabiliser is totally consumed. At the same time, weight loss takes place, showing that there are more HC1 elimination events than oxidation events. These results are consistent with the following hypotheses: (a) oxidation is diffusion controlled; (b) long polyene formation is HC1 catalyzed; (c) conjugated sequences—(CH₂ = CH₂)_n—with n = 10–12 result essentially from a thermal process; (d) the rate of carbonyl and hydroxyl build-up is nearly not influenced by the increase in polyene concentration or rate of HCl evolution which can also be explained, at least partially, in terms of O₂ diffusion control of oxidation kinetics.     

Freezing of water bound in lichen thallus as observed by H NMR. II. Freezing protection mechanisms in a cosmopolitan lichen Cladonia mitis and in Antarctic lichen species at different hydration levels

Proton NMR spectra at 300 MHz for dehydrated and hydrated thallus of Cladonia mitis Sandst. [=C. arbuscula (Wallr.) Flot ssp. Mitis (Sandst.) Ruoss], Himantormia lugubris (Hue) Lamb and Usnea aurantiaco-atra (Jacq.) Bory were recorded. The temperature was decreased from room temperature down to −45 °C. Pulse length was set to π/2=8.3 μs, which allowed the observation of tightly bound and loosely bound/or free water fraction, whereas the signal from solid matrix of thallus was reduced. In hydrated thallus a narrow Lorentzian line coming from loosely bound/free water fraction was recorded. For the temperature range between −5 and −20 °C a discontinuous increase in line halfwidths, accompanied by a decrease in area under the peak, was observed. This was attributed to the cooperative freezing of bulk water present in lichen thallus. In dehydrated thallus the NMR line consists of two components: a narrow, Lorentzian one (coming from loosely bound/free water fraction) and a broad line (from water tightly bound in lichen thallus). The overall area under peak remains unchanged down to −5 °C, and then between −5 and −20 °C it continuously decreases due to non-cooperative water immobilisation. As the temperature is decreased, for temperatures above −5 °C, the contribution made by the broad line component increases at the expense of the narrow line component. The mechanism of loosely-to-tightly bound water transfer is, at least partially, responsible for the freeze-protection of thallus in the lichen species investigated. No significant differences between the freeze protecting loosely-to-tightly bound water transfer mechanism of Antarctic lichens and that of cosmopolitan lichens was noticed.     

- and β-cyclodextrin complexes with n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates. A molecular mechanics study of 1:1 and 1:2 associations

Molecular mechanics (MM) methods were employed to evaluate stabilization upon formation of inclusion compounds between two different guest molecules and - and β-cyclodextrins (CDs) for two different stoichiometries 1:1 and 1:2. The two guest molecules studied were n-alkyl carboxylic acids and n-alkyl p-hydroxy benzoates with variety of chain lengths. The computed stability for the inclusion compounds between -CDs and n-alkyl carboxylic acids reproduced experimental data reported in the literature. The transition between 1:1/1:2 complexes occurred at an alkyl chain length of n_C=9. It was previously demonstrated by diffusion coefficients measures that a stable 1:2 stoichiometry inclusion compound could be formed between n-alkyl p-hydroxy benzoates and -CD for the chain length n_C>4. The computed results reproduced the experimental ones. The combination between OPLS and GB/SA resulted in better agreements with experiments than those obtained with MM2 and MM3.     

Reaction of N-vinylindazolium and N-vinylbenzotriazolium salts with nucleophiles

Reaction of N-vinylindazolium tetrafluoroborates with aqueous potassium carbonate or sodium borohydride affords 2,3-dihydroquinazolines which evolve to 1,2,3,4-tetrahydroquinazolines by intra or intermolecular nucleophilic attack. The X-ray structure of one tetrahydroquinazoline, the tricyclic compound 17a, was determined (C₁₄H₁₆N₂O₅, P2₁/n, a=6.001(4)Å, b=13.601(8)Å, c=17.452(6)Å, β=94.93(3)°, V=1419(1)ų, Z=4, R=0.078 for 1541 observed reflexions). Only open-chain compounds are obtained when these salts react with methanol. 2-Vinylindazolium and 3-vinylbenzotriazolium tetrafluoroborates react with aqueous potassium carbonate and with sodium borohydride yielding the corresponding neutral benzazoles by cleavage of the azole-vinyl bond. They add methanol to the exocyclic double bond and, in the case of indazole derivative, an expansion to a 1,2-dihydroquinazoline is observed in basic medium.A general mechanism is proposed for the reaction of vinylpyrazolium and indazolium salts with nucleophiles.     

Thermal solid–solid interactions and physicochemical properties of NiO/Fe2O3 system doped with K2O

The effects of calcination temperature and doping with K₂O on solid–solid interactions and physicochemical properties of NiO/Fe₂O₃ system were investigated using TG, DTA and XRD techniques. The amounts of potassium, expressed as mol% K₂O were 0.62, 1.23, 2.44 and 4.26. The pure and variously doped mixed solids were thermally treated at 300, 500, 750, 900 and 1000 °C. The catalytic activity was determined for each solid in H₂O₂ decomposition reaction at 30–50 °C. The results obtained showed that the doping process much affected the degree of crystallinity of both NiO and Fe₂O₃ phases detected for all solids calcined at 300 and 500 °C. Fe₂O₃ interacted readily with NiO at temperature starting from 700 °C producing crystalline NiFe₂O₄ phase. The degree of reaction propagation increased with increasing calcination temperature. The completion of this reaction required a prolonged heating at temperature >900 °C. K₂O-doping stimulates the ferrite formation to an extent proportional to its amount added. The stimulation effect of potassium was evidenced by following up the change in the peak height of certain diffraction lines characteristic NiO, Fe₂O₃, NiFe₂O₄ phases located at “d” spacing 2.08, 2.69 and 2.95 Å, respectively. The change of peak height of the diffraction lines at 2.95 Å as a function of firing temperature of pure and doped mixed solids enabled the calculation of the activation energy (ΔE) of the ferrite formation. The computed ΔE values were 120, 80, 49, 36 and 25 kJ mol⁻¹ for pure and variously doped solids, respectively. The decrease in ΔE value of NiFe₂O₄ formation as a function of dopant added was not only attributed to an effective increase in the mobility of reacting cations but also to the formation of potassium ferrite. The calcination temperature and doping with K₂O much affected the catalytic activity of the system under investigation.     

Oxygen abstraction from tetrahydrofuran by molybdenum-iodide complexes. X-ray molecular structure of [Mo2(μ-O)(μ-I)(μ-O2CCH3)I2(THF)4][MoOI4(THF)] (THF = tetrahydrofuran)

The interaction between Mo₂(O₂CCH₃)₄, Me₃SiI and I₂ in THF resulted in oxygen abstraction from the solvent and formation of [Mo₂(μ-O)(μ-I)(μ-O₂CCH₃) I₂(THF)₄]⁺[MoOI₄(THF)]⁻ and I---(CH₂)₄---I. The molybdenum complex has been characterized by X-ray diffractometry. Crystal data: triclinic, space group P , a = 13.827(3) Å; b = 15.803(7) Å; c = 9.950(3) Å; = 93.34(4)°; β = 102.40(2)°; γ = 90.09(2)°; V = 2120(2) Å₃; Z = 2; d_calc = 2.559 g cm⁻³; R = 0.0476 (R_w = 0.0613) for 370 parameters and 3938 data with F₀²> 3σ(F₀²). The metal-metal distance in the cation is 2.527(2) Å and indicates a strong interaction. The magnetic behavior is consistent with the assignment of one unpaired electron to the Mo₂⁷⁺ core of the cation and one to the d¹ Mo(V) center of the anion. The interaction between Mo(CO)₆ and I₂ in THF also results in the formation of 1,4-diiodobutane.     

Chemie der schweren carben-analogen R2M, M = Si, Ge, Sn : XVIII. Eine unerwartete Ge---C-Spaltung des als Dimethylgermylen-Speicher dienenden 7,7-Dimethyl-7-germanorbornadiens

During thermolysis of the 7-germanorbornadiene 1 in chlorobenzene at 70°C in the presence of concentrated hydrochloric acid, besides the well-known formation of free germylene Me₂Ge and its consecutive product dimethylchlorogermane 2, the polar splitting of only one Ge---C bond in 1 has been observed for the first time. It does not yield Me₂Ge, but instead it rapidly forms the 1-germyl-1,4-dihydronaphthalene 3. The kinetics of this reaction at 53°C are of 2nd order, t_1/2 = 20 min, k = 0.22 l mol⁻¹ min⁻¹. At room temperature 3 is formed quantitatively. Also, at 70°C the slower formation of the germylene Me₂Ge from 1 can be suppressed completely if HCl gas is bubbled through the reaction mixture, thus favouring the rapid formation of 3. As a by-product the 1,2-dihydronaphthalene 5 is generated.     

Solid products from thermal decomposition of polyethylene terephthalate: Investigation by CP/MAS 13C-NMR and fourier transform-IR spectroscopy

The solid reaction products from pyrolysis of polyethylene terephthalate in the presence and absence of red phosphorus were characterized by CP/MAS ¹³C-NMR, FR-IR, and MAS ³¹P-NMR spectroscopy. Over the temperature range of 300–400°C, polyethylene terephthalate was converted in a sealed vial to a highly crosslinked polymer of terephthalic acid. Pyrolysis in the presence of red phosphorus, which functions as a flame retardant by increasing the amount of char, yielded an intractible polyaromatic phosphate ester. After thermal cleavage of polyethylene terephthalate with formation of free carboxyl and vinyl ester groups, there are two competing reaction pathways. The smaller molecular weight fragments may enter the vapor phase where they undergo further degradation primarily to CO₂, CO, and acetaldehyde, as described by others. However, if volatilization of the oligomeric fragments is inhibited, an alternate reaction pathway gives rise to the formation of highly crosslinked char. Red phosphorus decreases the volatility of the oligomeric fragments by converting them to phosphates and thereby enhances char formation.     

Cyclization by the intermediates of phenylthio- and phenoxy carbamoyl. Formation of azasuccinic anhydrides and their polycondensation products. Intervention of the carbamoyl pyridinium cation

The N-(p-nitrophenoxy-carbonyl) derivatives of glycine, DL -alanine and DL -leucine are transformed by the action of pyridine into azasuccinic, 3-methyl-2-azasuccinic and 3-isobutyl-2-azasuccinic anhydride, respectively. These cyclisations occur probably via the intermediate N-carbamoyl-pyridinium cation , the rate of cyclisation seems to depend on the concentration of the intermediate in the form of the dipolar ion , i.e. the ionised carboxyl is necessary for the reaction. In γ-collidine the cyclisation occurs very slowly; this is attributed to the slowness due to steric hindrance of the production of N-carbamoyl-γ-collidinium cation and its instability. The azasuccinic anhydrides mentioned polycondense, yielding the corresponding polyglycine, poly-DL -alanine and poly-DL -leucine. This reaction too is catalysed by pyridine; it can also be effected by γ-collidine, but the efficacity of the latter in comparison with pyridine is even less than in the catalysis of the cyclisation described above. N-(p-nitrophenoxy-carbonyl)-glycine reacts with lysozyme in the presence of pyridine; several glycine residues are introduced into the enzyme molecule, the product being insoluble and poorly active.     

Reactions of N- and C-alkenylanilines: VI. Synthesis of 6-methyl-2-[(E or Z)-1-propenyl]anilines and the corresponding anilides and their reaction with bromine

Isomerization of 2-allyl-6-methylaniline by the action of potassium hydroxide at 300°C afforded cis and trans isomers of 2-methyl-6-(1-propenyl)aniline which were converted into the corresponding carbamates by treatment with ethyl chloroformate. Ethyl 2-methyl-6-(1-propenyl)phenylcarbamates reacted with bromine to give mixtures of 4-(1-bromoethyl)-8-methyl-1,4-dihydro-2H-3,1-benzoxazin-2-one and ethyl 2- methyl-6-(1,2-dibromopropyl)phenylcarbamates. Treatment of the same compounds with N-bromosuccinimide resulted in formation of 2-ethoxy-4H-3,1-benzoxazine derivatives. The reaction of N-{6-methyl-2-[(Z)- 1-propenyl]-phenyl}methanesulfonamide gave a mixture of stereoisomeric N-[6-methyl-2- (1,2-dibromopropyl)-phenyl]-methanesulfonamides.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 40, No. 12, 2004, pp. 1815–1818.Original Russian Text Copyright © 2004 by Afonkin, Sotnikov, Gataullin, Spirikhin, Abdrakhmanov.For communication V, see [1].