bluuebunny/crossref_metadata_2025_split huggingface dataset:
Zur Ring‐Ketten‐Tautomerie und Reaktionen eines bicyclischen 1‐Hydroxy‐3‐imidazolin‐3‐oxids
Authors: Schulz Manfred , Mögel Liena , Römbach Joachim 
Published: December 2004

Ring‐Chain Tautomerism and Reactions of a Bicyclic 1‐Hydroxy‐3‐imidazoline‐3‐oxideThe reaction of 8‐hydroxy‐1, 4, 5, 7‐tetramethyl‐6,8‐diaza‐bicyclo[3.2.1]‐oct‐6‐en‐6‐oxide (1), a 2,5‐bridged bicyclic 1‐hydroxy‐3‐imidazoline‐3‐oxide, with NaBH4, dimethyl acetylene dicarboxylate and methylmagnesiumiodide, respectively, yields derivatives of the ring opened isomer 2. Whilst on reaction with phenylisocyanate the bicyclic structure 1 is preserved and the urethane 3 is formed. The ring‐chain tautomerism of 1 is important for the application of 1 as a spin trap or radical scavenger.
Radikalabfang. III [1] ESR‐spektroskopische Untersuchung von Radikalreaktionen eines bicyclischen 1‐Hydroxy‐3‐imidazolin‐3‐oxids [2]
Authors: Reinhardt Michael , Schulz Manfred , Römbach Joachim 
Published: December 2004

Spin Trapping. III. Studies of Radical Reactions of a Bicyclic 1‐Hydroxy‐3‐imidazoline‐3‐oxideRadical addition reactions to the nitrono group and the oxidation of the 8‐hydroxy‐1,4,5,7‐tetramethyl‐6,8‐diazabicyclo[3.2.1]oct‐6‐en‐6‐oxide 2b were investigated by e.s.r.‐spectroscopy. Oxidation of 2b by Ag2O, PbO2, hydrogenperoxide, tert.‐butoxy and benzoyloxy radicals, respectively, yields a bicyclic nitroxide with typical a(N)‐value (1,9 mT). Testing a wide range of carbon‐centered radicals we did not find, however, any spin adducts in contrast to the literature. Only H‐atoms are found to add to the nitrone function of 2b giving a bicyclic nitroxide 4b (R′ = H) with a(N)‐value of 1,4 mT, a(Hax) = 2,4 mT. The relationship between a ring‐chain tautomerism of 2 as previously described and the formation of radicals has been demonstrated by radical reactions of derivatives of ring opened isomers 5b.
Synthese von 5‐Nitro‐2,3‐dihydrobenzo(b)furanen aus 2‐Methylen‐triethyl‐ammonio‐4‐nitrophenolat und 2‐Chlor‐1,3‐dicarbonylverbindungen
Authors: Fanghänel E. , Böckelmann J. , Grossmann N. , Pfeifer D. 
Published: December 2004

Synthesis of 5‐Nitro‐2,3‐dihydrobenzo(b)furanes from 2‐Methylenetriethyl‐ammonio‐4‐nitrophenolat and 2‐Chloro‐1,3‐dicarbonyl Compounds2,2‐Disubstituted 5‐nitro‐2,3‐dihydrobenzo[b]furanes 6a–c were synthezised in a one step procedure starting from 2‐methylene‐triethyl‐ammonio‐4‐nitrophenolat 2 and 2‐chloro‐1,3‐dicarbonyl compounds 4a–c. The structure of 6a–c was determined chemically and by 13C‐n.m.r.‐spectroscopy.
Inkrementsystem zur Beschreibung der Lage von Ionenpaar‐Charge‐Transfer‐Banden in Wasser und nichtwäßrigen Lösungsmitteln
Authors: Hennig Horst , Benedix Roland , Billing Roland 
Published: December 2004

Increment System for Predicting of the Position of Ion Pair Charge‐Transfer Bands in Water and Non‐aqueous SolventsThe energy of the absorption maximum of ion‐pair charge‐transfer bands, ΔGCT, occuring in addition to the absorptions of the single ions, is approximately the sum of contributions (increments) of the ions concerned. On the basis of spectroscopic data, an increment system for predicting of ΔGCT in aqueous solution has been proposed. A linear relationship between the increments and the standard electrode potentials of ions has been found, permitting the expansion of the increment system. The difference between calculated and experimental values does not exceed 2500 cm−1. The applicability of the increment system to non‐aqueous solvents has been proved in several cases.
Push‐pull‐Butadiene. VI. Darstellung von substituierten Nicotinonitrilen
Authors: Peseke K. , Michalik M. , Schönhusen U. 
Published: December 2004

Push‐pull‐Butadienes. VI. Synthesis of Substituted Nicotinonitriles2‐Aryl‐4,4‐bis(methylthio)‐1,3‐butadiene‐1,1‐dicarbonitriles 1 react with N‐bromosuccinimide or sulphuryl chloride to give 3‐bromo‐ and 3‐chloro‐butadienedicarbonitriles 3, respectively. Compounds 1 or 3 can be converted with methanethiol in alkaline solution to 4‐aryl‐2,6‐bis(methylthio)nicotinonitriles 2. Butadienedicarbonitriles 3 and sodium alkoxide yield alkoxynicotinonitriles 5. 4‐Aryl‐2,6‐dibromo‐ and 2‐bromo‐5‐chloro‐nicotinonitriles 8, respectively, are prepared by treating 1 or 3 with bromine. Nicotinonitriles 8 react with hydrazine hydrate to yield pyrazolo[3,4‐b]pyridines 12. Treatment of butadienedicarbonitriles 3 with sulphuryl chloride gives 2‐aryl‐3‐bromo‐ and 3‐chloro‐4‐chloromethylthio‐4‐methylthio‐1,3‐butadiene‐1,1‐dicarbonitriles 17, respectively. The structures of the prepared compounds are in agreement with spectroscopic data.
Synthese von B1‐substituierten Peptidyl‐Insulinen
Authors: Losse Günter , Raddatz Heike 
Published: December 2004

Synthesis of B1 Substituted Peptidyl InsulinsThe peptide derivatives Boc‐Leu‐Tyr(Bzl)‐Gln‐Leu‐OHNomenklatur und Abkürzungen nach den Regeln der IUPAC‐IUP‐Commission on Biochemical Nomenclature: Hoppe‐Seyler's Z. Physiol. Chem. 348 (1967) 256 und J. Biol. Chem. 247 (1972) 977. magnified image

of the sequence section 13–16 of the insulin A chain and Boc‐Leu‐Tyr(Bzl)‐Leu‐Val‐Cys(SEt)‐Gly‐OH corresponding to the partial sequence 15–20 of the B chain are condensated with A1, B29‐Boc
2
‐insulin via their pentachlorphenylesters. After removal of the protecting groups by HBr/TFA in the presence of anisole and ethylmercaptan the corresponding insulins elongated in position B1 are isolated and characterized by HPLC.
Intramolekulare 1,3‐dipolare Cycloadditionen von Arylaziden mit Alkinylsubstituenten
Authors: Rudorf W.‐D. , Janietz D. 
Published: December 2004

Intramolecular 1,3‐Dipolar Cycloadditions of Aryl Azides with Alkynyl SubstituentsReaction of substituted 4‐chlorobut‐2‐ynes 1 with 2‐acetaminophenol and 2‐aminothiophenol, respectively, leads to the corresponding ethers and thioethers 3 that can be converted into the alkynyl substituted aryl azides 4 by diazotation and reaction with sodium azide. Intramolecular 1,3‐dipolar cycloaddition yields 4H‐[1,2,3]triazolo [5,1‐c] [1,4] benzoxazines and benzothiazines 5. In the same way 1,4‐bis(2‐acetaminophenoxy)but‐2‐yne 6 reacts to a 3‐(2‐azidophenoxy‐methyl)‐triazolobenzoxazine 9. Its thermal decomposition gives the azomethine 11.
Fluoreszenzlöschung aromatischer Verbindungen durch Diazoniumkationen in wäßrigen Lösungen von Natriumpolyvinysulfat
Authors: Becker H. G. O. , Schütz R. , Kuzmin M. G. , Soboleva I. V. 
Published: December 2004

Quenching of Fluorescence of Aromatic Compounds by Diazonium Cations in Aqueous Solutions of PolyelectrolytesThe absorption and fluorescence spectra, and lifetimes of sodiumpyrene‐3‐sulfonate, N‐phenylacridone and acridizinium perchlorate have been measured in the absence and in the presence of sodiumpolyvinylsulfate. A study is made of the quenching by diazonium ions of the fluorescence of the aromatic compounds. The results of Stern‐Volmer plots are discussed by a micro‐heterogeneous model and compared with results in homogeneous solutions. It is suggested that contributions of quencher and aromatic compound in both polyelectrolyte and aqueous phases are important.
Sulphur Analogues of Deoxyvasicinone
Authors: Dunn A. D. , Norrie R. 
Published: December 2004

AbstractThe synthesis of the 2‐thioanalogue of deoxyvasicinone (1) 5 and some higher analogues 6 and 7 are described. Oxidation of these heterocycles with 3‐chloroperoxybenzoic acid gave the sulphoxides 12, 13 and 14 which underwent facile Pummerer rearrangement to yield, after deacetylation, the alkanols 18, 19 and 20. Under more vigorous oxidising conditions 5 and 6 were oxidatively ring opened to yield the sulphonic acids 21 and 22 whereas 7 gave the sulphone 23.
Untersuchungen zur Iodierung von 4‐Amino‐2,6‐dimethyl‐pyrimidinen – eine Möglichkeit zur regiospezifischen Funktionalisierung
Authors: Niclas H.‐J. , Zeuner F. , Gründemann E. , Zölch L. 
Published: December 2004

Studies on the Iodination of 4‐Amino‐2,6‐dimethylpyrimidine — A Possibility of the Regiospecific FunctionalizationThe iodination of 4‐amino‐2,6‐dimethyl‐pyrimidine 1a with I2/H2SO4/H2O/H2O2 does not give, as supposed hitherto, the 5‐iodo derivative (2) but affords the corresponding 2‐iodomethyl derivative 3a. The reaction pathway of the iodination is discussed. The reaction of 3a with nucleophiles leads to a variety of side chain‐substituted pyrimidines 5a–j.
Kinetics and regioselectivity of the Autoxidation of o‐Substituted Isopropyl Aromatics
Authors: Heinze Antje , Lauterbach Gerlinde , Pritzkow Wilhelm , Schmidt‐renner Wolfgang , Voerckel Volkmar , Zewegsuren Nansadyn 
Published: December 2004

AbstractThe relative chain propagation constants and the regioselectivities of the oxidations of o‐cymene and 2‐isopropyl‐1,4‐dimethylbenzene were determined by competitive oxidations of the hydrocarbons with cumene. As expected, the reactivity of the tertiary CH bond of the isopropyl group is considerably decreased by o‐methyl groups.Also in α‐isopropylnaphthalene a considerable decrease in the reactivity of the tertiary CH bond takes place.The decrease of the chain propagation constants effects a decrease of the oxidabilities of o‐substituted isopropyl aromatics. In the case of the methyl isopropyl benzenes the increase of the chain termination constants by primary peroxy radicals must also be taken into consideration. This results in a decrease of the oxidabilities which can be observed even in p‐cymene (in comparison with cumene).
Azomethinfarbstoffe ‐ Sensibilisatoren, Löscher und Reaktionspartner für Singulettsauerstoff
Authors: Grossmann N. , Winnig B. , Weise A. , Fanghänel E. 
Published: December 2004

Azomethine Dyes — Sensitizers, Quenchers and Reaction Partner for Singlet OxygenAzomethine dyes show photofading in photographic materials, possibly due to oxidation by singlet oxygen. The azomethine dyes 1a–h, 2a–h, 3c, d, f are inefficient photosensitizers of singlet oxygen formation. In tetrachloromethane the quantum yield ϕ1O2 is in the range between 8 · 10−4 and 4 · 10−3.Contrary to the literature we found that azomethine dyes react with 1O2 (kr). The reaction constants were measured by a competetive technique using 9, 10‐diphenyl anthracene and methylene blue as 1O2 sensitizer. The values of kr show that the reaction of the dyes with 1O2 can not be ignored. Besides this reaction, 1O2 is also quenched by the dyes (kq). The values of kq point to quenching of 1O2 by the tertiary amino group of the dyes via a CT‐mechanism. This study shows that in photofading of azomethine dyes the oxydation by 1O2 must be taken into consideration.
The influence of cation complexation in NaClO3 and KClO3 by crown ethers on the electronic structure of salts studied by 35Cl‐N.Q.R. method
Authors: Nogaj B. , Schroeder G. , Maćkowiak M. 
Published: December 2004

AbstractMe⊕ (Me = Na; K) cations in MeClO3 chlorates were complexed by crown ethers (CE): 12C4, 15C5 and 18C6 in solution. In the solid phase we could obtain only Na(15C5)ClO3 and K(18C6)ClO3 complexes significant shift in 35Cl‐n.q.r. frequency with respect to the frequency of pure sodium and potassium chlorates was observed. The shifts at 77K were –2.879 MHz for Na(15C5)ClO3 and –1.004 for K (18C6)ClO3.For other reaction mixtures the 35Cl‐n.q.r. frequencies observed were the same as for the appropriate pure chlorates which confirmed that the expected complexation in the solid phase had not occurred. The investigation described in this paper proved a rapid increase in selectivity of crown ethers at the transition from the solution to the solid state. Moreover, in the solid phase of Me(CE)ClO3 complexes a significant increase was found in the shielding effect of the Me⊕ cation by the surrounding crown ether.
On the Estimation of the Partial Quantum Yields for phytochrome photoconversion by a nonlinear least‐squares method
Authors: Hermann G. , Mueller Eberhard , Hermann Martin , Ullmann Thomas 
Published: December 2004

AbstractA nonlinear least‐squares method is presented which enables the estimation of the partial quantum yields of a photoreversible two component system by fitting the corresponding kinetic equation directly to experimentally measured data.The principles of this method are discussed with reference to the photochromic transformation of phytochrome as an adequate model. It is demonstrated that this method yields sufficiently accurate and highly reliable results.In addition, the advantage of the nonlinear least‐squares method when compared with the so‐called formal integration method and with the initial rate approach is emphasized.
Über die Katalyse der PRILEŽAEV‐Reaktion
Authors: Schnurpfeil D. 
Published: December 2004

About the Catalysis of the PRILEŽAEV ReactionIt is shown that a catalysis of the PRILEŽAEV reaction exists. We investigated the influence of homogeneous molybdenum catalysts on the epoxidation reaction of olefins with percarboxylic acids kinetically. The second order reaction rate data show that the MoO2(acac)2 catalyzed cyclohexene epoxidation with peracetic acid runs two times faster than the uncatalyzed reaction and the same epoxidation of oct‐1‐ene runs 15 to 30 times faster. In the same way the reduction of activation parameters in the catalytic reaction proves the catalytic effect. An influence of catalyst concentration and a formation period at the beginning of the catalytic reaction were observed. The influence of the structure of olefin and of the kind of catalyst were investigated and discussed. A formulation of the transition state is given and discussed in relation to the uncatalyzed PRILEŽAEV reaction and to the Halcon reaction.
Zur Anwendung der NMR‐Verschiebungsreagenztechnik bei Substanzen mit zwei unterschiedlichen Assoziationszentren
Authors: Radeglia R. , Zepter R. , Wentzke M. 
Published: December 2004

On the Application of the N.M.R. Shift Reagent Technique to Substances with Two Different Association SitesThe competition of two potential association sites of the same substrate molecule for the shift reagent is described by a simple association model. The relative equilibrium constants are determined by the dependence of the induced shifts observed on the amount of the added shift reagent. An example of 3.17‐bifunctionalized steroids demonstrates the applicability of the method.
Dreikomponentenreaktionen. XVII. Endständig reaktive Oligooxyethylenstrukturen aus Alkenen, Chlor und O‐Nucleophilen und deren Umsetzung zu Oxathiaalkanen
Authors: Beger J. , Pöschmann C. , Shabanov A. L. , Gurbanov P. A. 
Published: December 2004

Three Component Reactions. XVII. Terminal Reactive Oligooxyethylene Structures from Alkenes, Chlorine and O‐Nucleophiles and Their Transformation into OxathiaalkanesThe reaction of alkenes, chlorine and oxirane, dioxane, ethyleneglycole, oligoethylenglycoles, the monoethers of oligoethyleneglycoles, ethylene chlorohydrine or α‐hydro‐ω‐chloro‐oligooxyethylenes leads to compounds 6‐‐9, which contain mono or oligoether functions and one or two reactive terminal chlorine atoms. Oxathiaalkanes (10 and 12) were obtained in the reaction of such compounds with sodium mercaptides.
Untersuchungen zur Tautomerie von o,o'‐Dihydroxy‐azofarbstoffen der Eriochrom‐Reihe
Authors: Sagaster Hans‐Rainer , Röbisch Gerhard , Mehlhorn Achim 
Published: December 2004

Investigations on the Tautomerism of o,o'‐Dihydroxy Azo Dyes of the Eriochrome TypeInvestigation of the u.v.‐vis‐, 1H‐ and 13C‐n.m.r. spectra of the title substances and the isomers 3 and 3p at different pH‐values and in different solvent mixtures as well as of O,O'‐dimethyl derivatives of 2 and 3 show that in aqueous solution as well the monoanions as the trianions exist in the azo forms only. The dianions exist in dependence on the solvents as mixtures of tautomers. The results of PPP calculations for different prototropic structures are in good accordance with the experimental results.
Molecular Complexes of Cyclophanes. XIV. Charge‐transfer complexes of polynuclear[2.2] paracyclophanes with π‐acceptors
Authors: Mourad Aboul‐Fetouh E. , Akkermann‐Kubillus Anja , Hucker Joachim 
Published: December 2004

AbstractThe charge‐transfer (CT) spectra of the π‐complexes formed by several π‐acceptors with some polynuclear[2.2]paracyclophanes have been measured. Comparison of these CT complexes with those of model compounds supports the existence of the transannular electronic interactions in the paracyclophane nucleus. The infrared spectra of a number of CT complexes reveal the increase of the electron density on the π‐acceptor molecule in the CT complexes. Some crystalline CT complexes were prepared and analysed.
Protonierung und Solvatation schwacher organischer Basen. IV. H‐NMR‐spektroskopische Bestimmung der Basizität aliphatischer Ketone
Authors: Roth H. , Freiberg W. , Kröger C.‐F. 
Published: December 2004

Protonation and Solvation of Weak Organic Bases. IV. 1H‐N.M.R. Spectroscopic Determination of the Basicity of Aliphatic KetonesFrom protonation ratios for a series of methyl and ethyl alkyl ketones 1—13 with gradually branched alkyl groups in the H2O–H2SO4 system, determined by 1H‐n.m.r. spectroscopy, basicity and solvation parameters are systematically estimated by application of extrapolation procedures based on the Hammett acidity function H0 or the excess acidity X.
Revisitation of Formaldehyde Aniline Condensation. VIII. Monomeric N‐methylene anilines
Authors: Giumanini Angelo G. , Verardo Giancarlo , Poiana Marco 
Published: December 2004

AbstractA convenient, high yield “dry” method of synthesis of monomeric N‐methyleneanilines (6a—i) and the characterization of the products by m.s., 1H‐ and 13C‐n.m.r. and i.r. are reported, improving previous procedures and describing new compounds. It appeared that the existence of monomeric N‐methyleneanilines is strictly related to the presence of enough steric hindrance to oligomerization by substituents in ortho positions. Moreover, some addition products of formaldehyde to an amine and its corresponding imines are tentatively identified on the basis of the observed mass spectrum of the whole reaction mixture.The reaction products of formaldehyde with 2,6‐dimethylaniline (1a) provided an example of a mobile equilibrium between monomeric and trimeric imine.
Reaktionen unter Beteiligung von Ylid‐Zwischenstufen. III. Zur Darstellung und Konfigurationsanalyse spirokondensierter Tetrahydroindolizine
Authors: Thurner J.‐U. , Richter W. , Köppel H. , Tomaschewski G. , Hauser A. , Van Binst G. 
Published: December 2004

Reactions by Participating of Ylide‐Intermediates. III. On Preparation and Structural Elucidation of Spiro‐condensed TetrahydroindolizinesN‐(Fluroen‐9‐yl)‐pyridinium‐ and ‐isoquinolinium ylides (5) to (8) react with electrondeficit olefinic dipolarophiles under mild conditiones to give satisfactory to good yields of the corresponding spirocondensated tetrahydroindolizines (10) to (13). The structure and configuration of all isolated products were elucidated by spectroscopical methods, especially by 1 D‐ and 2 D 1H‐n.m.r. The 1.3‐dipolar cycloaddition produced regiospecific cycloadducts. From the observed regiospecifity of unsymmetrically substituted olefines (9) can be concluded that the cycloaddition is HOMO(1.3‐dipole) — LUMO(dipolarophile) controlled. The olefines (9) add stereospecifically under retention of their configuration via exo as well as endo transition states. The nitrosubstituted ylides (6) and (8) produced always mixtures of diastereomeric cycloadducts (11) and (13).
Cyclofunktionalisierung von 2‐Allyl‐phenolen mit Schwefelchloriden. 2‐Arylthiomethyl‐2,3‐dihydrobenzofurane aus 2‐Allyl‐ und 2‐Methallyl‐phenolen und Arylsulfenylchloriden
Authors: Mühlstädt M. , Meinhold H. , Muslih R. M. 
Published: December 2004

Cyclofunctionalization of 2‐Allyl‐phenols with Sulfur Chlorides: Synthesis of 2‐Arylthiomethyl‐2,3‐dihydrobenzofurans by Reaction of 2‐Allyl‐ and 2‐Methallyl‐phenols, Respectively, and Arylsulfenyl ChloridesReactions of acetylamino substituted 2‐allyl‐phenols (1 and 2), and 2‐methallyl‐phenol (6), respectively, with different arylsulfenyl chlorides (3a—d) yield the products of a cyclofunctionalization 5‐ or 7‐acetylamino‐2‐arylthiomethyl‐2,3‐dihydrobenzofurans (4a–d) or (5a–d) and 7‐acetylamino‐2‐arylthiomethyl‐2‐methyl‐2,3‐dihydrobenzofurans (7a–d). The compounds 7 are the first examples of cyclofunctionalization of 2‐methallylphenols by means of sulfur chlorides. The identification of the products was carried out by mass spectrometry, 1H‐n.m.r. spectroscopy and elemental analysis.
Zur Reaktion von N‐(N′,N′‐Dialkyl(aryl)amino‐thiocarbonyl)benzimidoylchloriden mit Kaliumthiocyanat
Authors: Weber G. , Hartung J. , Beyer L. 
Published: December 2004

Reactions of N‐(N′,N′‐Dialkyl(aryl)amino‐thiocarbonyl)benzimidoylchlorides with Potassium ThiocyanateThe treatment of the title compound N‐(amino‐thiocarbonyl)‐benzimidoylchloride 1 with potassium thiocyanate leads in dependence on the solvents (methanol, acetic acid, acetone) either to the 1,3,5‐thiadiazine‐2‐thione 2a–d or to the ring opened isothiocyanate 4a, b. In the case of methanol the N‐(amino‐thiocarbonyl)benzimidates were formed as by‐products.The structure of the products is confirmed by analytical data and by chemical transformations. 2a reacts with methyl iodide to form the 2‐methylthio‐6‐morpholino‐4‐phenyl‐1,3,5‐thiadiaziniumiodide 3a. From 4a and water the N‐(morpholino‐thiocarbonyl)benzamide 5a arises. The reaction of morpholine with 4a yields the benzamidine 6a.
Polycarbonyl heterocycles. VI. A 13C‐N.M.R. study on the structure of H‐bonded ion pair: 3‐Benzoyl‐pyrrolidine Derivatives/Piperidine
Authors: Zaleska Barbara 
Published: December 2004

AbstractComparison of spectral data obtained from 13C n.m.r. analyses for compound 1–6 implies the structure of H‐bonded ion pairs 2, 4, 6. In the formation of ion pair 2 the exo‐enol tautomeric form “b” is involved, on the other hand, the endoenolic form “c” is a main tautomer producing the H‐bonded ion pair 4. A stereospecific transformation of compound 5 leads to formation of complex 6 with aliphatic amine.
Änderung der Lichtabsorption von 4′‐Diethylamino‐α‐cyanostilben‐4‐diazoniumionen durch Komplexbildung mit Ethylenglycolderivaten, Kronenethern und Valinomycin
Authors: Walkow F. 
Published: December 2004

Colour Change of 4‐Diethylamino‐α‐cyano‐stilbene‐4‐diazonium Ions by Complex Formation with Ethylenglycol Derivatives, Crownethers and ValinomycineThe formation and light absorption of complexes consisting of coloured stilbene‐4‐diazonium ions and different ethylenglycoles, crownethers and valinomycine were investigated. On complex formation the longest wavelength absorption band of the diazonium compounds shifts hypsochromically. This hypsochromism is solvent dependent. The difference between the absorption maximum of a free and complexed diazonium ion increases with increasing polarity and decreasing n‐donicity of the solvents. Other complex forming cations are able to replace the diazonium ions in the complexes, whereby the colours of the original diazonium ions are regenerated. These colour changes can be used to indicate the ability of n‐donor compounds to act as an ionophore.
An improved synthesis of (24R)‐3β‐(2H‐Tetrahydropyran‐2‐yloxy)cholesta‐5,7‐diene‐24,25‐diol – a key intermediate in the synthesis of (24R)‐24,25‐dihydroxyvitamin D3
Authors: Schrötter E. , Landmann Elfi , Schick H. , Schönecker B. , Hauschild U. , Droescher P. 
Published: December 2004

AbstractA multistep procedure for the conversion of ergosterol into the tetrahydropyranyl ether of (24R)‐24,25‐dihydroxyprovitamin D3 using 1,4‐dihydrophthalazine‐1,4‐dione as diene protecting agent was compared with an established route, which uses 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione for the protection of the diene system. The disclosed reaction sequence allows to double the overall yield. The 1,4‐dioxo‐1,2,3,4‐tetrahydrophthalazin‐2,3‐ylene group proved to be the better diene protecting group in the ozonolytic degradation of the ergosterol side chain. Maintaining the protecting group in the next reaction steps offered further advantages by diminishing the air and light sensitivity of the intermediates.