bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of two new corticotrophic peptides containing homoarginine in position 8
Authors: Tesser G. I. , Pleumekers A. W. J. , Bassie W. , Balvert‐Geers I. C. 
Published: September 2010

AbstractThe octadecapeptide amide I and the tetracosapeptide II containing homoarginine in position 8 have been synthesized according to a generally approved scheme. As a new feature, the hydroxyl functions of the serine and tyrosine residues were protected in the synthesis of the N‐terminal decapeptide. The latter, presumably by its higher solubility in organic solvents, afforded the protected end products in an improved yield. For complete deprotection, however, acid‐treatment of these compounds had to be extended over longer periods than in the absence of the ether functions.
“Investigation of the angular dependency of Co‐O‐Co superexchange by means of magnetic susceptibility measurements in dilute systems”
Authors: van Leeuwen G. C. M. 
Published: September 2010

AbstractMagnetic susceptibility measurements in the temperature range of 4 to 150°K have been performed on samples of CoxMg1‐x O, x ranging from 2.5% to 5% and on LiMg1‐xCoxPo4, x ranging from 1.5% to 5%. Deviations from the single ion susceptibility have been observed for all samples and explained by taking into account an effective exchange interaction 2JsTi. STj between ions within various types of isolated clusters, s being the fictitious spin of the doublet ground state.From the experimental data on CoxMg1‐xO for J(90°)/k and J(180°)/k the values 5.0 °± 0.3°K and 135 ± 10°K have been derived, while in LiMg1‐xCoxPO4 J(132°)/k has been found equal to 12 ± 4°K.
The conjugate addition of methyl Grignard reagents to 5α‐1‐estren‐3‐ones
Authors: Bolt C. C. , Zeelen F. J. 
Published: September 2010

AbstractThe conjugate addition of methyl Grignard reagents to 5α‐1‐estren‐3‐ones leads to 1α‐methyl derivatives. It is suspected that this is due to formation of a half chair conformation of ring A upon 1α attack, whereas 1β‐attack would yield a product having a half boat conformation of ring A.
Synthesis and thermal decomposition of tertiary β‐nitroalkyl peroxynitrates
Authors: Duynstee E. F. J. , Hennekens J. L. J. P. , Housmans J. G. H. M. , van Raayen W. , Voskuil W. 
Published: September 2010

AbstractThree tertiary β‐nitroalkyl peroxynitrates 2a, 2b and 2c were prepared by reaction of N2O4 and excess O2 with isobutene (la), 2,3,3‐trimethyl‐2‐butene (1b) and 2,3‐dimethyl‐2‐butene (1c), respectively. These compounds are rather unstable and at 23° slow decomposition occurs. It seems likely that this decomposition starts by O‐O bond fission yielding an NO3 radical and a β‐nitroalkoxy radical. In the case of 2a this alkoxy radical either reacts with NO2 or dimerises but no β‐fission is observed. In the case of 2b and 2c extensive β‐fission of the alkoxy radical produces alkyl radicals which react with NO3 radical forming alkyl nitrate or react with O2 and NO2 (produced from NO3) forming alkyl peroxynitrate.
Chemistry of cyclopropene IV. The formation of cycloprop‐1‐enylcarbinols
Authors: Schipperijn A. J. , Smael P. 
Published: September 2010

AbstractA relatively simple method has been developed for the preparation of (cycloprop‐1‐enyl)methylcarbinols from 1‐sodiocyclopropene and epoxides. Satisfactory yields are obtained only with epoxides having at least one unsubstituted epoxy carbon atom.In addition, a method is given for the synthesis of cycloprop‐1‐enylcarbinols from 1‐sodiocyclopropene and ketones. Its applicability is limited by the tendency of the products to polymerize and is restricted to those ketones which have at least one alkyl substituent at each of the carbon atoms adjacent to the carbonyl group. Aldehydes fail to give the corresponding carbinols.
Some aspects of the solution photochemistry of 1,3‐cyclohexadiene, (Z)‐ and (E)‐1,3,5‐hexatriene
Authors: Minnaard N. G. , Havinga E. 
Published: September 2010

AbstractUV irradiation (λ = 265 nm) of 1,3‐cyclohexadiene yields (Z)‐1,3,5‐hexatriene with good efficiency (Φ = 0.41). UV irradiation also effects equilibration between (Z)‐ and (E)‐isomers, be it with rather low quantum yields (ΦZ→E = 0.034; ΦZ→E =0.016). The Z ⇄ E isomerization can be sensitized by triplet sensitizers, e.g. biacetyl. This reaction occurred also upon irradiation of solutions in bromoform with light of 436 nm (So → T absorption).A simple formula for the calculation of quantum yields from composition data is given.
Chemistry of acetylenic ethers 102: Reaction of di(1‐alkynyl) sulfides with sodium sulfide, selenide and telluride. Formation of 1,4‐dithiins, 1,4‐thiaselenins and 1,4‐thiatellurins
Authors: Meijer J. , Vermeer P. , Verkruijsse H. D. , Brandsma L. 
Published: September 2010

AbstractInteraction between di(1‐alkynyl) sulfides (1) and sodium sulfide, selenide or telluride in mixtures of liquid ammonia and methanol or dimethylformamide and methanol gives 1,4‐dithiins (2), 1,4‐thiaselenins (3) and 1,4‐thiatellurins (4).
Benzoheterocyclic synthesis via benzoannelation of heterocyclic ortho‐dicarboxaldehydes: Benzimidazoles from an imidazole‐4,5‐dicarboxaldehyde; a benzo[b]furan from a furan‐2,3‐dicarboxaldehyde
Authors: Corvers A. , de Groot Ae. , Godefroi E. F. 
Published: September 2010

AbstractThe base‐catalyzed condensation of an imidazole‐4,5‐dicarboxaldehyde, 1, with sulfides (ZCH2)2S (Z = an electronegative group) is shown to constitute a general route to 5,6‐disubstituted benzimidazoles. In one case, a sulfoxide, (CH3OOCCH2)2SO, behaves similarly. Sulfones (ZCH2)2SO2 bring about the transformation of 1 into imidazo[4,5‐d]thiepin‐6,6‐dioxides; these are stable compounds, losing SO2 only at elevated temperatures with formation of benzimidazoles. The general applicability of this benzoannelation route is further illustrated by the conversion of furan‐2,3‐dialdehyde, 9, to benzo[b]furan, 10.
Mass spectrometry of products obtained by reduction of 6‐nitroquinaldine and 2‐nitrophenanthrene with phosphine
Authors: Leclercq P. A. , Bellaart A. C. , van de Ven L. J. M. 
Published: September 2010

AbstractReduction of 6‐nitroquinaldine and of 2‐nitrophenanthrene was carried out with phosphine under conditions described by BucklerS. A. Buckler, L. Doll, F. K. Lind and M. Epstein, J. Org. Chem. 27, 794 (1962).
. Reduction of 6‐nitroquinaldine yielded 3,9‐dimethyldipyrido[3,2‐a: 3′,2′‐h]phenazine, pyridazino‐[4,3‐f: 5,6‐f′]biquinaldine‐3‐oxide and 6,6′‐azoquinaldine, while 2‐nitrophenanthrene afforded only 2,2′‐azoxyphenanthrene. Reduction of pyridazino[4,3‐f: 5,6‐f′]biquinaldine‐3‐oxide with zinc dust and sodium hydroxide yielded 6,6′‐diamino‐5,5′‐biquinaldyl, which was converted into 6,6′‐di(acetylamino)‐5,5′‐biquinaldyl. The structures were verified by spectrometry. Mass spectra of the new compounds are discussed.
Thermal and photoinduced deboronations of some pyridine‐ and benzeneboronate anions
Authors: Fischer F.C. , Havinga E. 
Published: September 2010

AbstractDissociation constants of 3‐ and 4‐pyridineboronic acid and σ‐values for the meta‐ and para‐B(OH)2 and ‐B(OH)3− groups have been determined; in aqueous solutions the compounds occur predominantly in the pyridiniumboronate form. 2‐Pyridineboronate seems to be thermally unstable, whereas 3‐ and 4‐pyridineboronic acids are thermally stable but decompose upon treatment with methyl iodide.Irradiation in neutral or slightly basic solution of 3‐ and 4‐pyridineboronic acids effects splitting into borate and pyridine (in its turn photochemically converted into “photopyridine”).We suggest that these thermal and photoreactions may be considered as SE l‐protodeboronations of the pyridinium boronate form. Experimental reactivities could be roughly correlated with results of P.P.P. calculations of the change of electrostatic energy between initial and transition state.
Halogen migration and amination in reactions of halogeno derivatives of five‐membered hetarenes with potassium amide in liquid ammonia
Authors: van der Plas H. C. , de Bie D. A. , Geurtsen G. , Reinecke M. G. , Adickes H. Wayne 
Published: September 2010

AbstractOn treatment of 2‐bromothiophene, 2,3‐, 2,4‐, and 2,5‐dibromothiophene with potassium amide in liquid ammonia at − 75°, a bromine migration of position α to position β of the thiophene ring takes place. On treatment of the above mentioned compounds with potassium amide in liquid ammonia at − 33°, besides α to β bromine rearrangement, amination to 3‐aminothiophene was observed.The mechanism of the transbromination is assumed to be an intermolecular process, involving dibromo‐ and tribromo‐thiophenes. The formation of 3‐aminothiophene does not occur via a didehydro intermediate, but it is the result of amination of a polybromothiophene, yielding an amino‐bromothiophene, which is debrominated by reaction with amide ion or a thiophene anion.
Stereochemical aspects in mass spectrometry: Comparison of the mass spectra of some (E)‐ and (Z)‐ionone and ‐ionol derivatives
Authors: van Wageningen A. , Cerfontain H. , Nibbering N. M. M. 
Published: September 2010

AbstractThe mass spectra of the (E)‐ionones and (E)‐ionols are markedly different from those of the corresponding (Z)‐isomers. The differences are explained ‐ using the concept of charge localization in terms of the difference in ability of the molecular ions of a given pair of geometrical isomers to undergo intramolecular ring closure and intramolecular hydrogen transfer reactions. The mass spectral difference of a given pair of geometrical isomers can be used for the configurational assignment of the two isomers.
Étude conductimétrique de la réaction de NOCl sur SO3 dans SO2 liquide à −20°C
Authors: de Jaeger R. , Heubel J. 
Published: September 2010

AbstractFrom a conductimetric study of the effect of NOCl on SO3 in SO2 at − 20°C the compounds NO(SO3)nCl in which n = 1,2,3 have been isolated and the probability of the presence of much more condensed terms (n = 4,5,6) indicated.The solubility of NOSO3Cl and NOS2O6Cl in SO2 at −20°C has been determined and it has been demonstrated, by the variations of the equivalent conductivity in terms of 1/√c, that the behaviour of NOSO3Cl in SO2 resembles that of a weak electrolyte.
Proton magnetic resonance studies of specifically deuterated cyclohexane compounds. Part IV. 1,1‐Dimethylcyclohexane, 1,3‐ and 1,4‐di‐t‐butylcyclohexane (cis and trans), and cis,cis‐1,3,5‐tri‐t‐butylcyclohexane
Authors: Remijnse J. D. , van Bekkum H. , Wepster B. M. 
Published: September 2010

AbstractThis paper describes the preparation and a PMR investigation of a series of deuterium derivatives of 1,1‐dimethylcyclohexane, cis‐ and trans‐1,3‐ and 1,4‐di‐t‐butylcyclohexane, and cis,cis‐1,3,5‐tri‐t‐butylcyclohexane. Accurate PMR parameters are obtained by the application of deuterium decoupling and computer simulation and iteration of the spectra. The coupling constants in trans‐1,4‐di‐t‐butylcyclohexane show that the t‐butyl sides of the ring are puckered to the same extent as in t‐butylcyclohexane. In cis‐1,3‐di‐t‐butylcyclohexane and cis,cis‐1,3,5‐tri‐t‐butylcyclohexané the axial protons at the carbon atoms between the t‐butyl groups are also bent towards the centre of the ring. The axial methyl group in 1,1‐dimethylcyclohexane is shown to cause a flattening of the ring. The chemical shifts of the ring protons provide further insight into the “anomalous” shift of 2‐axial protons in methylcyclohexane(s).The vicinal coupling constants of trans‐1,3‐di‐t‐butylcyclohexane confirm that this compound exists for the greater part in a twist conformation.
The preparation of the eight‐membered ring system (NPCl2)3NSOCl
Authors: Voswijk C. , van de Grampel J. C. 
Published: September 2010

AbstractFrom the reaction mixture of [Cl3P=N‐PCl2=N‐PCl3] + [PCl6]− and SO2(NH2)2 (molar ratio 1:1) a solid with formula (NPCl2)3NSOCl could be isolated in small yield. The IR and mass spectrum of this eight‐membered ring system are discussed.
Conformational analysis of some alkylbenzene derivatives Part III: The barriers to rotation and the preferred conformations of some hydroxy‐alkyl groups in 1‐(1‐hydroxyalkyl)‐3,4,5‐trimethoxybenzenes
Authors: Baas J. M. A. , van der Toorn J. M. , Wepster B. M. 
Published: September 2010

AbstractThe barriers to rotation about the Cal‐Car bond of six hydroxyalkyl groups in 1‐C(OH)‐R1R2‐3,4,5‐trimethoxybenzenes have been determined from the coalescence of the PMR signals for the aromatic hydrogen atoms. The coalescence temperatures (°C) and the free energies of activation (kcal/mole) measured for the groups substituted with R1 and R2 are, respectively: But, H, −96, 8.7; But, Et, −38, 11.3; But. Pr, −40, 11.3; But, Bu, −38, 11.4; But, Pri, −8, 13.0; Pri, Pri, −42, 11.2. The heights of the barriers to rotation and the preferred conformations of the hydroxyalkyl groups with respect to the plane of the benzene ring are discussed.
A comparison of properties of 3,4‐dibromo and 3,4‐dichloro derivatives of 1,6‐and 1,7‐naphthyridine
Authors: Czuba W. , Woźniak M. 
Published: September 2010

AbstractDifferences have been found in the reactivity of halogens in positions 3 and 4 of 1,6‐naphthyridine. The differences were observed in the reaction of 3,4‐dihalogenonaphthyridines with p‐toluenesulfonic hydrazide. Convenient methods are described for the synthesis of 3‐bromo‐ and 3‐chloro‐1,6‐naphthyridine.
Photochemical additions of o‐quinones and benzil to conjugated alkenynes
Authors: Koster R. J. C. , Streefkerk D. G. , Oudshoorn‐van Veen J. , Bos H. J. T. 
Published: September 2010

AbstractPhenanthraquinone (PQ) and tetrachloro‐o‐benzoquinone were added photochemically to the double bond of various substituted alkenynes (1), yielding dihydrodioxin derivatives (2, 5); in some cases oxetane derivatives (4) were isolated too. Generally the photochemical addition occurred non‐stereospecifically. Reversible additions of PQ to the double bond were established. Thermal additions of tetrachloro‐o‐benzoquinone occurred with retention of configuration. The photochemical addition of benzil to conjugated alkenynes and to alkenes, however, led to oxetanes (6) only.
Kinetics of water‐ammonia exchange in the series of aquaamminecobalt(III) complexes. IV. Rates of interconversion reactions between the tetraammine and pentaammine ions
Authors: Bohte E. G. A. M. , Balt S. 
Published: September 2010

AbstractThe kinetics of base hydrolysis of the Co(NH3)5OH2+ ion have been studied as a function of pH, ammonia concentration and temperature. The reaction takes the route via outer sphere complexes of the pentaammine ion or its conjugate base. The actual process can be understood as a dissociative interchange of ammonia from the first coordination sphere and hydroxyl ions (or possibly water) from the second sphere. Also rate constants for the reverse reaction are compared with previously determined values. The conjugate base mechanism, one of the routes for the reaction of the tetraammine ion with NH3, is put on a more quantitative basis.
Cycliacylation of 3‐phenylpropanoic and 4‐phenylbutanoic acids in liquid hydrogen fluoride: Kinetics, mechanism and substituent effects
Authors: Brouwer D. M. , van Doorn J. A. , Kiffen A. A. , Kramer P. A. 
Published: September 2010

AbstractA kinetic study has been made of the cycliacylation in liquid HF of protonated 3‐phenylpropanoic and 4‐phenylbutanoic acids and a number of their alkyl derivatives to the corresponding 1‐indanones and 1‐tetralones*. The acylating species in these reactions has been shown to be the free acyl cation. Formation of this cation becomes rate‐determining at high rates of the cyclization step proper and then masks any further activation of the benzene ring. The cyclization to 1‐indanones, but not that to 1‐tetralones, exhibits an unusually large ortho partial rate factor (for methyl groups fo is as large as fp). PMR spectroscopic data indicate that replacement of the benzylic hydrogen atoms in 3‐phenylpropanoic acids by methyl groups has a great influence on the conformation around the C(2)‐C(3) bond. This results in a proximity effect that accelerates the cyclization reaction by a factor of about 102.
Didehydrohetarenes (XXXIII). Evidence for a 4,5‐didehydropyridazine in the amination of 4‐halogenopyridazines with potassium amide in liquid ammonia
Authors: Klinge D. E. , van der Plas H. C. , Koudijs A. 
Published: September 2010

Abstract4‐X‐3‐(methoxymethyl)‐6‐methylpyridazine (X = Cl, Br, I) on treatment with potassium amide in liquid ammonia at − 33°C gives a mixture of 4‐ and 5‐amino‐3‐(methoxymethyl)‐6‐methylpyridazine (ratio 1: 5), which ratio is independent of the nature of the halogen atom. A 4,5‐didehydropyridazine is proposed as intermediate.
Penta co‐ordinated organo‐phosphorus compounds as model substances for simulation of biochemical conversions. Part I. A model description for the specific interaction t‐RNA synthetase‐amino acid; a selection procedure
Authors: Voncken W. G. , Buck H. M. 
Published: September 2010

AbstractIt is demonstrated that the O‐alkylation of acids and phenols with oxaphospholenes can be used as a model system for biochemical conversions. The mechanism of the acylation of Coenzyme A and a selection procedure for amino acids by the t‐RNA synthetases are described with the aid of the model system.
Ring transformations in reactions of heterocyclic compounds with nucleophiles (VIII). Conversion of pyrimidines into isoxazoles
Authors: van der Plas H. C. , Vollering M. C. , Jongejan H. , Zuurdeeg B. 
Published: September 2010

AbstractWhen pyrimidine, 1‐methylpyrimidinium methosulfate, 1,3‐diethylpyrimidinium tetrafluoroborate or pyrimidine N‐oxide is reacted with hydroxylamine hydrochloride, isoxazole is formed in a good yield. On reaction of 4,6‐dimethylpyrimidine and its corresponding N‐oxide with the same reagent 3,5‐dimethylisoxazole is obtained. Similarly, from 6‐methyl‐4‐phenylpyrimidine 1‐oxide 3‐methyl‐5‐phenylisoxazole is formed. It has been found by 15N‐labelling experiments that the NO moiety of the isoxazole ring originates from the hydroxylamine and not from the magnified image function of the pyrimidine N‐oxide.
PMR‐studies on the formation of adducts between 4‐substituted‐5‐bromopyrimidines and potassium amide in liquid ammonia
Authors: Geerts J. P. , Rasmussen C. A. H. , van der Plas H. C. , van Veldhuizen A. 
Published: September 2010

AbstractPMR‐spectra of some 5‐bromo‐4‐R‐pyrimidines (R=Ph, But, OMe, PhMeN, MeNH, Me) in KNH2/liquid NH3 are described. Evidence is presented for the formation of stable σ‐adducts by attack of an amide ion on C6 of the pyrimidine ring in the cases of R=Ph, But, OMe, PhMeN. When the C4‐substituent contains an acidic hydrogen atom α to the aromatic nucleus (R=MeNH, Me), deprotonation occurs and in the case of R=Me also adduct formation has been observed.
Chemistry of acetylenic ethers 105. Addition of organocopper(I) reagents to 1‐alkynyl sulfoxides
Authors: Vermeer P. , Meijer J. , Eylander C. 
Published: September 2010

AbstractOrganocopper(I) reagents R1Cu add readily to l‐alkynyl sulfoxides R2CCS(O)R3 with the formation of vinylic sulfoxides R1R2CCHS(O)R3 in high yields. The addition proceeds in a stereospecific manner.
Synthesis of 1‐(methylthio)propyl propenyl disulfide and sec‐butyl 3‐(methylthio)allyl disulfide, two pesticides from asa foetida
Authors: Meijer J. , Vermeer P. 
Published: September 2010

Abstract1‐(Methylthio)propyl propenyl disulfide (IV) and sec‐butyl 3‐(methylthio)allyl disulfide (VII), isolated from Asa foetida, have been synthetisized in reasonable yields, starting from methyl dithiopropionate and 1‐(methylthio)‐3‐chloropropene respectively.
Diversity in the course of the reactions of the 4‐halogenoisoquinolines with potassium amide in liquid ammonia and with piperidine
Authors: Sanders Georgine M. , van Dijk M. , den Hertog H. J. 
Published: September 2010

AbstractThe reactions of the 4‐X‐isoquinolines (X=F, Cl, Br, I) with potassium amide in liquid ammonia were investigated. In amounts depending on the halogen present, 1‐amino‐4‐X‐isoquinoline and 1‐aminoisoquinoline are formed by a Chichibabin‐type reaction and an abnormal AE mechanism, respectively. Evidence for the intermediate tetrahedral complex in position 1 was obtained by PMR measurements on 4‐chloroisoquinoline. In the case of 4‐bromo‐ and 4‐iodoisoquinolines reduction and coupling processes occur at the same time, leading to isoquinoline, 4,4′‐biisoquinoline and 1‐amino‐4,4′‐biisoquinoline, probably via a carbanion initially formed. Abnormal substitution was also established together with the normal AE process in the reactions of 4‐chloro‐, 4‐bromo‐ and 4‐iodo‐isoquinolines with piperidine, yielding both 1‐piperidinoisoquinoline and 4‐piperidino‐isoquinoline.
The chemistry of small ring compounds. Part 28: Cyclopropyl cation stabilisation in thermolysis of some cyclopropyl ethers and sulfides
Authors: van Tilborg W. J. M. , Steinberg H. , de Boer Th. J. 
Published: September 2010

AbstractThe thermolysis of 1,1′‐disubstituted dicyclopropyl ethers with substituents AcO, OH (3a); MeO, OH (3b) and HO, OH (3c) has been studied, together with the sulfide 3d, the thioether analogue of 3c. It is found that the cyclopropyl ethers 3 easily split off cyclopropanone, which cannot be isolated as such because of rapid oligomerisation. This is accompanied by some ring‐opening to a 2‐hydroxyallyl cation, CH2C(OH)\documentclass{article}\pagestyle{empty}\begin{document}$\rm{C}^\oplus $\end{document}CH2, thus explaining the ultimate formation of substituted acetones. No evidence for the transient existence of O‐protonated cyclopropanone magnified image, isomeric with the hydroxyallyl cation, could be obtained. The sulfide 3d behaves entirely differently: on heating it gives the spirocyclic sulfur compounds 12 and 13. The formation of these products is explained in terms of d‐orbital participation of sulfur in the stabilisation of an intermediate cyclo‐propylsulfinium ion.
Cycloaddition of isothiocyanates with diazomethane and hydrazoic acid
Authors: Hoff S. , Blok A. P. 
Published: September 2010

AbstractMethyl, phenyl and 1‐alkenyl isothiocyanates 1 can react with diazomethane to give the corresponding 5‐amino‐1,2,3‐thiadiazoles 4. In the presence of an excess of diazomethane these thiadiazoles rearrange to 1‐substituted‐5‐(methylthio)‐1H‐1,2,3‐triazoles 3. Reaction of 1‐alkenyl isothiocyanate 1a with hydrazoic acid yields the corresponding 5‐(1‐alkenylamino)‐1,2,3,4‐thia‐triazole 11, which does not rearrange when treated with diazomethane.
Cycloaddition reactions involving carbon‐carbon double bonds of heteroaromatic compounds
Authors: Reinhoudt D. N. , Kouwenhoven C. G. 
Published: September 2010

AbstractThe enamine‐like character of a pyrrolidino‐substituted carbon‐carbon double bond in heteroaromatics has been demonstrated by the fact that such compounds can undergo cycloaddition reactions with 1,3‐dipolar reagents such as benzonitrile oxides, diaryl nitrilimines and electron‐deficient dienes such as 1,4‐diphenyl‐s‐tetrazine and tetrachloro‐o‐quinone. In some cases the reaction products are tautomeric mixtures of the cycloadduct and the corresponding linear (Michael) adduct. Reagents such as phenyl iso(thio)cyanate give rise to the exclusive formation of a linear Michael adduct.The mechanisms of the reactions are discussed.