ISSN:0021-8383    

DOI:10.1002/prac.19853270102

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

4′‐tert‐Alkylbenzo[15]Crown‐5‐Ether. Syntheses and Complexes with Potassium ThiocyanateThe title compounds4are synthesized either by alkylation of pyrocatechole1in 4‐position and followed by ring closure with 1,11‐dichloro‐3,6,9‐trioxaundecane or by alkylation of benzo[15]‐crown‐53. In most cases the way first mentioned gives better results. Analytical samples of the alkylated benzo[15]crown‐5 ethers4are obtained through complexing with KSCN.Physical data and1H‐n.m.r.‐spectra of 5 new pyrocatecholes2and 6 new benzo[

ISSN:0021-8383    

DOI:10.1002/prac.19853270103

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

On the Pyrolysis of Unsubstituted Cyclanes – Selectivity of the Formation of Reaction Products, Kinetic Parameters, Mechanistic InterpretationsThe thermal decompostion of cyclopentane (1), cyclohexane (2), cycloheptane (3), cyclooctane (4), cyclodecane (5), and cyclododecane (6) was studied in a laboratoryscale metallic tubular reactor at 650 to 850°C in the presence of steam. The kinetic parameters for the overall reactions were determined and the gaseous as well as the liquid reaction products were analyzed and identified by gas chromatography or by the coupling of gas chromatography and mass spectrometry, respectively. It could be shown that from all cyclanes the isomeric α‐olefines are formed, if the conversion of the starting cyclanes is small. This supports the view that the cyclane → α‐olefin isomerization is an important initial reaction in pyrolysis of1up to6. The results also demonstrate that the main pathway of degradation is a radical chain mechanism via cyclanyl radicals with β(CC) bond scission and 1.4 or 1.5‐H‐isomerization of alkenyl radicals as the most importa

ISSN:0021-8383    

DOI:10.1002/prac.19853270104

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractPhotoexcited zink tetraphenylporphyrin (ZnTPP) reacts with arene diazonium salts via electron transfer according to the oxidation mechanism. This is proved by ESR spectroscopy of ZnTPP+formed and the fact that N2and ZnTPP+are formed in a molar ratio.Due to very different life‐times of1(ZnTPP)* and3(ZnTPP)*it is possible to differentiate between singlet and triplet electron transfer reactions using different diazonium salt concentrations. In this way, the respective quenching constants are determined by means of flash spectroscopy.Due to electron back transfer the singlet reaction at high concentrations of diazonium salts (0.1M) is inefficient (quantum yield 0.1), whereas back electron transfer is symmetry‐forbidden in the triplet reaction which, therefore, proceeds with high quantum yields, mearly reaching the ISC quantum yield.From differences between the triplet quenching constants determined by flash spectroscopy and from product quantum yields, respectively, and from corresponding kinetic models it is concluded that the triplet reaction proceeds via a reversibly formed triplet exciplex.Complexes of meso tetraphenyl porphyrin containing Pb(II), Sn(IV), Mn(II), Ni(II), Cu(II) and Fe(III), respectively, have lower sensitization activities decreasing in the order, given in the t

ISSN:0021-8383    

DOI:10.1002/prac.19853270105

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

A New Synthesis of 4,5‐Dihydroxy‐pyrazoles1‐Aryl‐pyrazolin‐5‐ones1are converted by Knoevenagel condensation with acetone or by reaction with 2,2‐dimethyl‐1,3‐dioxolane6to 1‐aryl‐4‐isopropyliden‐pyrazolin‐5‐ones2. The compounds2are epoxidized by hydrogen peroxide forming the spiro‐epoxides3, which can be cleaved to 4,5‐dihydroxy‐pyrazoles4under acidic conditions. 4‐Acetoxy‐5‐hydroxy‐pyrazoles13are formed directly, when3are cleaved in presence of acetic anhydride. The 3,3′,3′‐trimethyl‐1‐(4‐nitro‐phenyl)‐pyrazolin‐4‐spiro‐2′‐oxir

ISSN:0021-8383    

DOI:10.1002/prac.19853270106

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Electrochemical Carboxylation of Cinnamoyl‐1,1‐bis(alkylthio)ethylenesCinnamoyl‐1,1‐bis(alkylthio)ethylenes (1a–1h) are reduced electrochemically in the presence of carbondioxide in aprotic media. The attack of CO2takes place either in 1‐ or 5‐position of cinnamoyl‐1, 1‐bis(alkylthio)ethylenes (1a–1h) depending on the nature of the aryl substituents. If CO2reacts in position 1 carbonic acids3are obtained, reaction of carbondioxide in 5‐ position leads to the acids2. The effects of different aryl substituents on the halfwave potentials and the preparative electrolyses h

ISSN:0021-8383    

DOI:10.1002/prac.19853270107

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Photochemistry of Aminoketones. VIII. Diastereoselective Synthesis of 3‐Hydroxy‐prolinesGlycine esters react in two steps (aminoalkylation and N‐acylation) to N‐acyl‐N‐(β‐benzoylethyl)‐glycine ester3. In less polar solvents these ketonic compounds are n,π*‐excited by 300 nm irradiation. In ether3*yield mixtures of aminocyclopropanoles4, hydroxyprolines5and products of additions and cleavages. In benzene and cyclohexane/benzene, respectively, the regioselective photocyclization to5is favoured. Furthermore this hydroxyproline synthesis has the advantages of high diastereoselectivity yielding the (2,3) E–5and of high overall‐yields in connection with the one pot method. The influence of solvents and substituents on the regio‐ and diastereoselectivity are explained using a model with stabilization of special conformations of intermediates by

ISSN:0021-8383    

DOI:10.1002/prac.19853270108

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Nitrogen‐15 and Carbon‐13 Chemical Shifts and13C‐1H,13C‐15N and15N‐15N Coupling Constants of Parasubstituted Arene Diazonium SaltsNitrogen‐15 and carbon‐13 chemical shifts and13C‐1H,13C‐15N and15N‐15N coupling constants of15N‐enriched p‐substituted arene diazonium salts are reported and within the ΔE‐approximation investigated. It is shown that changes of ΔE should be taken into account when considering variation of the nitrogen‐15 chemical shifts. The influence of substituent effects was discussed within the DSP (dual su

ISSN:0021-8383    

DOI:10.1002/prac.19853270109

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Electrochemical Reduction and Azo‐coupling of Ring Chlorinated p‐Dimethylaminobenzenediazonium Salts. Hammett‐CorrelationsThe polarographic half‐wave potentials of ring halogenated 4‐dimethylaminobenzenediazonium salts (6a–6j) can be linearly correlated with the total σ‐constants Σσkorr(E1/2= (0.25 Σσkorr+ 0.33) V; r = 0.995), if for the dimethylamino group of the 3‐ or 3,5‐halogenated derivatives corrected σ′p‐constants are used. The Σσkorr‐values determined can be used to correlate the influence of substituents on the azo‐coupling kinetic

ISSN:0021-8383    

DOI:10.1002/prac.19853270110

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractAttempts to rearrange a β‐hydroxy‐alkyne with a secondary hydroxy group into an α,β‐unsaturated ketone failed in the case of a potential prostaglandin intermediate. However, it was possible to convert this intermediate into 13‐hydroxy‐5(Z)‐prosten‐15‐ynoic acids, which are interesting prostaglandin analogues with a modifie

ISSN:0021-8383    

DOI:10.1002/prac.19853270111

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY