bluuebunny/crossref_metadata_2025 huggingface dataset:
Petits cycles à liaison germanium‐azote: Synthèse et réactivité de germa‐2 azolidines, germa‐2 azétidines, germa‐2 aziridines. Caractérisation de germa‐imines: Nouveaux intermédiaires à germanium π‐lié
Authors: Rivière‐Baudet M. , Rivière P. , Satgé J. , Lacrampe G.
Published: September 2010

Germylated 3‐, 4‐ or 5‐membered heterocycles containing a Ge‐N bond are synthetized by direct aminolysis (followed by dehydrochlorination) or by action of amino dilithium compounds on germylated dichlorides of the general structure magnified image. The preparations of these new dichlorides are also described.

2‐Germaazolidines are thermally stable. 2‐Germaazétidines decompose at moderate temperature, through a β‐elimination process, to give germa‐imine magnified image and alkene. 2‐Germaaziridines, likely in equilibrium with an open zwitter ionic form, readily decompose through an α‐elimination process, to lead to the corresponding germylene and imine.

The reactivity of these heterocycles has been considered from specific reactions of the Ge‐N bond: cleavage by protic species, LiAlH4 reduction or addition on insaturated compounds (CS2, PhNCO), the last reaction leading to ring expansion.
N,N‐Dimethyl‐2,4,6‐tri‐tert‐butylaniline: Preparation and properties
Authors: Harff G. A. , Sinnema A. , Wepster B. M.
Published: September 2010

The title compound, 3, is prepared in high yield starting from 2,4,6‐tri‐tert‐butylaniline, 1. Reaction with formaldehyde provides N‐methylene‐2,4,6‐tri‐tert‐butylaniline, 5; N‐methylation then gives the immonium salt 6 which is reduced to 3. The thermodynamic dissociation constant in 50% ethanol at 25°C, pKa* = ‐ 1.42, is 5.6 pK units lower than that of N,N‐dimethylaniline. The effects contributing to this difference are evaluated. Protonated 3 is found to have a rotational barrier around CarN, of 63.6 kJ/mol, which is about 4.5 kJ/mol lower than that found for protonated N,N‐dimethyl‐2,4,6‐trimethylaniline.
Investigations on sterols. 40. The synthesis of ring D substituted 9β,10α‐steroids
Authors: Halkes S. J. , van Etten A. B. , Postmus T. L. , Bontekoe J. S. , Rappoldt M. P.
Published: September 2010

The retro configuration (9β,10α) was introduced into pregnane derivatives containing substituents at C(16) and/or C(17) by irradiation of a suitable 5,7‐diene. In this way the title compounds became much more accessible than by the introduction of ring D substituents into 20‐ketoretro‐steroids.
Conductivity and relaxation effect of alkali polymethacrylates in alkali bromide solutions
Authors: van der Drift W. P. J. T. , Overbeek J. Th. G.
Published: September 2010

The electric conductivity of alkali polymethacrylates in aqueous solutions of alkali bromides with concentrations varying from 0.001 mol/l to 0.1 mol/l was measured. From a comparison of the conductivities of different alkali salts (Li, Na, K) the relaxation correction on the mobility of the polyion and of the counterions was estimated by use of the method of Möller et al. This correction lowered the mobilities by a factor of about one half. Relaxation effects of similar magnitude have been derived from the dispersion of the conductivity of other linear polyelectrolytes in the megacycle range.
A magnetic resonance study on the Mn(II)‐poly(methacrylic acid) interaction
Authors: Westra S. W. T. , Leyte J. C.
Published: September 2010

The interaction of Mn2+ with poly(methacrylic acid) in aqueous solutions is studied as a function of the polymer charge density using 1H‐nuclear magnetic relaxation data, Mn2+ X‐band ESR spectra and IR spectra of the polymer carboxylate groups. A model comprising at least two phases (associated and free Mn2+ ions) is necessary for a consistent interpretation of the experimental results. As no evidence for direct site binding was found, the metal ions are considered to be hydrated and mobile in both phases. In the associated phase the interaction with the charged macromolecule is seen to reduce the mobility of the fully hydrated Mn2+ ions with respect to the free, unperturbed ions.

The results obtained here are compared with an earlier study of the interaction of Mn2+ with poly(acrylic acid) a polymer that is similar to poly(methacrylic acid) in many respects. If both polymers bear sufficient charge, their influence on the Mn2+ ions in the associated phase is not too different. In the region of low polymer density, where densely coiled conformations prevail for poly(methacrylic acid) a dramatic reduction of the mobility of the metal ions contrasts sharply with the moderate influence of poly(acrylic acid).
Substituted imidazoles as ligands for copper(I) and copper(II). Stabilisation of copper(I) in case of bulky substituents
Authors: Hendriks H. M. J. , Reedijk J.
Published: September 2010

In a search for model compounds of copper‐containing proteins several Cu(II) and Cu(I) chloride complexes with 2‐isopropylimidazole, benzimidazole, 1‐benzylimidazole and 2‐phenylimidazole have been synthesized and characterized with the help of analytical data, IR, far‐IR, EPR and electronic spectra and magnetic susceptibility measurements. The Cu(I) complexes were produced either with anionic ligands or with the neutral ligands and chloride as counter ion. Some of these Cu(I) compounds are very stable, others are re‐oxidized in moist air and molecular formulae are given for these oxidation products. It appears that Cu(I) compounds are the more stabilised when bulky substituents are present in the ligands.
Chemistry of peroxyacyl nitrates II: Reactions in alcoholic solution; formation and subsequent conversion of peroxyacid
Authors: van Swieten A. P. , Louw R.
Published: September 2010

Peroxycapronyl nitrate 1 decomposes at equal rates in methanol and 2‐propanol, significantly faster than in cyclohexane. There appears to be no direct reaction between (aqueous) alcohol and 1, however. When (other) nucleophiles are absent, O‐NO2 homolysis is the rate‐determining step; RCO3* radicals abstract hydrogen from solvent to give peroxycarboxylic acid RCO3H (2). This largely survives reaction in 2‐propanol, but in methanol it is converted into methyl caproate. This process is found to be acid‐catalysed.

Peroxycaproic acid 2 also appears to react rapidly with NO2 ‐ whether in alcoholic or cyclohexane solution ‐ very probably via a free‐radical mechanism.

Rates and products of reaction of 1 in (aqueous) tert‐butanol closely resemble those in cyclohexane.
Studies on polypeptides XXX. Replacement of histidine‐12 by β‐(4‐pyridyl)‐L‐alanine in RNase S': (Preliminary communication)
Authors: Hoes C. , Hoogerhout P. , Bloemhoff W. , Kerling K. E. T.
Published: September 2010

[β‐(4‐pyridyl)‐L‐alanine12]RNase S‐peptide 1–14 was synthesized by the solid‐phase method. The peptide was found to bind strongly to RNase S‐protein; this binding was accompanied by specific changes in the UV spectrum of the pyridyl chromophore. The RNase S' analogue showed appreciable activity (28–34%) when acting on RNA; lower activities (0.4–4%) were observed using CpC and 2′,3′‐CMP as the substrate.
Metal catalysis in oxidation by peroxides. Part 5. On the mechanism of vanadium(V) catalysed oxidation by hydrogen peroxide
Authors: di Furia Fulvio , Modena Giorgio
Published: September 2010

The oxidation of p‐chlorophenyl methyl sulphide and of a series of phenyl substituted aryl methyl sulphides with hydrogen peroxide in the presence of catalytic amounts of bisacetylacetonato‐oxovanadium(IV) [VaO(acac)2] in ethanol, at 25°C, has been studied. The reaction affords the parent sulphoxide in quantitative yield. Oxidation rates are little affected by substitution in the phenyl ring of the sulphide. Comparison with vanadium catalysed oxidation of sulphides by tert‐butyl hydroperoxide shows that the Va(V)‐H2O2 system is much more effective than Va(V)‐ButO2H system. The initial rates of the reaction, which is first‐order in sulphide and in vanadium catalyst, show a rather complicated dependence on the initial concentration of the peroxide. Initial rates are found to increase with increasing [H2O2]0 at low peroxide initial concentration, then decrease at higher [H2O2]0; both the positive and the negative dependence show a fractionary kinetic order. Also on the ground of a kinetic investigation of the Va(V) catalysed autodecomposition of H2O2, which proceeds at measurable rate only at much higher Va(V) concentrations than those employed in the oxidation experiments, the involvement of two peroxyvanadium(V) species in the oxidation mechanism, corresponding to the equilibrium addition of one and two molecules of H2O2 to Va(V), respectively, is suggested. Whereas the mono‐adduct is believed to be a strong oxidant, the di‐adduct appears to behave, in our system, as a much weaker oxidizing agent. This is likely related to the fact that, in the conditions adopted, the di‐adduct may be largely ionized to its monoanionic form.
Photoisomérisation des quelques cyclohexadiènes et heptatriènes. Photocycloaddition des hexatriènes
Authors: Courtot Pierre , Rumin René , Salaün Jean‐Yves
Published: September 2010

Photolytic ring opening of cis and trans‐1,5‐diphenyl‐6‐méthylcyclohexa‐1,3‐dienes yields a unique primary triene with a geometry determined by the cyclodiene preferred conformation in the ground state.

Irradiation of 3 isomers of 1,5‐diphenylhepta‐1,3,5‐triene with a cis‐central double bond (Z, Z, E; E, Z, E and E, Z, Z) yields with a complete stereospecificity 3 bicyclo[3.1.0]hexenes (respectively endo‐Me‐endo‐Ph; endo‐Me‐exo‐Ph and exo‐Me‐exo‐Ph). Kinetic measurements have shown that these internal photocycloadditions are of the type [4πa + 2πa], which is forbidden by Woodward‐Hoffmann rules. In all of the three cases studied by us, orbital factors seem anyway to play a major role compared to steric constraints (an endo‐endo photoproduct is formed).

A kinetic study of the relative cis‐trans photoisomerization rates of carbon double bonds of the eight isomers of 1,5‐diphenylhepta‐1,3,5‐triene has been performed.
The oxidation of 7‐(p‐X‐phenyl)pteridin‐4‐ones (X = Me, H, Br, CN, NO2) with free and immobilized xanthine oxidase
Authors: Tramper J. , Nagel A. , van der Plas H.C. , Müller F.
Published: September 2010

Bovine milk xanthine oxidase was used as a catalyst for the oxidation of various 7‐(p‐X‐phenyl)pteridin‐4‐ones into 7‐(p‐X‐phenyl)lumazines. On a preparative scale the derivatives with X = Br, CN and NO2 were most conveniently oxidized with the free enzyme in a solution continuously fed with concentrated substrate. The lumazines obtained separated during the reaction and were easily isolated in good yield (> 90%) and high purity by filtration. The compounds with X = H and OMe, on the other hand, were more conveniently oxidized with the immobilized enzyme, i.e. xanthine oxidase adsorbed to 1‐octyl‐substituted Sepharose 4B. Immobilized xanthine oxidase was used either as a suspension in a stirred batch reactor which was continuously fed with concentrated substrate, or packed in a column through which substrate solution was recirculated. After completion of the reaction the filtrate of the suspension, or the concentrated recirculation solution, respectively, were acidified and the product was collected in good yield (> 90%) and high purity by filtration. The rate of oxidation was found to be influenced by the substituent X. The more electron attracting X, by either resonance or induction, the lower the reaction rate. Accordingly, a negative reaction constant ρ of ∼ −0.5 was calculated from the data for the free and immobilized enzyme. The enzyme‐substrate complex formation, as reflected in the Michaelis constant Km, is largely determined by the hydrophobicity of the phenyl group.
Synthesis and structures of 2,4,5‐trialkyl‐2,3,4,5‐tetrahydropyrimidines and 2,5,6,8,9‐pentalkyl‐1,3,7‐triazabicyclo[3.3.1]non‐3‐enes
Authors: Oude‐Alink B. A. M.
Published: September 2010

The reaction products resulting from deammoniation of 2,4,6‐trialkylhexahydro‐1,3,5‐triazine (1a‐c) derived from n‐alkyl aldehydes (propanal, butanal and pentanal) have been identified as 2,4,5‐trialkyl‐2,3,5‐tetrahydropyrimidines and 2,5,6,8,9‐pentalkyl‐1,3,7‐triazabicyclo[3.3.1]non‐3‐enes.
Convenient preparations of ω‐substituted picoline N‐oxides utilising triphenylpyridinium intermediates
Authors: Katritzky Alan R. , El‐Mowafy Azzahra M. , Patel Ranjan C.
Published: September 2010

3‐ and 4‐Picolylamines are converted by 2,4,6‐triphenylpyrylium cation into pyridinium salts which can be N‐oxidised in high yield. The resultant N‐oxopyridinium salts react with pyridine and with sodium thiophenoxide to give ω‐substituted 3‐ and 4‐picoline N‐oxides in high overall yields.
3‐Methoxypropen‐2‐yl formate, a selective reagent for the formylation of alcohols or phenols
Authors: Scheeren J. W. , Bats H.
Published: September 2010

An improved synthesis is given for the selectively amino formylating reagent, 3‐methoxypropen‐2‐yl formate. The compound can also be used for selective formylation of either alcohols or phenols by using an acid or tertiary amine as a catalyst.
MO‐SCF calculations on protonated butatriene and 1,2,3‐pentatriene
Authors: Mirejovsky D. , Drenth W. , van Duijneveldt F. B.
Published: September 2010

Energies are calculated for the cations obtained by protonation of butatriene and 1,2,3‐pentatriene at various positions. The relative stabilities of the various ions are discussed. The ion of lowest energy is an allylic cation obtained by rotation around a CC bond after or concomitant with protonation. Experimentally, instead of this ion the next higher in energy is formed. The latter is a propargylic ion, formed by proton attack at the terminal carbon atom. Apparently, rotation is not appreciable in the transition state of the experimental protonation.
A method for the quantitative determination of juvenile hormones in insects
Authors: Huibregtse‐Minderhoud L. , van der Kerk‐Van Hoof A. C. , Wijkens P. , Biessels H. W. A. , Salemink C. A.
Published: September 2010

A method to determine the content of the juvenile hormones in insects as low as 0.2 nanogram per sample was developed. The juvenile hormones were transformed in their 10‐hepta‐' fluorobutyrate‐11‐methoxy‐derivatives and simultaneously determined by capillary gas chromatography with electron capture detection.
Photoreactions of o‐vinyltriphenylethylenes II. Photochemistry of 1,1‐diphenyl‐2‐(o‐vinylphenyl)‐ and 1,1‐diphenyl‐2‐(o‐propenylphenyl)ethylene
Authors: Sindler‐Kulyk M. , Laarhoven W. H.
Published: September 2010

Irradiation of 1,1‐diphenyl‐2‐(o‐vinylphenyl)ethylene (3) leads stereoselectively to endo‐4,5‐diphenylbenzobicyclo[3.1.0]hex‐2‐ene (6). The analogous reaction of the homologous (o‐propenylphenyl)ethylene derivative (4) seems to be less stereoselective, as products 10 and 11 could be isolated. In both cases a photodehydrocyclisation product (7 and 12, respectively) is also found. Possible mechanisms for the photocyclisation reactions are discussed, and the photochemical behaviour of 3 and 4 is compared with that of other o‐vinylstilbenes, previously investigated.
The photosensitized oxidation of the 19‐norsteroids: 17α‐19‐norpregn‐5‐en‐20‐yne‐3β,17‐diol, 3β‐chloro‐17α‐19‐norpregn‐5‐en‐20‐yn‐17‐ol and 17α‐19‐norpregn‐5‐en‐20‐yn‐17‐ol
Authors: Peters J. A. M. , van Vliet N. P. , Zeelen F. J.
Published: September 2010

Photosensitized oxygenation of 19‐norsteroids with a 5–6 double bond proceeds with high stereoselectivity to give, after reduction of the initially formed hydroperoxides, 5α‐hydroxy 6‐enes as the major products. Higher amounts of 6β‐hydroxy 4‐enes, the minor products, are formed than in the case of cholesterol. These results are in agreement with the “ene” mechanism proposed by Schenck and Nickon and not with the peroxirane mechanism proposed by Dewar and Thiel.
Synthesis, characterisation and complex formation of N,N,N′,N′‐tetrakis‐(2‐benzimidazolylmethyl)‐1,2‐ethanediamine, a new hexadentate ligand
Authors: Hendriks H. M. J. , ten Bokkel Huinink W. O. , Reedijk J.
Published: September 2010

The synthesis and complex formation of a new hexadentate, nitrogen‐donor ligand are described. The ligand N,N,N′,N′‐tetrakis(2‐benzimidazolylmethyl)‐1,2‐ethanediamine (EDTB) is prepared by condensation of 1,2‐benzenediamine and ethylenediaminetetraacetic acid. This chelate ligand appears to be able to solvate first‐row transition‐metal ions in an octahedral manner, resulting in species M(EDTB) (anion)2 and M2(EDTB) (anion)4. The products have been analysed and characterised by spectroscopic and magnetic techniques (EPR, NMR, ligand‐field and IR).

During recent years much interest has arosen in the bioinorganic chemistry of first‐row transition‐metal ions, in particular with respect to the relationships between the activity and structural properties of metalloproteins, such as hemocyanin, tyrosinase, laccase, cytochrome‐c‐oxidase, superoxide dismutase and carbonic anhydrase.1–3

Nitrogen‐donor ligands such as imidazoles of polypeptidyl histidines have been shown to play an important rǒle in the coordination of the metal ions in such proteins. 4,5 Furthermore, the stereochemistry imposed by the rigid structure of the protein seems to be responsible for some of the characteristic properties and the activity of metalloproteins.6
Studies on polypeptides XXXI. An approach to the chemical semisynthesis of ribonuclease A analogues. Part I: The preparation of N‐acetimidoyl‐S‐protein
Authors: Hoogerhout P. , Bloemhoff W. , Kerling K. E. T.
Published: September 2010

The limited proteolysis of acetimidated ribonuclease A by subtilisin has been investigated. Evidence of the cleavage being restricted to the Ala20–Ser21 bond is presented. N8ε‐acetimidyl‐S‐protein, an intermediate for the chemical semisynthesis of ribonuclease A analogues, can be obtained in an over‐all yield of 46% starting from ribonuclease A.

A new method to follow the subtilisin‐catalyzed cleavage reaction of ribonuclease A and derivatives, applying reverse‐phase high‐performance liquid chromatography, is reported.
X‐ray structure determination of the phosphite triester of methyl β‐D‐ribopyranoside; CNDO‐2 calculation
Authors: Bellaart A. C. , van Aken D. , Buck H. M. , Stam C. H. , van Herk A.
Published: September 2010

The phosphite triester (6), the O,O,O‐thiophosphate triester (7), and the phosphate triester (8) of methyl β‐d‐ribopyranoside were prepared. Crystal structures of 6 and 7 were determined by X‐ray diffraction. Quantum‐chemical calculations were performed on 6. They clearly demonstrate that the positive charge on phosphorus is relatively high. This high charge is a result of the strain in the ester moiety of 6.
On the formation of allenes in the steroid series IV. Synthesis and structure of several 3‐methoxy‐19‐nor‐1,3,5(10)‐17(20), 20‐pregnapentaenes, substituted at C(21)
Authors: van Dijck L.A. , Lankwerden B.J. , Vermeer J.C.G.M.
Published: September 2010

Pairs of steroid 17(20),20‐allenes, epimeric at C(21), have been obtained by LiAlH4(D4)/AlCl3 reduction of 17α/β‐hydroxy‐17β/α‐alkynyl steroids, confirmed by means of optical rotation differences and NMR spectroscopy. In all cases the reduction proved to be fully stereospecific, confirming the cis‐SN2′ mechanism, postulated in part II1.

In addition, the NMR spectra of 17‐(trans‐1‐alkenyl) 17‐hydroxy compounds, obtained as by‐products or especially prepared, have been analysed. Finally the structure of a dideuterioallene, tentatively described as a 16β,21α‐dideuterio‐17(20),20‐allene in part III2, has been proved by full analysis of the 300 MHz spectra of allenic model compounds.
Reactions d'addition nucléophile sur les cétones. Rǒle des facteurs stériques à longue distance dans les réactions d'addition de l'ion sulfite et de l'hydroxylamine
Authors: Boyer B. , Lamaty G.
Published: September 2010

Rate constants have been measured for the addition of sulphite ion and hydroxylamine on a series of sterically hindered cyclohexanones as well as for the decomposition of the bisulphite adducts. The observed differences in reactivity mau be regarded as resulting from the intervention of the “steric compression effect” due to the axial substituents. Calculated δΔG≠ values confirm the existence of such an effect and the results are consistent with the intermediate formation of a “reactant‐like” transition state in these reactions.
A combined study of vicinal and geminal carbon‐proton spin‐spin coupling constants as a tool in conformational analysis. The conformation of 2,6‐dichloro‐1,4‐oxathianes
Authors: Spoormaker Tom , de Bie Marius J. A.
Published: September 2010

13C FT single resonance spectra are obtained for two isomers of 2,6‐dichloro‐1,4‐oxathiane; one of the isomers is a racemic mixture. From a combined study of the various long‐range carbon‐proton coupling constants the conformations of both isomers could be determined. Each isomer exists in two conformers which are in a rapid interconversion equilibrium. Contrary to predictions based on the “anomeric‐effect”, cis‐2,6‐dichloro‐1,4‐oxathiane in the liquid phase is predominantly in the cis‐di‐equatorial chair form.
Thiophilic additions of functionalized carbanions to sulfines
Authors: Loontjes J. A. , van der Leij M. , Zwanenburg B.
Published: September 2010

The reaction of three types of sulfines with functionalized carbanions is described. Di‐p‐tolylsulfine 1 reacts with excess of MeSOCH2Na at the sulfine sulfur atom (thiophilic addition) to give Tol2CHS(O)CH2SOMe (Tol = p‐MeC6H4). Similarly, acetonitrile with excess of sodium amide adds thiophilically. N,N‐Diethyl χ‐lithio‐n‐butyramide and dilithio‐n‐butyric acid also form thiophilic addition products. Methyl p‐tolyl sulfone in the presence of BuLi and excess of t‐BuOK affords the adduct Tol2CHS(O)CH2SO2Tol, whereas lithiomethyl p‐tolyl sulfone furnishes alkenesulfone Tol2CCHSO2Tol. It is presumed that the primary adduct rearranges via a thiocarbonyl ylide and an episulfide. From α,α‐dilithiobenzyl cyanide Tol2CC(Ph)CN is obtained by a similar rearrangement. α‐Lithioisopropyl p‐tolyl sulfone with sulfine 1 gives the olefin Tol2CCMe2 which arises from a Ramberg‐Bäcklund type rearrangement of the primary thiophilic adduct. Similarly, p‐tolyl(phenylthio)sulfine 2 and p‐tolyl(phenylsulfonyl) sulfine 3 give thiophilic addition products with some of the carbon nucleophiles mentioned above. The mechanism of the thiophilic reaction is discussed.
Synthesis, crystal structure and properties of the spin singlet six‐coordinated Ni(II) compound Ni(Et2dtc)2(AsI3)2
Authors: Willemse J. , Cras J. A. , Bosman W. P. , Steggerda J. J.
Published: September 2010

The reaction of Ni(R2dtc)2 (R  Et, Bu) with AsI3 yields a product which could be characterised as Ni(R2dtc)2(AsI3)2. The crystal structure of the compound with R  Et [space group P21/C, Z = 2, a = 8.428(1), b = 19.692(2), c = 9.194(1) Å, β = 102.24(2)°] revealed that the nickel atom is coordinated by four dithiocarbamato sulfur atoms and two arsenic atoms in pseudo‐octahedral geometry. Magnetic susceptibility measurements show these six‐coordinated Ni(II) compounds to have a spin singlet ground state.
Thin‐film dye sensitization and impurity effects on TiO2 and SrTiO3 electrodes for the photoelectrolysis of water
Authors: Mackor A. , Schoonman J.
Published: September 2010

Single crystals of TiO2 and SrTiO3 are sensitized by thin films of a ruthenium surfactant dye, which is able to sustain catalytic oxidation of water upon irradiation with visible light. Calculated turnover numbers exceed 2000. Doping of the crystals with niobium does not improve the suitability of these semiconductors as photoanodes, contrary to results obtained with polycrystalline Nb‐doped TiO2.
The amination of 3‐bromo‐2‐ethoxy‐1,5‐naphthyridine. A reinvestigation
Authors: van den Haak H. J. W. , van der Plas H. C.
Published: September 2010

The reaction of 3‐bromo‐2‐ethoxy‐1,5‐naphthyridine with KNH2/NH3 was reinvestigated. The procedure, described in the literature for the preparation of the title compound does not lead to this compound but to the isomeric 3‐bromo‐1‐ethyl‐1,5‐naphthyridin‐2(1H)‐one. Reaction of this compound with KNH2/NH3 yields 3‐ and 4‐amino‐1‐ethyl‐1,5‐naphthyridin‐2(1H)‐one, the latter being the main product. The title compound was prepared on reacting 2,3‐dibromo‐1,5‐naphthyridine with sodium ethoxide. A mixture of 3‐ and 4‐amino‐2‐ethoxy‐1,5‐naphthyridine was obtained on amination of 3‐bromo‐2‐ethoxy‐1,5‐naphthyridine. In both cases the intermediacy of the respective 3,4‐didehydro compounds was proposed.
Acidity constants of some aromatic astatine compounds
Authors: Visser Gerard W. M. , Diemer Eduard L. , Kaspersen Frans M.
Published: September 2010

The acidity constants of [211At]‐astatobenzoic acids, ‐phenols, ‐anilines and 5‐astatouracil have been determined by measurement of the distribution coefficients between water and an organic phase as a function of the pH. On the basis of the acidity constants of the phenols and anilines the σm and σp constants for astatine were calculated as +0.25 and +0.18, respectively. From these values it can be concluded that the field (F) effect of astatine is weaker than that of iodine, whereas the resonance (R) effect is about the same.
Synthesis of the 2‐ethyl‐3‐methylsuccinic acidsviaa stereospecific malonic ester alkylation
Authors: van Leeuwen F. F. , Noordam A. , Maat L. , Beyerman H. C.
Published: September 2010

Reaction of (−)‐(S)‐methyl 2‐bromopropionate (4) (obtained from l‐alanine) with dibenzyl ethylmalonate gave stereospecifically in four steps ( + )‐(2R,3S)‐2‐ethyl‐3‐methylsuccinic acid (8a) and its diastereoisomer (8b). The malonic ester alkylation proceeded with Walden inversion. The chiroptical properties of the acids and the intermediates are in conformity with the known absolute configurations.
Studies on polypeptides XXXII: Solid‐phase synthesis of RNase S‐peptide 1‐14 analogues; replacement of histidine‐12 by β‐(2‐pyridyl)‐L‐alanine and β‐(4‐pyridyl)‐L‐alanine
Authors: Hoes C. , Raap J. , Bloemhoff W. , Kerling K. E. T.
Published: September 2010

The synthesis of two analogues of the N‐terminal tetradecapeptide of ribonuclease A (RNase S‐peptide 1‐14), in which the active site histidine‐12 residue is replaced by β‐(2‐pyridyl)‐L‐alanine and β‐(4‐pyridyl)‐L‐alanine, has been accomplished by the solid‐phase method.

The enantiomers of β‐(2‐pyridyl)alanine were obtained by chymotryptic hydrolysis of its racemic Nα‐acetyl ethyl ester. The Boc derivative of both L‐amino acids has been synthesized.
The photooxidation of mono‐ and dimethylnaphthalenes by singlet oxygen
Authors: van den Heuvel C. J. M. , Steinberg H. , de Boer Th. J.
Published: September 2010

The reactions of singlet oxygen with all possible isomers of mono‐ and dimethylnaphthalenes as well as with 1,4,6,7‐tetramethylnaphthalene have been studied. Apart from 2‐methylnaphthalene, which does not react under our reaction conditions, attack on 1,4‐ and in some cases also on 5,8‐positions results in the formation of endoperoxides (epidioxides). In the case of 1,4‐dihydro‐2,3‐dimethyl‐1,4‐epidioxynaphthalene there is a subsequent reaction step with singlet oxygen which introduces an allylic hydroperoxy function.

The structures of the endoperoxides were established by means of NMR. A simple volumetric method was employed to measure the relative reaction rates. Rate constants (15°C) for the mono‐ and dimethylnaphthalenes vary over a range of 103 M−1s−1. The differences in reactivity can be logically explained by the activating effect of the methyl substituents.

On heating, the endoperoxides decompose quantitatively back to starting materials.
Sigma‐assistance, an unrecognized factor in organic reactivity
Authors: Verhoeven J. W.
Published: September 2010

A simple perturbational frontier molecular orbital description with inclusion of sigma electrons is presented for bifunctional intramolecular reactivity. This description readily accounts for the preferred formation of odd membered rings in (di) radical cyclization and of even membered transition states in intramolecular hydrogen or hydride migration.
Coordination and activation of the NS bond in sulfurdiimines RNSNR and sulfinylanilines RNSO by metal atoms
Authors: Vrieze Kees , van Koten Gerard
Published: September 2010

A survey is given of the coordination chemistry of sulfurdiimines RNSNR and sulfinylanilines RNSO towards metal atoms. It is shown that these pseudoallene ligands which are isostructural and isoelectronic with SO2 may coordinate via N, S or via the π‐NS double bond. Nitrogen coordination is favoured by metals in the higher oxidation states e.g. PtII, PdII, but may also occur for Rh1 and If and even for zerovalent metals such as Cr°, Mo° and W°. Sulfur coordination probably occurs for Cr°, Mo° and W°, but has been observed for Rh1 and Ir1. Finally, metal‐π‐N=S bonding is clearly favoured by electron‐rich metal atoms like Ni°, Pd°, Pt°, Rh1 and Ir1. In the case of metal‐ π2‐N=S coordination of the RNSNR ligands further reactions may occur which lead to NS bond rupture. Such bond rupture may result in a large number of reactions varying from simple insertion of a metal atom into an N‐S bond to the formation of RNS, S and NR fragments which are captured in metal cluster complexes. Other ways of converting the RNSNR ligand involve the reactions with LiR′, R′MgX and trialkylaluminium compounds. The anionic RNS(R′)NR ligand so formed may behave as a bridging ligand but, more interestingly, as a pseudoallylic chelate group. It is shown that RNS(R′)NR− bonded as a chelate to transition metal atoms decomposes stereospecifically into azo compounds and SR− fragments.
Oxidation of (‐)‐2‐bromo‐3‐hydroxy‐N‐methyl‐6‐oxomorphinan with Fremy's salt. An unprecedented 2,4‐shift of the bromo substituent. (Chemistry of opium alkaloids, Part XIII)
Authors: Olieman C. , Maat L. , Beyerman H. C.
Published: September 2010

(‐)‐3‐Hydroxy‐N‐methyl‐6‐oxomorphinan (6a) and its (‐)‐2‐bromo derivative (6b) were converted into (‐)‐2,3‐dihydroxy‐N‐methyl‐6‐oxomorphinan (8a) and its (‐)‐4‐bromo derivative (8b), respectively, by oxidation with Fremy's salt to the ortho‐quinones, followed by reduction. Methylation of 8a and 8b gave the corresponding methyl ethers 9a and 9b. Catalytic hydrogenolysis of 8b and 9b gave 8a and 9a, respectively. The structure of (‐)‐2,3‐dimethoxy‐N‐methyl‐6‐oxomorphinan (9a) was confirmed by total synthesis, and that of (‐)‐4‐bromo‐2,3‐dimethoxy‐N‐methyl‐6‐oxomorphinan (9b) by single‐crystal X‐ray analysis.

The model compound 2‐bromo‐4,5‐dimethylphenol (15) gave, analogously, 3‐bromo‐4,5‐dimethyl‐pyrocatechol (16).
Sulfenylation of dithio ester anions
Authors: Sukhai R. S. , de Jong R. , Meijer J. , Brandsma L.
Published: September 2010

The anions derived from dithio esters 1 react with alkyl alkanethiosulfonates in 1,2‐dimethoxyethane to give the S‐sulfenylated products 3. Nucleophilic reagents like potassium tert‐butoxide, dithio ester anions or ‐ in some cases ‐ even (liquid) ammonia catalyse the rearrangement of 3 into the C‐sulfenylated compounds 4. The latter compounds can be isolated directly, if the dithio ester anions 2 are allowed to react with thiosulfonates in liquid ammonia or with thiocyanates in dimethoxyethane or liquid ammonia.
Geminal carbon‐proton spin‐spin coupling constants in ethyl, isopropyl and tert‐butyl compounds
Authors: Spoormaker Tom , de Bie Marius J. A.
Published: September 2010

The geminal 13C1H coupling constants in ethyl, isopropyl and tert‐butyl compounds having elements of the first row of the Periodic Table and halogens as substituents are determined by single resonance 13C FT NMR spectroscopy. In addition, the values of directly bonded 13C13C coupling constants are given. The substituent electronegativity dependence of the geminal 13C1H coupling constant is discussed. It is concluded that the influence exerted by a β‐methyl substituent on the geminal 13C1H coupling constant of 13Cα‐Cβ‐1H fragments is not constant and hence no simple additivity relation can be established for this coupling constant.
The electrochemical Wittig‐Horner reaction; evidence of a stepwise cleavage of a four‐membered ring Wittig intermediate
Authors: van Tilborg W. J. M. , Smit C. J.
Published: September 2010

Electro‐reduction of diethyl(trichloromethyl)phosphonate in the presence of aldehydes or ketones replaces the oxygen atom of the carbonyl group by a dichloromethylene group. The yield of 1,1‐dichloroethene product decreases substantially if the carbonyl compound carries strongly acidic hydrogen. In several cases the conversion of the four‐membered ringWittigintermediate into its corresponding carbanion by heterolytic PC bond cleavage is observed. The intermediate carbanion is sufficiently stable to be intercepted by proton abstraction. These observations suggest that, at least with our substrates, the decomposition of theWittigfour‐membered ring intermediate occurs along a two‐step path way.
Texture of zeolites and zeolite‐containing solids
Authors: Aneke L. E. , de Jong W. A. , van den Berg P. J.
Published: September 2010

Texture studies, in which specific surface area and total pore volume were determined by low temperature nitrogen adsorption, were carried out on a number of porous solids, ranging from cation‐exchanged Y‐zeolites, impregnated with β‐AlF3 and copper, to steamed silica‐alumina. The zeolites were impregnated with β‐AlF3 and Cu in order to improve their Toluene disproportionation performance.

After comments on the applicability of the conventional approaches to zeolites and zeolite‐containing solids, a new method is proposed for calculating of the surface area of this class of compounds. This method makes use of the micropore volume, determined by De Boer's t‐method, and the surface area and volume of a zeolite cage, calculated from X‐ray data.
The photo‐oxidation of hexamethylbenzene and pentamethylbenzene by singlet oxygen
Authors: van den Heuvel C. J. M. , Hofland A. , Steinberg H. , de Boer Th. J.
Published: September 2010

In a two step reaction, hexamethylbenzene consumes two molecules of singlet oxygen to form epidioxy hydroperoxide 3. The first step involves a [4 + 2]‐cycloaddition, which is followed by an ene‐reaction. The structure of the intermediary endoperoxide 2 has been established spectroscopically. Pentamethylbenzene reacts in the same way with singlet oxygen, albeit much more slowly. Two epidioxy hydroperoxides are formed in this case.
Triplet‐sensitized interconversion and photooxygenation of Vitamin D and trans‐Vitamin D
Authors: Gielen J. W. J. , Koolstra R. B. , Jacobs H. J. C. , Havinga E.
Published: September 2010

Triplet‐sensitized irradiation of either Vitamin D or transVitamin D establishes a photo‐equilibrium between the two isomers, the position of which varies with the triplet energy of the sensitizer. In the presence of oxygen, selective photooxygenation of trans‐Vitamin D takes place. The applicability of sensitization for the preparation of cis‐ and trans‐Vitamin D and derivatives thereof is shown.
Nickel(II) complexes of deprotonated thiourea; Crystal structure of Ni[(C6H5)NC(S)N{(C2H4)2O}]2
Authors: Janakiram‐Sayala Chhaya , Bosman W. P. , Willemse J. , Cras J. A.
Published: September 2010

Nickel(II) complexes with deprotonated trisubstituted thiourea were prepared. The crystal structure of Ni[PhNC(S)N{(C2H4)2O}]2 showed that the nickel atom is centrosymmetrically square planar coordinated through the N and S of the thioureido ligands. The diamagnetic compound crystallizes in the monoclinic space group C2/c [a = 24.146(3), b = 10.480(2), c = 9.473(3) Å, β = 106.38(1)°] and contains four formula units per unit cell.
10‐Mono‐, 11‐mono‐, 12‐mono and 11,12‐dideuteroretinal
Authors: Broek A. D. , Lugtenburg J.
Published: September 2010

The 11‐mono and 12‐mono‐ and 11,12‐dideuteroretina1 (in the all‐trans, 9‐cis, 11‐cis and 13‐cis form) with > 98% chemical purity and > 95% mono‐ and dideuterium incorporation were prepared using the same scheme for all three compounds. The all‐trans, 9‐cis and 13‐cis‐10‐monodeuteroretinal isomers were prepared with good chemical purity (> 99%) and 82% monodeuterium incorporation via a different reaction scheme.
Enzymatic synthesis of a peptide bond between a tryptic fragment of horse heart cytochrome c and a synthetic model peptide
Authors: Westerhuis L. W. , Tesser G. I. , Nivard R. J. F.
Published: September 2010

As a model study for the usefulness of the synthetic action of a proteinase in the semisynthesis of large polypeptides, a heme peptide, comprising the residues 1‐38 of horse heart cytochrome‐c and bearing protective functions on the ϵ‐amino groups, was incubated with trypsin in the presence of H‐Orn(Msc)‐Trp‐NHCH3 in a mixture of water and organic solvents. We found that the proteolytic enzyme catalysed the formation of a peptide bond between the fragment and the dipeptide derivative.
Tautomeric pyridines. Part XXIV. Tautomeric equilibria for 3‐ethoxycarbonyl‐, 3‐ethoxycarbonyl‐6,7‐methylenedioxy‐, and 3‐cyano‐4‐quinolone
Authors: Katritzky Alan R. , Ellison Joan , Frank Judit , Mészáros Zoltán
Published: September 2010

Ultraviolet spectra and pKa values for the title compounds and their O‐ and N‐ethyl derivatives show that in each case the quinolone form is favoured in aqueous solution. The results are compared qualitatively with those for 4‐quinolone and for findings in the gas phase.
An improved synthesis of 1,2,3‐butatrienyl ethers
Authors: Visser R. G. , Bos H. J. T. , Brandsma L.
Published: September 2010

A modified synthetic route to 1,2,3‐butatrienyl ethers 3 is presented. It involves hydroxyalkylation of 2‐propynyl ethers with an aldehyde or a ketone, followed by trimethylsilylation of the hydroxy ether 1 and 1,4‐elimination of Me3SiOH from 2 with ethyllithium.
Application of levulinic acid ester as a protective group in the synthesis of oligosaccharides
Authors: Koeners H. J. , Verhoeven J. , van Boom J. H.
Published: September 2010

The fast, selective and mild removal of levulinoyl groups with hydrazine from galactose, which also carries hydroxyl functions protected with acetyl groups, enabled us, under Koenigs‐Knorr conditions, to synthesize tri‐ and tetrasaccharides containing β‐linked galactose and glucose units. Selective acylation of the primary alcoholic group of the partially protected galactose derivative 13b with levulinic acid was achieved in good yield. The preparation of tetrasaccharide 18b, having a free hydroxyl function, was effected by condensing dimer 16b with the bromo derivative 17, followed by the removal of the levulioyl group with hydrazine.
An additivity relation for carbon‐13 chemical shifts in substituted allenes
Authors: Janssen R. H. A. M. , Ch. Lousberg R. J. J. , de Bie M. J. A.
Published: September 2010

An empirical method for the calculation of the carbon chemical shifts of allene carbons is developed. The method is successful in predicting the chemical shifts in a wide variety of substituted allenes.

The effect of the electronegativity of substituents, with respect to the chemical shift contributions, is discussed.

Experimental chemical shift increment values show a linear correlation with both the calculated diamagnetic shielding effects and the Pauling electronegativities for first row elements of the periodic system directly attached to the allene.
R3Cu2M species: Convenient cuprates for the conversion of 1‐alkynes into 1‐alkenes
Authors: Westmijze H. , Kleijn H. , Meijer J. , Vermeer P.
Published: September 2010

The paper describes reactions of 1‐alkynes, R1‐C≡C‐H, with new cuprate species of the type R3Cu2M [M = Mg(Cl, Br)]. Under suitably chosen conditions a smooth transfer of R (Me or Et) from the cuprates to the 1‐alkynes (R1 = Ph or n‐C6H13) could be realized. The resulting stereospecifically generated adducts [(RR1CCH)xCu2R3‐x]Mg (Cl or Br) were stable under the conditions of the reactions, provided that a sufficient amount of lithium bromide was present. In the absence of lithium bromide substantial decomposition of the adducts into RR1CCH‐CHCRR1 took place. During the reaction of PhC≡CH with Me3Cu2Li the addition reaction was accompanied by deprotonation, which could be proved by using PhC≡CD as starting alkyne. Deprotonation in PhC≡CH as side‐reaction also occurred with Me3Cu2MgBr. The latter complex was prepared from MeMgBr and CuBr.

The number of R groups which are transferrable from R3Cu2M to R1‐C≡CH with an acceptable rate appeared to depend on the nature of R, viz. One R group in the case of Me3Cu2M and all three R groups in the case of Et3Cu2M.
Conformational studies on helicenes VI. A comparison between experimental and calculated conformations
Authors: Somers J. B. M. , Borkent J. H. , Laarhoven W. H.
Published: September 2010

The force‐field method of Warshel has been used for the calculation of the conformations of hexahelicene, two methyl substituted hexahelicenes and heptahelicene. The calculated models have been compared with the known X‐ray structure and the generally small differences have been discussed.

The method has also been used for the calculation of the structure of 5,6‐dihydrohexahelicene. The dihedral angles in the aliphatic moiety of the model agree reasonably well with those calculated from NMR data.
4,4‐(Ethylenedithio)pentanoyl: A masked levulinoyl protective group in the synthesis of oligosaccharides
Authors: Koeners H. J. , Verdegaal C. H. M. , van Boom J. H.
Published: September 2010

In this study we demonstrate that the 4,4‐(ethylenedithio)pentanoyl group can be used for the protection of hydroxyl functions of glucose and galactose. Selective acylation of the primary alcoholic function of the galactose derivative 1a was accomplished using 4,4‐(ethylenedithio)pentanoyl chloride. Furthermore, we show that the 4,4‐(ethylenedithio)pentanoyl group can easily be converted into the levulioyl group and that the dithio‐acetal function is stable under the conditions required for the formation of interglycosidic linkages. Finally, a combined use of the levulinoyl and the 4,4‐(ethylenedithio)pentanoyl group enabled us to synthesize a branched tetrasaccharide containing glucose and galactose moieties.
Photochemistry of dienones. Part IX. Photochemistry of (E)‐ and (Z)‐α‐ionone
Authors: Visser Cornelis P. , Cerfontain Hans
Published: September 2010

The photochemical reactions of (E)‐α‐ionone (1) and its photoproducts have been re‐examined. Upon irradiation with λ 254 and 313 nm a sequence of photo‐reactions takes place: initially (Z)‐α‐ionone (2) is formed and subsequently (E)‐ and (Z)‐retro‐α‐ionone (4a and b), which eventually undergo a 1,3‐ and 1,5‐acyl shift to give 3‐acetyl‐2,4,4‐trimethyl‐3‐ (5) and 6‐acetyl‐1,3,3‐trimethyl‐2‐vinylcyclohexene (6), respectively. Evidence is presented for the intermediacy of the photo‐enol 3a in the photoconversion of the α‐ionone to retro‐α‐ionone. The multiplicities of the reacting excited states for the (E) → (Z)‐α‐ionone and the α‐ionone → retro‐α‐ionone conversions (using triplet photosensitization) and for the 1,5‐acyl shift of retro‐α‐ionone (using CIDNP) have been shown to be triplet, singlet, and singlet, respectively. Upon irradiation of 1 with λ 366 nm, instead of the shorter wavelengths, the reaction stops at the (E)‐ and (Z)‐retro‐α‐ionone stage. Variation in the solvent did not alter the course of the photoconversion.
Studies on polypeptides XXXVI. Chemical semisynthesis of a ribonuclease A analogue ([13‐isoleucine, 20‐homoserine] ‐ ribonuclease A)
Authors: Hoogerbout P. , Kerling K. E. T.
Published: September 2010

The peptide bond formation between synthetic [Ile13, Hse20]‐S‐peptide lactone and S‐protein leads to the formation of [Ile13, Hse20]‐RNase A. Coupling yields up to 7 % were obtained.
Base‐catalysed isomerization of 2‐propynylamines. Synthesis of (dialkylamino)allenes
Authors: Verkruijsse H. D. , Bos H. J. T. , de Noten L. J. , Brandsma L.
Published: September 2010

A number of (dialkylamino)allenes 2 have been obtained in excellent yields and in a reasonable state of purity by isomerization of dialkyl‐2‐propynylamines 1 with potassium tert‐butoxide in tetrahydrofuran or with the complex t‐BuOK.t‐BuOH in hexamethylphosphoric triamide. Treatment of the 2‐propynylamines with t‐BuOK in dimethyl sulfoxide leads to equilibrium mixtures of the allenic amines 2 and dialkyl‐1‐alkynylamines 3.
The bromination and iodination of N1‐substituted uracils
Authors: Bakker Cees N. M. , Kaspersen Frans M.
Published: September 2010

Reaction of N1‐substituted uracils with bromine in water at pH 7 leads to 5‐bromo‐6–hydroxy‐5,6‐dihydrouracils. For different N1‐substituents these products were isolated and the relatively stable derivatives were characterized by 1H NMR and mass spectroscopy. On electrophilic iodination with [131I]iodide and chloramine‐T in water no indications were obtained for the formation of such dihydrouracils except for uridine and deoxyuridine. However, on reaction of N1‐substituted uracils with N1‐iodosuccinimide in CHCl3 containing ethanol or in ethanol, 5‐iodo‐6‐ethoxy‐5,6‐dihydrouracils could be isolated as reaction products.
1,3‐Dipolar cycloadditions to alkyldicyanamides
Authors: Benders P. H. , Reinhoudt D. N. , van den Ham D. M. W.
Published: September 2010

The 1,3‐dipoles 2,4,6‐trimethylbenzonitrile oxide and benzyl azide react with alkyldicyanamides (1) to give the 3,5‐disubstituted 1,2,4‐oxadiazoles 2 and the 1,5‐disubstituted tetrazole 4, respectively, by (3 + 2)‐cycloaddition. The structure of 4 has been determined by a single crystal X‐ray analysis.
Base‐induced isomerization of 1,4‐dialkoxy‐2‐alkynes
Authors: van Rijn P. E. , Everhardus R. H. , van der Ven J. , Brandsma L.
Published: September 2010

1,4‐Dialkoxy‐2‐alkynes of structural types ROCH(R1)CCCH2 OR (R and R1 = alkyl) and ROC(R1)(R2)CCCH2OR (R = alkyl, R1 and R2 = alkyl or R1R2C(CH2)5) are converted into the allenic isomers under the influence of potassium tert‐butoxide in dimethyl sulfoxide. 1,4‐Dialkoxy‐2‐butynes RO‐CH2CCCH2OR under these conditions yield conjugated dienes of the type ROCHCHCHCHOR; the corresponding allenes, ROCHCCHCH2OR, can be prepared by using potassium tert‐butoxide in tetrahydrofuran or liquid ammonia.
Intérêt des spectres de RMN de 13C dans la série de la triazine‐,2,4
Authors: Daunis J. , Djouai‐Hifdi L. , Follet M.
Published: September 2010

L'étude d'environ 60 spectres de RMN de 13C de dérivés de la triazine montre qu'il est possible de déterminer leur structure isomère ou tautomère qui est liée à la nature et à la position des substitutions.
Synthesis and properties of 1,1′‐methylene‐2,2′‐dipyrrolyl ketone
Authors: de Groot J. A. , Koek J. H. , Lugtenburg J.
Published: September 2010

1,1′‐methylene‐2,2′‐dipyrrolyl ketone can be conveniently prepared in high yield, starting from pyrrole, in three steps. It shows extreme properties that are not observed in comparable rigid ketone systems. These chemical and physical properties can be explained assuming mesomeric forms with charge separation resulting from the electron rich pyrrole rings and the rigidity of the system. The fluorescence quantum yield is 0.07 and the fluorescence lifetime is 27 ns.
The electrosynthesis of carboxylic acids from carbon dioxide and butadiene
Authors: van Tilborg W. J. M. , Smit C. J.
Published: September 2010

Electroreduction of carbon dioxide in acetonitrile in the presence of butadiene gives rise to the formation of 3‐pentenoic acid (2), 3‐hexenedioic acid (3), and 3,7‐deca‐dienedioic and two isomeric C10‐dicarboxylic acids (4) in high chemical yields.