Photochemically generated silicon—carbon double-bonded intermediates : XII. Some properties of silacyclopropenes and silapropadienes produced by photolysis of ethynylpolysilanes

The photolysis of six ethynyl-substituted polysilanes has been investigated in the presence or absence of methanol. Irradiation of 1-ethynyl-2-phenyl- and 1-ethynyl-1-phenyltetramethyldisilane (I and II), 1-ethynyl-1,1-diphenyltrimethyldisilane (III) and 2-ethynylheptamethyltrisilane (V) in the presence of methanol produced methoxysilanes arising from the corresponding reactive silacyclopropene and silapropadiene intermediates. Irradiation of 1-enthynylheptamethyltrisilane (IV) led to the formation of dimethylsilylene, ethynylpentamethyldisilane and 1,1-dimethyl-2-pentamethyldisilanyl-1-silacyclopropene intermediate. The photolysis of tris(trimethylsilyl)ethynylsilane (VI) in the presence of methanol produced 1-trimethylsilyl-1-bis(trimethylsilyl)methoxysilylethene and hexamethyldisilane. Photolysis of II and III in the absence of a trapping agent gave the respective bis(silyl)acetylenes, via a 1,2-hydrogen shift, from the transient silacyclopropenes, in moderate yields, whereas the yields of the rearranged acetylenes from IV and V were low.     

Photochemistry of cyclic vicinal tricarbonyl compounds Photolysis of alloxan in the presence of olefins containing allylic hydrogen

UV irradiation of an acetone solution of alloxan (1) in the presence of olefins containing allylic hydrogen leads to the formation of 5-hydroxy-5-alkenyl barbituric acids (2) resulting from an initial hydrogen abstraction process. On the other hand, photolysis of 1 with ethyl-1-propenyl ether yields [2+2] (oxetanes) and [4+2] (dioxenes) photocycloaddition products, beside the corresponding hydrogen abstraction products. When the irradiation was performed with olefins containing electron-acceptor substituents, product formation could not be observed.     

1,2-dioxetanes as chemiluminescent intermediates in the triplet oxygen oxygenation of olefins.

Several enol ethers react in the dark at elevated temperatures with triplet oxygen, producing ketones and chemiluminescene. Other electron-rich olefins were investigated.     

Studies on the syntheses of azole derivatives. Part VIII. Photolysis of N-aryl-N-benzylearbamoyl azides [studies on the syntheses of heterocyclic compounds. Part CDXV

Photolysis of N-benzyl-N-phenylearbamoylazide (IVc) afforded 1-benzy 1-2-benzimidazolinone (Ic), 2-benzimidazolinone (IIe), 4-benzy 1-2-benzimidazolinone (IIe), and 5-benzy1-2-benzimidazo-linone (IIf)- The same reaction of N-benzyl-N-(4-chlorophenyl) carbamoyl azide (IVd) gave 3-benzyl-1-(phenylhydrazocarbonyl)-2-benzimidazolinone (VIb) besides the above four products. In the case of N-benzyl-4-(4-butoxyphenyl)carbamoyl azide (IVe), 1-benzy1-5-butoxy-2-benz-imidazolinone (1e), 5-butoxy-2-benzimidazolinone (IId), 5-benzy1-2-benzimidazolinone (IIf), and 4-benzy1-6-butoxy-2-benzimidazolinone (IIg).     

Photolysis of carbon tetrachloride in the presence of alkanes

The photolysis of carbon tetrachloride in the presence of a number of alkanes has been investigated in the gas phase. The products obtained from the photolysis experiments were those expected from a chain reaction in which trichloromethyl radicals abstract hydrogen atoms from the alkane. The data have been used to determine Arrhenius parameters for hydrogen abstraction from the series of alkanes CH₄, C₂H₆, C₃H₈, and i-C₄H₁₀ by trichloromethyl radicals, The rate data obtained are used to explain why termination reactions involving alkyl radicals become less significant as the alkane becomes more complex.     

Photolysis of 2-mercaptobenzothiazole in the presence of surfactants

The quantum yield of the photolysis of 2-mercaptobenzothiazole (MBT) in the molecular form increases by a factor of 20 in the presence of the surfactants cetyltrimethylammonium bromide (CTAB) and cetylpyridinium chloride (CPCl) in comparison with aqueous solution. In the photolysis of the MBT ionic form, the quantum yield does not change in the presence of CTAB and decreases in the presence of CPCl. The maximums of the MBT absorption spectra shift with an increase in the surfactant concentration for both the molecular and ionic forms. Simultaneously, the MBT photolysis quantum yield increases. It has been shown that the quantum yield of MBT photolysis in water increases in the presence of compounds containing heavy atoms.     

Photolysis of 3-nitrophenyl azide: Trapping the reactive intermediates

Irradiation of 3-nitrophenyl azide gives four trappable intermediates; the singlet nitrene, two isomeric dehydroazepines, and the triplet nitrene.     

Photolysis of sulfur dioxide in the presence of foreign gases: VII. Acetylene

SO₂ was photolyzed at 25°C and 3130 Å in the presence of acetylene. The quantum yield of the sole gas-phase product, CO, was determined for a wide range of SO₂ and C₂H₂ pressures, and in the presence of CO₂, NO and H₂O. The quantum yield, Φ{CO}, increases with the ratio [C₂H₂] [SO₂] to an upper limiting value of 0.052. In the presence of excess CO₂ or H₂O vapor, Φ{CO}becomes independent of [SO₂] and is reduced at low values of [C₂H₂] but remains unchanged or increases slightly at high values of [C₂H₂]. As NO is added at the higher C₂H₂ pressures it first increases Φ{CO} but then reduces it to zero. None of the CO comes from singlet states as shown by the strong quenching of CO production by NO. Both of the two non-emitting triplet states previously proposed to be important in the photochemistry of SO₂, as well as the emitting triplet, are necessary to interpret the results of this study. A relatively complete mechanism is presented, all the pertinent rate coefficient ratios are obtained, and from these, values of Φ{CO} are computed. They agree well with the observed values.     

Ozonolysis of olefins VIII. Synthesis of phenoxyacetaldehydes by ozonolysis of allylphenylethers

Summary A new route for the preparation of a series of phenoxyacetaldehydes (2a–j) which are useful intermediates or products, is described. It starts from the easily available allylphenylethers1a–j which are ozonized at –40 °C and further treated with dimethylsulfide to give solutions of the corresponding phenoxyacetaldehydes2a–j; these are purified by column chromatography. Reaction of2a–j with 1-methyl-1-phenylhydrazine leads to the corresponding hydrazones3a–c,3e–g,3i, and3j. The aldehydes can also be transformed into the stable dimethylcetals4a,4e,4h, and4i by reaction with trimethyl orthoformate.

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Ozonolyse von Olefinen, 8. Mitt. Synthese von Phenoxyacetaldehyden durch Ozonolyse von Allylphenylethern

Zusammenfassung Ein neuer Weg, die als Synthone nützlichen Phenoxyacetaldehyde2a–j darzustellen, wird beschrieben. Dazu werden die leicht zugänglichen Allylphenylether1a–j bei –40 °C ozonisiert und anschließend mit Dimethylsulfid reduziert, um Lösungen von2a–j zu erhalten. Reaktion von2a–j mit 1-Methyl-1-phenylhydrazin führt zu den entsprechenden N-Methyl-N-phenylhydrazonen3a–c,3e–g,ei und3j. Die Aldehyde können auch durch Reaktion mit Trimethylorthoformiat in die stabileren Dimethylacetale4a,4e,4h und4i übergeführt werden.

     

Carbonylation of olefins in the presence of palladium catalysts

Conclusions Palladium complexes of the general formula PdCl₂L₂ (L=tri(thienyl)phosphine) are active and selectively reacting catalysts in the carbonylation of C₂-C₁₈ -olefins.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2245–2248, October, 1987.     

Active intermediates in the oxidative bromochlorination of olefins in concentrated hydrochloric acid

A study was carried out on the oxidative bromochlorination of olefins in the presence of KBr using hydrogen peroxide and an electrochemical technique. Asymmetric trihalide anions, Br₂Cl⁻ and BrCl₂ ⁻, were found to be the active bromochlorination reagents. The reaction mechanism was discussed. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya St., 253660 Kiev-94. Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 33, No. 4, pp. 248–251, July–August, 1997.     

Copper-catalyzed allylations of zirconocene intermediates generated from o-alkenyl or o-alkynylbenzyl ether derivatives and zirconocene-butene complex

o-Alkenyl or alkynyl benzylzirconocene intermediate, which was readily generated by the reaction of 2-alkoxymethylstyrene or 2-alkoxymethyl-1-(trimethylsilylethynyl)-benzene derivative with zirconocene-butene complex (Negishi reagent, "Cp2Zr"), reacted with allyl or propargyl halides in the presence of a catalytic amount of CuCl to give allylation or allenylation products. Conversion to Dane's diene, which is a key intermediate for estrone synthesis, was efficiently carried out by enyne olefin metathesis of the allylation products.     

Photolysis of organopolysilanes. The reaction of photochemically generated trimethylsilyphenylsilylene with alkyl chlorides

Photochemically generated trimethylsilylphenylsilylene reacted with octyl chloride and cyclopropylcarbinyl chloride to give the respective formal carbon-chlorine insertion products. With sec-butyl chloride, trimethylsilylphenylsilylene afforded both the carbon-chlorine insertion product and 1-chloro-1phenyl-2,2,2-trimethyldisilane (IV), while with tert-butyl chloride, IV was obtained as the sole volatile product.     

Photolysis of organopolysilanes. The reaction of photochemically generated methylphenylsilylene with conjugated dienes

Photolysis of 2-phenylheptamethyltrisilane (I) in the presence of acyclic and cyclic conjugated dienes has been investigated using both a high-pressure mercury lamp with a quartz filter and a low-pressure mercury lamp with a Vycor filter. Irradiation of I in the presence of 1,3-butadiene, isoprene or 2,3-dimethylbutadiene with a high-pressure mercury lamp gave a product arising from photochemical isomerization of a silacyclopropane derivative and a compound apparently formed by 1,4-silylene addition, along with a 1/1 “ene” adduct of the diene to a photo-rearranged intermediate containing the silicon—carbon double bond. Irradiation of I in the presence of the conjugated diene with a low-pressure mercury lamp, followed by treatment of the product with methanol, afforded a methoxysilane arising from methanolysis of the corresponding silacyclopropane, together with the isomerization product, silacyclopentene and rearranged addition product. Irradiation of I in the presence of cyclopentadiene with a high-pressure mercury lamp produced methylphenylsilylcyclopentadiene, while irradiation of a similar mixture with a low-pressure mercury lamp followed by treatment with methanol gave 4-(methoxymethylphenylsilyl)-1-cyclopentene. With 1,3-cyclooctadiene, the photochemically generated methylphenylsilylene afforded many types of addition product. Photolysis of I in the presence of 1,3-cyclohexadiene, however, afforded none of the silylene addition products.     

Photochemically generated stable cation radical of phenothiazine aggregates in mildly acid buffered solutions

This work characterizes, for the first time, the photochemical behavior of the antipsychotic drugs thioridazine (TR), trifluoperazine (TFP), and fluphenazine (FP) influenced by the aggregation state of the molecules. Samples of monomeric and aggregated forms of phenothiazines were submitted to 20 min of irradiation at 254 nm for intervals of 1, 5, 10, 15, 20, or 25 days. In high phenothiazine concentrations, the irradiation led to the appearance of absorbance bands in the visible region peaking at 633 nm for TR and 509 nm for FP and TFP. In the dark, at room temperature and at 4 degrees C, these bands disappeared, after approximately 15 and approximately 60 min, respectively, but reappeared after a new irradiation session. These visible bands were assigned to stable cation radicals that were characterized by direct EPR measurements and by flash photolysis. Photogenerated stable cation radicals in the phenothiazine aggregates at room temperature are formed probably due to the stacking of the thiazine phenyl moieties. For the monomeric forms of phenothiazines, the spectral changes observed during the irradiation suggested the formation of sulfoxide and hydroxylated derivates. Oxidized derivates were detected by mass spectrometry of the aggregated forms of phenothiazines (>100 microM) only in the samples irradiated for more than 20 days. In contrast, monomeric phenothiazines were totally converted to the oxidized forms after 20 min of irradiation. Surface tension measurements of phenothiazines revealed that, in concentrations above 100 microM, the drugs formed aggregates. In the case of TR, small-angle X-ray scattering measurements indicated that this compound forms large lamellar-like aggregates in aqueous solutions.     

Photolysis of α-diazo carbonyl compounds in the presence of imidazole. A new method for the preparation of nor olefins and its application to bile acid side chain degradation

α-Diazomethyl ketones derived from carboxylic acids are photolyzed in the presence of imidazole to give the corresponding nor olefins or, in the case of aryl diazo ketones, the corresponding, stable imidazolides. The application of the method to a novel degradation of bile acid side chain is reported.     

Mild alkoxycarbonylation of olefins in the presence of palladium complexes

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, p. 743, March, 1989.     

Ozonolysis of 1,4-cyclohexadienes in the presence of methanol and acid. Mechanism and intermediates in the conversion of 1,4-cyclohexadiene derivatives to beta-keto esters

Conditions for the preparation of beta-keto esters directly from 1,4-cyclohexadiene derivatives are described. This procedure is a further step in the application of the synthetic methodology, which consists of the combination of Birch reduction of available benzene derivatives followed by ozonolysis. In this work, the syntheses of derivatives of dimethyl gamma-keto-alpha-aminoadipate and dimethyl beta-keto glutamate from the corresponding 1,4-cyclohexadiene derivatives are described. The latter compounds are prepared from phenylalanine and phenylglycine, respectively. The study of the ozonolysis of simple alkyl derivatives of 1,4-cyclohexadiene in the presence of methanol, both in the presence and absence of acid, helped to establish the mechanism of this reaction. The proximity of the two double bonds, which are cleaved, leads to the intermediate formation of 1,2-dioxolane derivatives that could be identified by NMR spectroscopy. It is shown that regardless of the regioselectivity of the cleavage of the primary ozonide, which is formed, all 1,2-dioxolane derivatives can lead to beta-keto esters. This is due to the equilibrium between these dioxolanes in the presence of methanol and acid.