bluuebunny/crossref_metadata_2025 huggingface dataset:
Potential carcinostatics V. Synthesis and properties of potential inhibitors of the adenylosuccinate synthetase and adenylosuccinate lyase system
Authors: Wanner M. J. , van Wijk E. M. , Koomen G. J. , Pandit U. K.
Published: September 2010

β,β‐Dimethylaspartic acid was obtained by the aluminium‐amalgam reduction of the O‐methyloxime of diethyl 2‐oxo‐3,3‐dimethyl‐1,4‐butanedioate and subsequent hydrolysis. The (latter) diester was conveniently prepared by the condensation of ethyl 2‐bromo‐2‐methylpropionate with diethyl oxalate, under the influence of magnesium. β,β‐Difluoroaspartic acid, threo β‐methylaspartic acid and β,β‐dimethylaspartic acid (as racemates) were coupled with 6‐chloropurin‐9‐yl riboside to yield the corresponding nucleosides. The bases methyl 7‐oxo‐7H‐pyrido[2.1‐i]purine‐9‐carboxylate and 6‐[2,3‐bis(methoxycarbonyl)propyl]purine were converted into the corresponding nucleosides by coupling with O2,O3,O5‐tribenzoylribofuranosyl chloride and removal of the protecting groups. The biological test results on leukemia P‐388 are presented.
(2 + 2)‐Cycloaddition of o‐quinones to N,N‐dialkyl‐3‐alken‐1‐ynyl‐1‐amines. Thermal or photochemical ring closure of the adducts to 2H‐1‐benzopyran derivatives
Authors: Verboom W. , George A. V. E. , Brandsma L. , Bos H. J. T.
Published: September 2010

Addition of 9,10‐phenanthrenequinone or 3,5‐di‐tert‐butyl‐o‐benzoquinone to N,N‐dialkyl‐3‐alken‐1‐ynyl‐1‐amines R2‐CHCH‐C≡C‐NR12 (4) gives quinoid α‐alkenyl‐γ‐oxo‐α,β‐unsaturated carboxamides 6 or 8, respectively; these undergo a spontaneous ring‐closure, or can be cyclised photochemically into 2H‐phenanthro[9,10‐b]pyran‐4‐carboxamides 7 or 2H‐1‐benzopyran‐4‐carboxamides 9.
Addition/elimination reactions of an α‐tosyl substituted sulfine with nucleophilic reagents
Authors: van der Leij M. , Strijtveen H. J. M. , Zwanenburg B.
Published: September 2010

Oxidation of methyl 2‐methyl‐2‐p‐(tolylsulfonyl)propanedithioate with m‐chloroperbenzoic acid furnished the corresponding sulfine p‐MeC6H4SO2CMe2C(SO)SMe (2). This sulfine that bears a leaving group at its α‐carbon atom has especially been designed to investigate the possibility of a thiophilic addition with a concurrent elimination reaction upon treatment with nucleophilic reagents. Attempts to prepare the sulfine p‐MeC6H4SO2CMe2C(SO)Ph were unsuccessful. Reaction of sulfine 2 with MeOH/Et3N (or EtOH/Et3N) gave α‐methylthio‐α,β‐unsaturated sulfinates Me2CC(SMe)S(O)OMe (or Et) (10, 11). α‐Functionalized carbanions (α‐sulfonyl, α‐oxo or α‐cyano) also gave an addition‐elimination reaction to produce ketene dithioacetal monoxide derivatives (15–17). Similar products were obtained upon treatment with PhMgBr, PhCH2MgBr or MeLi. Evidence is presented that the thiophilic addition and the elimination of sulfinate take place synchronously.
Sulphur participation in cyclization reactions
Authors: de Loos Walter A. J. , van den Berg‐van Kuijk Anne J. W. , van Iersel Hans M. , de Haan Jan W. , Buck Henk M.
Published: September 2010

Cyclization initiated by thiiranium ions was investigated. Cis‐fused decalins were formed by a process involving inversion. In nitromethane a sulphonium salt 8 was formed. The reactions of 8 with nucleophilic reagent deviated from those of comparable compounds. It is expected that a product‐controlled transition state accounts for this feature.
Synthesis of fragments of human β‐lipotropin, βh‐LPH. Part III. The synthesis of des‐1‐tyrosine‐γ‐endorphin, i.e. β‐LPH‐(62‐77)
Authors: Greven H. M. , Bijl W. A. A. J. , van Nispen J. W.
Published: September 2010

The synthesis of the hexadecapeptide des‐1‐tyrosine‐γ‐endorphin, i.e. β‐LPH‐(62‐77), by means of the fragment condensation approach, is described. According to De Wied and co‐workers, this peptide, or a closely related one, may function as an endogenous neuroleptic.
A simple approach to 12‐azaprostaglandin congeners
Authors: Armande J. C. Lapierre , Pandit U. K.
Published: September 2010

The base‐catalyzed alkylation of N‐acylated 3‐pyrrolines has been studied. The reaction has been utilized in an approach to the synthesis of 12‐azaprostaglandins according to the following sequence. 3‐Pyrroline was acylated with 1‐chloro‐1‐octen‐3‐one and the resulting amide alkylated at the 2‐position with I‐(CH2)6C(OCH3)3. Subsequently, the α‐ and β‐(13,14‐dihydro)‐prostanoid chains were formed by sodium borohydride reduction, followed by hydrolysis. The resulting product, 1‐(3‐hydroxyoctyl)‐2‐(6‐methoxycarbonylhexyl)‐3‐pyrroline (13), constitutes a central intermediate for 12‐azaprostaglandins.
The photosensitized oxidation of a 19‐norsteroid: 11 β‐chloro‐17α‐19‐norpregn‐4‐en‐20‐yn‐17‐ol
Authors: Schönemann K. H. , van Vliet N. P. , Zeelen F. J.
Published: September 2010

Photosensitized oxygenation of 11β‐chloro‐17α‐19‐norpregn‐4‐en‐20‐yn‐17‐ol yields, aft́er reduction of the initially formed hydroperoxides, 11β‐chloro‐17α‐19‐norpregn‐3‐en‐20‐yne‐5α,17‐diol as the major product and 11β‐chloro‐17α‐19‐norpregn‐5‐en‐20‐yne‐4β,17‐diol as a minor product.
Photochemical hydroxylation of 7,8‐dimethylalloxazine (lumichrome). Structure elucidation of the irradiation product
Authors: te Nijenhuis B. , Mulder A. C. , Berends W.
Published: September 2010

The synthesis of 8‐methoxy‐3‐(methoxycarbonyl)‐6,7‐dimethyl‐2‐(methylamino)quinoxaline is described. The synthesized compound appeared to be identical with the product obtained by degradation of the irradiation product of lumichrome. From this the conclusion is drawn that the irradiation product of lumichrome in water is 9‐hydroxylumichrome.
The molecular structure of 6‐(bromomethyl)‐1,2,4‐trichloro‐3‐ethoxy‐3,7,7‐trimethoxybicyclo[2.2.1] heptane; an X‐ray study
Authors: Lenstra A. T. H. , van de Mieroop W. , Geise H. J. , van Bree J. , Anteunis M.
Published: September 2010

Hydrolysis of 6‐(bromomethyl)‐ 1,2,4‐trichloro‐3,7,7‐trimethoxybicyclo[2.2.1] hept‐2‐ene with perchloric acid in aqueous ethanol yields inter alia the title compound. X‐ray analysis proved the positioning of the substituents to be 6‐endo‐(bromomethyl)‐2‐endo‐chloro,3‐endo‐ethoxy, which is evidence that the addition in this case follows an endo‐tram mechanism.

The title compound crystallizes in the monoclinic space group P21/n with a = 10.504 Å, b = 10.507 Å, c = 15.783 Å, γ = 92.20° and Z = 4. The structure was solved by conventional techniques to an R = 0.063 using Mo(Zr) diffractometer data. The effect of the substitution on the conformation of the norbornane skeleton is discussed, as well as the geometry of the acetal groups in terms of the anomeric effect.
MCSCF and CI calculations of the dipole moment of cyclopropene
Authors: van Lenthe Joop H. , Smits Jos L. M.
Published: September 2010

Hartree‐Fock calculations lead to a dipole moment of cyclopropene opposite to that derived from experiments. We present MCSCF and CI calculations performed on a split valence basis set level in order to investigate the influence of correlation. Since the MCSCF and CI results scarcely differ from the Hartree‐Fock results, we conclude that the theoretically assigned polarity is the correct one.
Conformational equilibria of 3‐(cis‐styryl)phenanthrene and some benzologues
Authors: Somers J. B. M. , Laarhoven W. H.
Published: September 2010

An NMR investigation of cis and trans isomers of styrylphenanthrene and some benzologues was performed, in which Δtrans‐cis values (δtrans‐δcis), temperature dependence (ΔT) in CS2 and ASIS effects were determined. It was concluded that in the series styryl‐phenanthrene (2),‐benzo[c]‐phenanthrene (1),‐dibenzo[c,g]triphenylene (10),‐hexahelicene (9) only 1 exists mainly as a cis‐synrotamer, whereas in the other compounds the cis‐anti rotamer predominates in varying degrees. The introduction of an additional benzo group in 1 and 2 at the ring, containing the styryl substituent, which leads to the styryl‐chrysene (11) and styryl‐benzo[c]chrysene (12), shifts the conformational equilibrium to the cis‐syn rotamer. The introduction of polar substituents at the para‐position of 2‐styrylbenzo[c]phenanthrene has only a small influence on the syn‐anti equilibrium. The observed effects are discussed.
Mechanism for the conversion of right‐handed DNA helices into the left‐handed isomers. Part II
Authors: Buck Henk , van Aken Dirk , van Lier Johan , Kemper Martin
Published: September 2010

A detailed mechanism is given for the isomerization of right‐handed DNA into left‐handed DNA.
An interesting substituent effect on the acid‐catalyzed skeletal rearrangement of seco‐homocubanes
Authors: Vankan J. M. J. , Klunder A. J. H. , Noordik J. H. , Zwanenburg B.
Published: September 2010

The acid catalyzed rearrangement of 1‐bromotetracyclo[4.3.0.02.503.8]nonan‐4‐one 1b has been studied. With aqueous HBr, the exclusive formation of 2,7‐dibromotricyclo[4.2.1.03.7]‐nonan‐4‐one 4b was observed. This structure was established by X‐ray analysis. The divergency in behaviour of seco‐homocubane 1b and its 9‐ethylene acetal derivative 1a towards acidic reagents reveals a directing effect of the 9‐ethylene acetal function on the skeletal rearrangement.
C‐Nitroso compounds. Part XXXIII. Reaction of α‐chloronitrosoadamantane with Grignard reagents
Authors: Schenk C. , Beekes M. L. , de Boer Th. J.
Published: September 2010

The reaction of α‐chloronitrosoalkanes with aliphatic and aromatic Grignard reagents RMgX has been studied using the model compound α‐chloronitrosoadamantane (AdClNO)1. In addition to adamantanone oxime 7 (4‐60%) and the adamantanone oxime ether 8 (trace −28%), the expected nitrone 2 is formed. The nitrone can be isolated for synthetic purposes using a non‐ chromatographic procedure in widely varying yields ( 6 87 %). The structure of all nitrones has been determined using spectroscopic techniques.

Formation of oxime and oxime ether has been explained with the mechanism outlined in Scheme 3. This also accounts for the drastic changes in product distribution with the nature of the Grignard reagent. The mechanism involves nitrone formation via polar 1,2‐addition of the Grignard reagent to the nitroso group, and single electron transfer (SET) from the Grignard reagent to the nitroso compound which leads to an iminoxy radical together with radical R*. The latter combines with the multident iminoxy radical on nitrogen and oxygen (not on carbon) producing the nitrone and the oxime ether. Disproportionation can result in the formation of oxime. The oxime can also be formed when iminoxy radicals accept an electron from the Grignard reagent.

As the electron donating power is strongly influenced by the nature of the Grignard reagent (i.e. SET vs. polar addition), widely varying product distributions are obtained. The phenyl Grignard reagent is amongst the poorest of electron donors, and therefore gives almost exclusively nitrone by polar 1,2‐addition.

Since nitroso compounds are normally excellent free radical scavengers, it is difficult to explain why trapping of transient radicals R* by the nitroso compound, followed by loss of halogen, appears to be relatively unimportant as a route to nitrone (Scheme 3, reaction iii). The formation of dibenzyl (42%) from the reaction of AdClNO 1 with benzylmagnesium bromide is equally remarkable.
Recherches en série triazépine XVI.Condensation des composés β‐dicarbonylés avec les thiosemicarbazides
Authors: Hasnaoui A. , Lavergne J.‐P. , Viallefont Ph.
Published: September 2010

Condensations of β‐dicarbonyl compounds with thiosemicarbazide and 1‐ and 2‐methylthiosemicarbazide give three types of heterocyclic compounds. Depending upon the reagents and experimental conditions, triazepinones, triazepines, 1,2,4‐triazolines or pyrazoles are formed. Mechanisms explaining these cyclisations are proposed.
A convenient synthesis of specifically substituted conjugated dienes via organocopper(I) induced SN2′ reactions. An attractive route to myrcene
Authors: Kleijn H. , Westmijze H. , Meijer J. , Vermeer P.
Published: September 2010

The paper describes the preparation of a number of symmetrically substituted 1,3‐dienes H2C=C(R)‐C(R)=CH2 (3a‐d) as well as non‐symmetrically substituted 1,3‐dienes H2C=C(R1)‐C(R)=CR2R3 (3e‐i, R ≠ R1) by means of organocuprate induced SN2′ reactions in the esters X‐CH2‐C≡C‐CH2‐X (1, X = MeS(O)O or ToS‐O) and MeS(O)‐O‐CH2‐C(R1)=C=CR2R3 (4) respectively. An attractive application of the method is the easy preparation of the natural compound myrcene from 4 in which R1, R2 and R3 are hydrogen. A mechanistic rational for the reactions is discussed.
Studies on polypeptides XXXIII: Semisynthetic Ribonuclease analogues. The role of histidine‐119
Authors: Serdijn J. , Hoes C. , Raap J. , Kerling K. E. T.
Published: September 2010

As part of a structure‐activity relationship study of ribonuclease, focussing on the role of histidine‐119 in the active centre, two tetradecapeptides were synthesized by the solid‐phase method: [His119]RNase 111‐124 and the corresponding analogue in which His‐119 is replaced byL homohistidine.

While the [Hhis119] analogue has almost the same binding capacity towards RNase 1‐118 protein as the natural peptide, the resulting complex is devoid of any catalytic activity when RNA or 2′,3′‐CMP is used as substrate.
Synthesis of racemic 3‐hydroxy‐N‐methyl‐6‐oxomorphinan (Chemistry of opium alkaloids, Part XIV)
Authors: Olieman C. , Nagelhout Ph. , de Groot A. D. , Maat L. , Beyerman H. C.
Published: September 2010

The preparation of racemic 3‐hydroxy‐N‐methyl‐6‐oxomorphinan (5) by acid‐catalysed cyclization of 1‐(4‐hydroxybenzyl)‐1,2,3,4,5,8‐hexahydro‐6‐methoxy‐2‐methylisoquinoline (4) and its 4′‐methyl ether 6 is described. The corresponding N‐formyl derivatives did not give the desired cyclization.
ZnCl2‐catalysed cycloadditions between ketene acetals and α,β‐unsaturated carbonyl compounds. A simple route to 2,2‐dialkoxy‐3,4‐dihydropyrans
Authors: Bakker C. G. , Scheeren J. W. , Nivard R. J. F.
Published: September 2010

2,2‐Dialkoxy‐3,4‐dihydropyrans (3) can be obtained under mild conditions and in good yields from ketene acetals (1) and α,β‐unsaturated carbonyl compounds (2) in the presence of ZnCl2. At low temperatures (< −20°C) the reaction between1and2proceeds as a (2 + 2)‐cycloaddition, leading to an oxetane (4), which can sometimes be isolated by neutralisation of the Lewis acid. At higher temperatures, however, the oxetanes decompose into the starting compounds, eventually leading to the thermodynamically more stable dihydropyrans. The cycloadditions of tetramethoxyethene (1a) with2, having no substituents at the β‐carbon atom, yield a cyclobutane derivative as the low temperature product; in cycloadditions of α,β‐unsaturated esters this is the final product. Cycloadditions of 2‐chloroketene acetal (1e) lead in some cases to 2:1 adducts. The deviating behaviour of1aand1eis discussed.
Transthallation of anisole and chlorobenzene by phenylthallium(III) bis(trifluoroacetate)
Authors: Kooyman E. C. , Huygens A. V. , de Lepper J. P. J. , de Vos D. , Wolters J.
Published: September 2010

Phenylthallium(III) bis(trifluoroacetate) (PhTlX2) reacts with excess of anisole at 70‐80°, yielding mainly the three isomeric anisylphenylthallium(III) compounds (o‐, m‐, p‐AnPhTlX). Monoanisylthallium(III) derivatives (o‐, m‐, p‐AnTlX2) are obtained only in the presence of excess of HX. The slow transthallation reaction of chlorobenzene requiring the presence of HX leads to the o‐, m‐, p‐ClC6H4TlX2 isomers rather than to diarylthallium(III) compounds. The three isomeric anisylphenylthallium(III) compounds (o‐, m‐, p‐AnPhTlX) readily undergo exchange and isomerization reactions with anisole in the presence ‐ or more slowly in the absence ‐ of HX. Similar processes were observed with chlorobenzene but only in the presence of HX. (p‐Chlorophenyl)phenylthallium(III) trifluoroacetate is much less reactive, both towards anisole and chlorobenzene. With long reaction times the systems approach equilibrium distributions, which are approximately the same as those found for the prolonged direct thallation of the aromatic compounds. Tentative mechanistic interpretations include three different modes of formation of arylthallium bonds and draw a parallel between thallation, mercuration and plumbylation.
Etude des spectres de masse des thiocétones cyclaniques et α‐cyclaniques; mécanismes des fragmentations
Authors: Paquer D. , Morin L. , Vazeux M. , Andrieu C. G.
Published: September 2010

Twenty five cyclic and α‐cyclic thioketones were examined by mass spectrometry. Compared with the oxygen analogues, the thioketones yielded a higher proportion of molecular ions. The loss of •SH was found to be a characteristic fragmentation of cyclic and α‐cyclic thioketones as for aliphatic thioketones.
Empirical force field calculations VIII The interconversion of all‐cis‐1,2,3,4,5,6‐hexamethylcyclohexane
Authors: van de Graaf B. , Baas J. M. A. , Widya H. A.
Published: September 2010

The calculation of the enthalpy of activation for the interconversion of the equi‐energetic chair conformers of all‐cis‐1,2,3,4,5,6‐hexamethylcyclohexane (1), using five empirical force fields, gives rather poor results. A sizable negative entropy of activation, indicated by the calculations, can only partly compensate for the differences between experimental and calculated values of the free enthalpy of activation. Comparison of individual strain components with similar data for cyclohexane indicates the importance of the non‐bonded interactions for the interconversion barrier. The barriers for the chair‐chair interconversions of cyclohexane and 1 should be included in future force field parametrizations.
A quantum‐chemical model description for the function of cyclic AMP. Its degradation and activation of protein kinase
Authors: van Ool Peter J.J.M. , Buck Henk M.
Published: September 2010

CNDO/2 calculations were performed on pentaco‐ordinated phosphorus intermediates which are involved in the reaction of c‐AMP.
Electronic spectra and a theoretical study of the quinolizinium cation and the bromoquinolizinium cations
Authors: Párkányi Cyril , Sanders Georgine M. , van Dijk Marinus , Havinga E.
Published: September 2010

The PPP (Pariser‐Parr‐Pople) method has been used to study the quinolizinium ion (1) and the four isomeric bromoquinolizinium ions (2–5). The results have been used to interpret their electronic absorption and emission (fluorescence, phosphorescence) spectra. Also, predictions concerning the chemical reactivity of these compounds have been made and compared with the available experimental data.
Conformational equilibria of (E)‐6‐bromo‐7‐hydroxy‐3,7‐dimethyl‐2‐octene
Authors: van Dommelen M. E. , van de Ven L. J. M. , Buck H. M. , de Haan J. W.
Published: September 2010

The 1H NMR spectral parameters of the title compound have been determined in cyclohexane‐d12 and p‐dioxane‐d8 solutions by means of high‐frequency NMR. The results are interpreted in terms of conformational equilibria.

Linear Electric Field (LEF) effects may play a major role in explaining the differences between the 13C NMR chemical shifts of the title compound and those of the model (E)2,6‐dimethyl‐2,6‐octadiene. Some preliminary calculations of the LEF‐induced shifts are presented, as well as the problems involved in the recognition of the LEF contributions to the experimental shift differences.
A convenient synthesis of 2′‐O‐acetal‐N2‐acyl derivatives of riboguanosine
Authors: Verdegaal C. H. M. , Jansse P. L. , de Rooij J. F. M. , Veeneman G. , van Boom J. H.
Published: September 2010

The partially protected and crystalline 2′‐O‐levulinoyl‐3′5′‐O‐(tetraisopropyldisiloxane‐1,3‐diyl)guanosine derivative (4) serves as a key intermediate for the synthesis of 2′‐O‐acetal‐N2‐acylriboguanosines 1c. Acylation of 4 with diphenylacetic anhydride gave, after hydrazinolysis of the levulinoyl group, the N2‐acyl derivative 6 in high yield. Acylation of 4 with benzoyl or biphenyl‐4‐carbonyl chloride afforded the corresponding N2‐acyl derivatives in lower yields. Acetalization of derivatives 6 with 4‐methoxy‐5,6‐dihydro‐2H‐pyran, followed by the removal of the 1,1,3,3‐tetraisopropyldisiloxane‐1,3‐diyl (TIPS) group, gave the corresponding 2′‐O‐acetal‐N2‐acylriboguanosines 1c.
The meta‐photocycloaddition of cyclopentene to ortho‐methylanisole
Authors: Jans A. W. H. , Cornelisse J.
Published: September 2010

Photocycloaddition of cyclopentene to ortho‐methylanisole yields two products. The addition takes place at the positions ortho with respect to the methoxy group.
Mechanism of the vapour‐phase dehydrogenation of methanol on silver
Authors: Aneke L. E. , den Ridder J. J. J. , van den Berg P. J.
Published: September 2010

The dehydrogenation of methanol to formaldehyde in the absence of oxygen on a silver catalyst has been studied in a pulse system. The results suggest that the reaction is initiated on the surface of the catalyst, and that the formation of formaldehyde proceeds homogeneously in the gas phase. Formaldehyde yields per pass of more than 40% were obtained at 670°C with a contact time of 0.001 sec.
Réactions d'addition nucleophile sur les cétones. Influence de l'environnement stérique sur la position de l'état de transition
Authors: Boyer B. , Lamaty G. , Moreau C.
Published: September 2010

In the present investigation, we have measured the secondary kinetic deuterium isotope effects in hydroxylamine addition reaction for a series of cyclohexanones, both hindered and unhindered. We observed a slightly direct isotope effect, kH/kD > 1.00, for unhindered cyclohexanones and an inverse isotope effect, kH/kD < 1.00, for hindered cyclohexanones; this inversion of the isotope effects is attributed to a decrease of the torsional strain through the intervention of an “effet stérique de compression” that induce a slight deformation of the cycle and changes the angle of approach of the nucleophile.
Chemical synthesis of a 5′‐ and 3′/2′‐phosphorylated heptamer sequence of E. coli tRNA: pAGCCUGG(3′/2′)p via phosphotriester methods
Authors: den Hartog J. A. J. , van Boom J. H.
Published: September 2010

The synthesis of the 5′‐ and 3′/2′‐phosphorylated heptamer sequence pAGCCUGG(3′/2′)p, corresponding to the fragment 14–20 of E. coli tRNAfmet, is described. The assemblage of the fully protected heptamer 16 was effected via a modified phosphotriester approach which is based on the use of the monofunctional phosphorylating agent, 2,2,2‐trichloroethyl 2‐chlorophenyl phosphorochloridate (3). Thus, various suitably protected building blocks were prepared which were phosphorylated with 3 on the 3′‐hydroxyl function (e.g. compounds 4 and 5). For the introduction of the 5′‐ and 3′/2′‐phosphate functions, two terminal building blocks were synthesized; one with, inter alia, a 5′‐O‐(phenyl benzyl phosphoroamidate) function (8) and another with 2′‐O‐(diphenyl phosphate) and 3′‐O‐propionyl groups (10). The latter intermediates (i.e. compounds 4, 5, 8 and 10) were assembled to give the fully protected heptanucleotide (16). Complete deprotection of 16 by base and acid treatment gave the required heptamer.
The chemistry of small ring compounds. Part 45 Thermolysis and photolysis of l‐(alkylthio)cyclopropyl azides
Authors: Jorritsma R. , Steinberg H. , de Boer Th. J.
Published: September 2010

1‐(Alkylthio)cyclopropyl azides ‐ readily accessible from the corresponding chlorides and bromides ‐ are smoothly decomposed at 70°C with nitrogen evolution. The main process is a ring enlargement to 2‐(alkylthio)azetines 2, accompanied by cleavage to thiocyanate and alkene. Reaction parameters for the thioazetine formation suggest a two‐step mechanism involving an intermediate cyclopropylnitrene. Ring enlargement can be averted if the alkylthio group contains a double bond. Thus, the allylthiocyclopropyl azide 8 gives a nitrene that can interact not only with the three‐membered ring but also with the double bond, leading to spirocyclic products (15 and 16 in Scheme 1). The photolysis (300 nm) of these azides gives exclusively the fragmentation products thiocyanate and olefin.
An efficient synthesis of 3‐arylpiperidines
Authors: Loozen H. J. J. , Brands F. T. L.
Published: September 2010

An alternative route to 3‐arylpiperidines is described, thereby circumventing traditional Michael addition of substituted phenylacetonitriles to methyl acrylate. Treatment of (3‐methoxyphenyl)acetonitrile (2) with the THP ether of 3‐bromo‐1‐propanol, followed by chromic acid oxidation and saponification provided 2‐(3‐methoxyphenyl)glutaric acid (6). Treatment of the corresponding anhydride 7 with alkyl‐ and arylalkylamines provided the imides 8a‐c. Replacement of the methoxy group by a benzyloxy group, followed by LiAlH4 reduction and a catalytic reduction provided 1, 12 and 13.
A study of the reactions of 1,3‐diynes with organo‐cuprates and ‐argentates
Authors: Kleijn H. , Tigchelaar M. , Meijer J. , Vermeer P.
Published: September 2010

1,3‐Diynes HCCCCR′ (1, R′  H or Ph) are converted by cuprates [RCuY]M′ (R  alkyl; Y  Cl, Br or R; M′  Li, MgCl or MgBr) into a mixture of [HC(CuY)C(R)CCR′]M′ (2) and [RCHC(CuY)CCR′]M′ (3). When R is n‐alkyl, adducts2are the major products; adducts3are preferentially formed when R is a branched alkyl. Organoargentates [RAgY]MgCl (R  alkyl, Y  Br or R) convert diynes1selectively into [RCHC(AgY)CCR′]MgCl (6). The latter regiospecific reaction has been used to prepare functionally substituted enynes RCHC(E)CCR′ (7: E  Br, I, allyl, CO2H) in good yields.
Chemistry of ketene acetals IV. A simple and general method for the preparation of 4‐hydroxy‐γ‐butyrolactones and 2‐butenolides from 1,1‐dimethoxypropene and α‐acyloxy aldehydes and ketones
Authors: Aben R. W. , Hofstraat R. , Scheeren J. W.
Published: September 2010

α‐Acyloxy aldehydes (2a,b) react with 1,1‐dimethoxypropene (1) in the presence of ZnCl2 to yield 2,2‐dimethoxy‐3‐methyloxetanes (3a,b). Stronger electron‐withdraxing acyl groups are necessary for the analogous conversion ofα‐acyloxy ketones (2c,d,e). Hydrolysis of the acyloxy group with potassium hydroxide yields the corresponding hydroxyoxetanes (4) which rearrange under neutral or weakly acidic conditions to 2,2‐dimethoxy‐3‐methyl‐4‐hydroxytetrahydrofurans (5). By mild acidic hydrolysis of 5, the corresponding γ‐butyrolactores (6) are obtained in moderate to good yields. Treatment of 6 with concentrated sulfuric acid yields 3‐methyl‐2‐(5H)‐furanones (3‐methylbutenolides, 10).
Synthesis of the self‐complementary RNA‐DNA hybrid:R(GCG)D(TATACGC)
Authors: van Boeckel C. A. A. , van der Marel G. A. , Wille G. , Westerink H. , Wang A. H. J. , Mellema J. R. , Altona C. , van Boom J. H.
Published: September 2010

A nucleic acid fragment containing a RNA trimer and a DNA heptamer wich are linked by a 3′‐5′‐internucleotide phosphodiester bond has been synthesized by a phosphotriester approach. The sequence of the nucleosides is such that they will form a self‐complementary double‐helical fragment which may serve as a probe to get more insight into the process of discontinuous DNA replication.
Synthesis of α,β‐γ,δ‐unsaturated sulfones and sulfoxides via the Horner‐Emmons reaction
Authors: de Jong B. E. , de Koning H. , Huisman H. O.
Published: September 2010

α,β‐γ,δ‐Unsaturated sulfones and sulfoxides have been prepared via the Horner‐Emmons reaction of α,β‐unsaturated carbonyl compounds with α‐phosphoryl sulfones and sulfoxides.
Addition of dithio esters and trithiocarbonates to 1‐(diethylamino)propyne. Formation of α, β‐unsaturated thioamides and vinylogous thioamides
Authors: Elferink V. H. M. , Visser R. G. , Bos H. J. T.
Published: September 2010

α,β‐Unsaturated thioamides and vinylogous thioamides have been prepared by thermal addition of trithiocarbonates RS‐C(S)SR1 to 1‐(diethylamino)propyne. Aromatic dithio esters Ar‐C(S)SR only gave the α,β‐unsaturated thioamides. The dithio ester Me2CH‐C(S)SMe adds as acidic enethiol tautomer Me2CC(SH)SMe to 1‐(diethylamino)propyne. Reaction mechanisms and the stereochemistry of the adducts are discussed.
Replacement of hydrogen fluoride in solid phase peptide synthesis by methanesulfonic acid
Authors: van Nispen J. W. , Polderdijk J. P. , Janssen W. P. A. , Greven H. M.
Published: September 2010

The dangerous liquid HF, which in addition causes many side‐reactions, has successfully been replaced by the easy‐to‐handle organic acid methanesulfonic acid for the cleavage of small peptides from the standard Merrifield resin.
Reactions of tert‐butylsulfinyl chloride with tert‐butyl hydroperoxide and tert‐butyl hydrodisulfide in the presence of pyridine. Observation of 1H CIDNP effects
Authors: Bleeker Ido P. , Engberts Jan B. F. N.
Published: September 2010

tert‐Butylsulfinyl chloride (1) reacts smoothly with tert‐butyl hydroperoxide (2) in the presence of pyridine to afford a variety of products including pyridinium tert‐butylsulfonate, tert‐butyl tert‐butylthiolsulfonate, tert‐butanol and tert‐butylsulfonyl chloride. The mechanistic pathway most likely involves homolytic cleavage of the initially formed tert‐butyl tert‐butyl‐peroxysulfinate (5) via a radical cage process. 1H CIDNP effects provide strong evidence in support of the radical pair mechanism. The homolytic dissociation of 5 contrasts with the preferred heterolytic cleavage of peroxysulfonates.

Under similar reaction conditions, 1 reacts with tert‐butyl hydrodisulfide (3) to afford tert‐butylsulfinyl tert‐butyldisulfide (13) in a yield of 90%. As compared with 5, thermal decomposition of 13 is much slower, reflecting the higher SOS bond dissociation energy in 13, relative to the low OO bond dissociation energy in 5. At elevated temperatures, 13 yields tert‐butyl tert‐butylthiolsulfonate and di‐tert‐butyl tetrasulfide, probably via a homolytic pathway.
Synthesis and photochemical reactivity of bilirubin model compounds
Authors: de Groot J. A. , van der Steen R. , Fokkens R. , Lugtenburg J.
Published: September 2010

The bilirubin model compounds 1, 2 and 3 were prepared in good yield. The photochemistry of 1, 2 and 3, which all have the 4Z,15Z form, was investigated; they show a Z‐E isomerisation to the 4Z,15E and the 4E,15E isomers. Unlike the isomers of 1, those of the compounds 2 and 3, could be isolated in a pure form.
Photochemistry of chloro‐2‐vinylstilbenes
Authors: Op den Brouw P. M. , Laarhoven W. H.
Published: September 2010

Short irradiation at 300 nm of α‐chloro‐ and β‐chloro‐2‐vinylstilbene (20 and 21) leads to a mixture of 2‐vinyltolane (35) and 2‐vinylstilbene (1) accompanied by the cis‐ and trans‐isomers of the starting compounds. Evidence is found for the occurrence of an ionic intermediate during the photolysis of 20 in methanol. At 360 nm, an additional, small amount of 1‐chloro‐endo‐ and 1‐chloro‐exo‐6‐phenylbenzobicyclo[3.1.0]hex‐2‐ene (39) is formed from 20. The elimination of hydrogen chloride also occurs during the irradiation of 2‐(2‐chlorovinyl)stilbene (23) and leads to 2‐ethynylstilbene (41). The acetylenic compounds are photocyclized into 2‐phenylnaphthalene (38). However, 2‐(1‐chlorovinyl)stilbene (22) reacts without loss of chlorine to give 1‐chloro‐exo‐5‐phenylbenzobicyclo[2.1.1]‐hex‐2‐ene (40). This exceptional reaction mode is due to a much higher rate of photocyclization resulting from less distortion in the stilbene moiety and a preference for a conformation better suited to the reaction of the 2‐(1‐chlorovinyl)stilbene molecule. It is shown that both isomers of 22 can photocyclize into 40.
Palladium(0)‐catalysed conversion of α‐acetylenic epoxides into α‐allenic alcohols. Novel route to (±)‐2,3‐octadiene‐5,7‐diyn‐1‐ol, a metabolite from fungus Cortinellus berkeleyanus
Authors: Kleijn H. , Meijer J. , Overbeek G. C. , Vermeer P.
Published: September 2010

α‐Acetylenic epoxides,R′CCCR″CH2 (1), have been converted into α‐allenic

alcohols, RR′CCCR″‐CH2OH (3), by means of a palladium(0)‐promoted reaction with R‐ZnCl (2; R: Me3Si(C≡C)n‐(n=1 or 2), H2CCH‐ or t‐BuCHCCH‐). Using this method, an improved synthesis of (±)‐2,3‐octadiene‐5,7‐diyn‐1‐ol, a metabolite from fungus Cortinellus berkeleyanus, has been developed. The method is not suited to the preparation of α‐allenic alcohols from 1 and, for example, BuZnCl because of substantial formation of reduction products, HCR′CCR″‐CH2OH. For the preparation of 3 from R = Me3SiC≡C other acetylides Me3SiC C‐M were also studied, viz. M = Li, MgCl, Cu or Cu1/2Li1/2 but only with the cuprate could a reasonable conversion of 1 be realized.
A model study of the role of the CONH2‐group in the redox Co‐enzyme NAD(P)+‐NAD(P)H
Authors: van Lier P. M. , Donkersloot M. C. A. , Koster A. S. , van Hooff H. J. G. , Buck H. M.
Published: September 2010

A model is offered for the role of the CONH2‐group in the stereospecific incorporation of hydride at C(4) in NAD(P)+‐like compounds.
Solid‐phase synthesis of the RNA fragment: rAAGAAGAAGAAGA
Authors: van der Marel G. A. , Wille G. , van Boom J. H.
Published: September 2010

The synthesis of the tridecaribonucleotide AAGAAGAAGAAGA on a polystyrene solid support via a phosphotriester approach is described. The assemblage of the oligomer was performed by four repeated coupling reactions of the partially protected trimer AAGp(3′) with an immobilized dimer in the presence of the activating agent (2,4,6‐triisopropylbenzenesulfonyl)‐3‐nitro‐1,2,4‐triazole. Purification of the RNA fragment was easily achieved by Sephadex G50 column chromatography.
Reaction of 1‐alkynyl thiocyanates with nucleophilic reagents. Synthesis of 2,4‐disubstituted 1,3‐thiazoles
Authors: de Jong R. L. P. , Meijer J. , Sukhai R. S. , Brandsma L.
Published: September 2010

Reaction of 1‐alkynyl thiocyanates RC≡C‐S‐C≡N (1) with alcohols, phenol or thiols or secondary aliphatic amines in the presence of anhydrous zinc chloride or boron trifluoride diethyl etherate gives mixtures of 2,4‐disubstituted 1,3‐thiazoles (2), thiocarbonyl compounds (3) (thiono esters, dithio esters or thioamides) and 2‐alkylidene‐1,3‐dithioles (4). In all cases, the 1,3‐thiazoles can be obtained in good yields if the proper reaction conditions are applied. Interaction between 1 and lithium dialkylamides LiNR′2 gives the compounds RC≡C‐S‐NR′2 (5) (attack on sulfur). With alkoxides R′O⊖, the primary attack is on C≡N•• the intermediary alkynethiolate RC≡C‐S⊖; subsequently reacts with the alkyl cyanate R′OC≡N to afford 1‐alkynyl sulfides RC≡C‐SR′ (6).
Experimental and calculated thermodynamic data for the isomeric methylcyclohexenes and methylenecyclohexane
Authors: Peereboom M. , van de Graaf B. , Baas J. M. A.
Published: September 2010

The equilibria in the isomerisation of the methylcyclohexenes and methylenecyclohexane have been investigated in the temperature range of 413 to 523 K. ΔrH and ΔrS have been calculated from the experimental data for the following equilibria: methylenecyclohexane ⇄ 1‐methylcyclohexene, 3‐methylcyclohexene ⇄ 1‐methylcyclohexene and 4‐methylcyclohexene ⇄ 1‐methylcyclohexene. The resulting values for ΔrH and ΔrS are respectively: 7.3 ± 1.7, 7.6 ± 0.5, and 6.7 ± 0.4 kJ mol−1 and −15.9 ± 0.3, 1.0 ± 1.6 and 1.5 ± 1.4 J mol−1K−1. These data are compared with values calculated using molecular mechanics.
Photoinduced long‐range electron transfer in rigid bichromophoric molecules
Authors: Pasman P. , Koper N. W. , Verhoeven J. W.
Published: September 2010

Fast excited‐state electron transfer is observed between two chromophores held apart by a rigid saturated steroid moiety.
Derivatives of m‐di‐tert‐butylbenzene. Part VII. 1H Nuclear magnetic resonance spectra of some sterically crowded halogenated aromatic compounds
Authors: de Koning Adrianus Jan
Published: September 2010

The 1H NMR spectra of seven series of halogenated derivatives of m‐di‐tert‐butylbenzene have been analysed. The results show that the hydrogen atom between the tert‐butyl groups is screened from the magnetic influence of the halogen atoms. The results also show that the effect of a halogen atom on the chemical shift of hydrogens ortho and meta to halogen is substantially reinforced by a tert‐butyl group buttressing the halogen.
Aromatic sulfonation 85. Halogen directing and steric effects in the sulfonation of the twelve halogenotoluenes and some related compounds
Authors: Cerfontain Hans , Koeberg‐Telder Ankie , Laali Khosrow , Lambrechts Hans J. A. , de Wit Peter
Published: September 2010

The isomer distributions for the sulfonation of the twelve halogenotoluenes and some trisubstituted halogenomethylbenzenes, with both 98.4% H2SO4 at 25°C and sulfur trioxide in nitromethane at 0°C, have been determined and found to be very similar. The predominantly para‐directing effect of the halogen substituent dominates over that of the methyl substituent: with the 2‐halogenotoluenes, the degree of 5‐substitution decreases from ≥90% for the fluoro to 50% for the iodo compound. The 2‐ to 3‐sulfonation ratio of the 4‐halogenotoluenes strongly increases on going from fluorine (0.5) to iodine (7). The ratio of the partial rate factors for the sulfonation of a halogenobenzene ortho and meta to halogen varies from 17 ± 1 for the fluoro to 1.5 ± 0.4 for the iodo substituent.

In competition to the sulfonation, 2‐ and 4‐iodotoluene undergo deiodination. The latter process is more important with the 4‐isomer and with the protic sulfonating reagent. With the aprotic reagent, the reaction proceeds by direct sulfodeiodination, whereas with the sulfuric acid reagent, it proceeds by initial protiodeiodination and subsequent sulfodeprotonation.
1H and 13C NMR spectra of mianserin and 10‐hydroxymianserin derivatives in solution. Spectral assignments and conformational conclusions
Authors: Funke Carel W.
Published: September 2010

The 1H and 13C spectra of mianserin, 1, reveal a perfectly chair‐formed piperazine ring having an equatorial N‐methyl group, a trans‐piperazine‐dihydroazepine ring junction and a nonplanar dihydroazepine ring. The 1H spectra of the 10‐hydroxymianserin derivatives 2 and 3 show that their dihydroazepine ring conformation is similar and that C(10) ‐ the upper bridge ‐ is twisted towards the N(5) lone pair.
Synthesis and properties of 2,2′‐pyrromethene‐5[1H]‐one analogues: The furan, thiophene, benzene, 4‐methoxybenzene, 2‐pyridine and 4‐pyridine analogues
Authors: de Groot J. A. , Jansen H. , Fokkens R. , Lugtenburg J.
Published: September 2010

Condensation of furfural, thiophene‐2‐carboxaldehyde, benzaldehyde, 4‐methoxybenzaldehyde, pyridine‐2‐carboxaldehyde and pyridine‐4‐carboxaldehyde with 3,4‐dimethyl‐3‐pyrrolin‐2‐one leads to the Z‐2,2′‐pyrromethene‐5[1H]‐one analogues. Following irradiation with light, the E forms have been isolated and characterized. Complete thermal E→Z isomerization is observed upon heating in basic methanol. On irradiation in non hydrogen‐donating solvents the analogues 3a, 3b and 3e show very little or no photoisomerisation due to the intramolecular hydrogen bond. Condensation of these aldehydes with 1,3,4‐trimethyl‐3‐pyrrolin‐2‐one gives mixtures of the corresponding Z‐ and E‐2,2′‐pyrromethene‐5[1H]‐one analogues. The Z and E forms both isomerise thermally upon heating in basic methanol to give the same equilibrium state as is observed during the synthesis. Upon irradiation with light, the compounds similarly undergo Z‐E isomerisation.
Bond dissociation energies in 2‐methoxy‐3‐phenylpropionitrile and in bibenzyl; capto‐dative stabilization of the cyano methoxy methyl radical
Authors: Louw Robert , Bunk Jaap Joosting
Published: September 2010

In the temperature region of 800–900K the rate of CC bond homolysis in 2‐methoxy‐3‐phenylpropionitrile (˜1a) is 2‐3 times faster than in bibenzyl (˜2a), from which it is inferred that the “capto‐dative” stabilization of the CH(OMe)CN radical is ca. 4 kcal/mol.
H NMR spectra of the fluorenyl and the 9‐methylfluorenyl anion
Authors: Maas J. A. S. , Kloosterziel H.
Published: September 2010

Introduction of a methyl group at C(9) of the fluorenyl anion changes the chemical shifts of the protons at C(2) and C(3) in opposing senses.
Intramolecular complexation in N,N′‐bis(2‐carbamoylethyl)‐diaza‐18‐crown‐6
Authors: van Zon A. , Coleman B. , Blaauw L. P. , Torny G. J. , Frijns J. H. G.
Published: September 2010

The 2‐carboamoylethyl side chains in 7,16‐bis(2‐carbamoylethyl)‐1,4,10,13‐tetraoxa‐7,16‐diazacyclooctadecane are shown by NMR to be preferentially complexed as in the anti conformation ˜2.
The complexation of calcium(II) and lanthanide(III) cations with the phosphate substitute (carboxymethoxy)succinate (CMOS), as studied by magnetic resonance spectroscopy
Authors: Vijverberg C. A. M. , Peters J. A. , Bovée W. M. M. J. , Vroon H. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

The complexation of trisodium (carboxymethoxy)succinate (Na3CMOS) with calcium(II) and with lanthanide(III) cations has been studied using NMR spectroscopy. Structural information has been obtained from lanthanide‐induced shifts (LIS), T1 relaxation rate enhancements and vicinal 1H coupling constants. CMOS forms 1:1 and 1:2 complexes in which it mainly acts as a tetradentate ligand via the three carboxylate groups and the ether oxygen. LIS measurements on non‐racemic mixtures of Na3CMOS indicate self‐association of the Ln(III) complexes at [CMOS]0 > 0.01 M.
A model for the transfer of conformational change in the phospholipid headgroup towards the hydrophobic interior of the membrane via a PV trigonal bipyramidal intermediate
Authors: Merkelbach Ingrid I. , Buck Henk M.
Published: September 2010

Co‐ordination change of phosphorus may be responsible for a decrease of the cross‐sectional area of the phospholipid headgroup and a reduction of the difference in effective chain length between both acyl chains of a phospholipid molecule. Both factors induce a change in the angle of tilt of the acyl chains, leading to increasing or decreasing lateral phase separation.
A migration process in some sulphur‐substituted cycloheptatrienes studied using saturation transfer NMR
Authors: Zwaard A. W. , Erkelens C. , Kloosterziel H.
Published: September 2010

Modified Forsén‐Hoffman experiments (in the FT mode) show that, in 7‐substituted cyclohepta‐1,3,5‐trienes benzenesulphonyl groups migrate in a random way, while phenylthio substituents show a specific 1,2‐migration. Activation parameters for the migration process are given for a number of compounds.
Photochemistry of dienones. Part 11. Photochemistry of the pivaloyl analogues of (E)‐α‐ and (E)‐β‐ionone
Authors: Visser Cornelis P. , van der Wel Hans , Cerfontain Hans
Published: September 2010

The photochemical reactions of 1b and 15b, i.e. the pivaloyl analogues of (E)‐α‐ (1a) and (E)‐β‐ionone (15a), have been examined. The replacement of the acetyl group in 1a by a pivaloyl group does not change the initial photoreactions up to the retro‐ionone stage, although beyond this stage a change is observed. The retro‐α‐ionone analogue 4b undergoes α‐cleavage, followed by decarbonylation and recombination of the resulting radicals. Irradiation of the retro‐γ‐ionone analogue 18b yields the tricyclic oxetane 19b and the decarbonylated product 22. The formation of 11 in the α‐series and of 22 in the β‐series is explained in terms of a photochemical [1,3]‐hydrogen shift in 10 and 21, respectively.
Chemistry of peroxyacyl nitrates. Part III. The oxidation of thioethers by peroxyhexanoyl nitrate
Authors: van Noort Paul C. M. , Vermeeren Hans P. W. , Louw Robert
Published: September 2010

The reaction of peroxyhexanoyl nitrate, 1a, a homologue of the atmospheric pollutant “PAN”, 1b, with some twenty thioethers, is described. At 0‐25°C, common thioethers such as Et2S or PhSMe are rapidly converted into sulfoxides in high yields in a variety of solvents, ranging from pentane and chloroform to acetic acid, methanol and aqueous acetonitrile. Rates are essentially solvent‐independent, although the reaction is subject to marked steric hindrance. Relative rates for five p‐substituted thioanisoles in MeOH at 22°C, leading to a Hammett ρ‐value of ‐1.7, show that the sulfur atoms display nucleophilic character. Electron‐attracting groups on α‐carbon, such as in PhSCCl3 and in MeSCH2OC(O)Ph, inhibit the formation of sulfoxide. Addition of EtSH lowers the yield of sulfoxide, producing instead EtSSEt and EtSNO. Oxidation of Me2S by 1a with the NO2 group labelled by 18O does not give rise to 18O‐enriched DMSO. Comparison of (CH3)2S with (CD3)2S revealed an inverse kinetic H/D isotope effect.

The products obtained from 1a vary with solvent. In the presence of water or EtSH, hexanoic acid is formed, while methanol gives rise to methyl hexanoate, and in pentane/hexanoic acid, hexanoic anhydride is produced. In aprotic solvents, significant amounts of CO2 are formed.

These observations can best be rationalized on the basis of an intermediate sulfurane R1R2S(ONO2)(OCOR), (I), produced from thioether R1SR2 and 1a, in the first step. The fate of I under various conditions is discussed.

Finally, the features of the oxidation of thioethers by peroxyacylnitrate are compared with those of acyl peroxides and peroxy esters. It is suggested that in each case formation of a sulfurane may well be the first step.
Chemistry of crown ethers. Part XXII. Synthesis and complexing properties of monophospha‐crown ethers
Authors: van Zon A. , Torny G. J. , Frijns J. H. G.
Published: September 2010

The synthesis of phenyl‐ and tert‐butyl‐phosphadibenzo‐18‐crown‐6 and phenylphosphadibenzo‐21‐crown‐7 is described. The complexation of alkali metal cations and rhodium(I) by these macrocycles and their phosphine oxides has been studied by NMR methods. The phosphorus crown ethers are all capable of solubilizing lithium cations into chloroform. The phosphine oxide macrocycles also solubilize sodium cations. It is remarkable that tert‐butyl‐phosphadibenzo‐18‐crown‐6 complexes the sodium cation, whereas phenylphosphadibenzo‐18‐crown‐6, whose cavity is about the same size, does not. The formation of a bimetallic (Rh(I),Li+) complex of phenylphosphadibenzo‐21‐crown‐7 is discussed.
Temperature dependence of the primary kinetic isotope effect for hydride transfer mediated by a NAD(P)H‐model; discrimination between bent and linear transition states
Authors: van Gerresheim W. , Verhoeven J. W.
Published: September 2010

Temperature dependence of the primary kinetic isotope effect for hydride transfer from 1‐benzyl‐1,4‐dihydronicotinamide (a NAD(P)H‐model) to the 10‐methyl‐9‐phenylacridinium ion conclusively shows the reaction to proceed through a linear transition state.
Photochemical ring contraction of 4‐heteroaryl‐substituted 1,4(or 3,4)‐dihydropyrimidines into imidazoles
Authors: van der Stoel R. E. , van der Plas H. C. , Jongejan H.
Published: September 2010

Photolysis of 4‐R‐1,4(or 3,4)‐dihydropyrimidines causes ring contraction into imidazoles, provided that the substituent R is capable of sufficiently stabilizing an anionic centre (R = 2‐thiazolyl, 2‐pyridyl, 4‐pyridyl). Chemical evidence is presented to show that the ring contraction of 6‐phenyl‐4‐(2‐pyridyl)1,4(or 3,4)‐dihydropyrimidine occurs via heterolytic fission of the C(1)‐C(6) bond of intermediate 1‐phenyl‐6‐(2‐pyridyl)‐2,4‐diazabicyclo[3.1.0]hex‐2(or 3)‐ene. The anion‐stabilizing effect of R is correlated with the acid strength (pKa) of R–CH3. A pKa value around 30 probably determines the border‐line between ring contraction into an imidazole and formation of an isomeric 5‐R‐1,2(or 2,3)‐dihydropyrimidine.
Polyelectrolyte surfactant complexes as improved models for esterolytic enzymes
Authors: Visser Hendrik G. J. , Nolte Roeland J. M. , Drenth Wiendelt
Published: September 2010

Cationic surfactants enhance the catalytic activity of imidazole containing polymers of isocyanides in the hydrolysis of activated esters.
Activation and activity of ruthenium on silica hydrogenation catalysts
Authors: Koopman P. G. J. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

Activation of RuCl3‐impregnated silica by hydrogen treatment at high temperature, up to 700°C, is superior to a procedure involving air calcination of the material prior to reduction. Upon direct reduction, sintering hardly occurs, whereas the Ru metal surface, as measured by hydrogen desorption, increases at higher activation temperature, due to the removal of chlorine impurities from the Ru surface. Activity measurements of the Ru catalysts for the liquid‐phase hydrogenation of benzene and cyclohexene reflect the favourable effect of the high‐temperature reduction of RuCl3/SiO2. Similar phenomena are observed for some PdRu/SiO2 catalysts.