bluuebunny/crossref_metadata_2025_split huggingface dataset:
Evidence for α‐lactone formation in the thioacetylation of some α‐hydroxy acids with the aid of Mitsunobu‐type reagent
Authors: Strijtveen Bert , Kellogg Richard M. 
Published: September 2010

Abstract(S‐Mandelic acid, (S)‐lactic acid, and (S)‐2‐hydroxy‐3‐phenylpropionic acid react with thioacetic acid in the presence of the salt of diisopropyl azodicarboxylate and triphenylphosphine to give the α‐(acetylthio)‐substituted products. (S)‐Mandelic acid reacts with predominant retention of configuration whereas (S)‐lactic acid and (S)‐2‐hydroxy‐3‐phenylpropionic acid react predominantly with inversion. The involvement of α‐lactone intermediates is very likely.
1,2,3‐Triarylpropenones as starting materials for 2‐pyridinethiones
Authors: Paniagua Esther , Rubio María J. , Seoane Carlos , Soto José L. 
Published: September 2010

Abstract2‐Pyridinethiones 3 are obtained in good yields from 1,2,3‐triarylpropenones 2 by treatment with cyanothioacetamide 1. Disulfides 4 result from oxydation of 3. Pyridinethiones 3 undergo methylation at the sulfur atom, leading to (methylthio)pyridines 5, which can be hydrolized to carboxamides 6. Thieno[2,3‐b]pyridines 7 are obtained from 3 upon reaction with methyl chloroacetate.
Synthesis of the antibiotic 1,5‐dideoxy‐1,5‐imino‐D‐glucitol; concomitant formation of the D‐mannitol analogue
Authors: Broxterman H. J. G. , van der Marel G. A. , van Boom J. H. , Neefjes J. J. , Ploegh H. L. 
Published: September 2010

AbstractThe easily accessible 1,2‐O‐isopropylidene‐3‐O‐benzyl‐α‐D‐glucofuranose was converted in six steps into 1,2‐O‐isopropylidene‐3,6‐di‐O‐benzyl‐5‐deoxy‐5‐azido‐α‐D‐glucofuranose. The latter afforded, after acidolysis followed by hydrogenolysis, 1‐deoxynojirimicine and a small quantity of 1‐deoxymannonojirimicine. The antibiotic thus obtained had an inhibitory effect on the trimming of N‐linked carbohydrates in IgM.
Synthesis of an analogue of the antithrombin binding region of heparin containing α‐L‐idopyranose
Authors: van Aelst S. F. , van Boeckel C. A. A. 
Published: September 2010

AbstractThe synthesis of a heparin‐like pentasaccharide, containing 2,6‐di‐O‐sulphated α‐L‐idopyranose instead of the naturally occurring 2‐O‐sulphated α‐L‐idopyranuronate, is described. Although conformational properties of these compounds are similar, the analogue is not biologically active.
Photochemistry of 2,5‐dialkyl‐1,3,5‐hexatrienes. The influence of the ground‐state conformation, controlled through steric substituent effects
Authors: Brouwer A. M. , Bezemer L. , Cornelisse J. , Jacobs H. J. C. 
Published: September 2010

AbstractThe photochemical reactions of a number of 2,5‐dialkyl‐1,3,5‐hexatrienes are described. Variations in the selectivity of the reactions are observed, which can be rationalized by considering differences in the composition of the equilibrium mixture of conformational isomers, brought about by steric substituent effects. This result is in agreement with the NEER principle. In addition, examples are given of changes in efficiency of light‐induced isomerizations, which are not restricted by the NEER principle. A reaction mechanism, involving a biradical intermediate, is proposed, which accounts for the formation of all of the reaction products containing a three‐membered ring. MO correlation diagrams show that the formation of the three‐membered ring as a primary step must occur in a conrotatory fashion.
1H NMR and 13C NMR spectroscopy of pyrene dianions
Authors: Rodenburg L. , Floor M. , Lefeber A. , Cornelisse J. , Lugtenburg J. 
Published: September 2010

AbstractA simple technique for the preparation of anions of polycyclic aromatic hydrocarbons is described. 1H and 13C NMR spectra of dianions of pyrene and derivatives of pyrene are reported and discussed. The electron density is greatest at the carbon atoms in the perimeter of the dianions. The presence of an electron‐donating substituent at position 2 causes an increase in the charge at positions 1 and 3.
An analysis of complex alkyl‐substituent effects in the water‐catalyzed hydrolysis of 1‐acyl‐1,2,4‐triazoles
Authors: Mooij Herman J. , Engberts Jan B. F. N. , Charton Marvin 
Published: September 2010

AbstractPseudo‐first‐order rate constants and thermodynamic activation parameters have been determined for the water‐catalyzed hydrolysis of the 1‐acyl‐1,2,4‐triazoles 1–9 in water and in aqueous acetonitrile [x(H2O) = 0.80]. The reaction occurs via water‐catalyzed nucleophilic attack of water at the amide carbonyl group. Variation of the alkyl group in the acyl part of the substrate led to the sequence of reactivities (in water): R = t‐Bu > i‐Pr > Et > Me > n‐Pr > s‐Bu > i‐Pent > neo‐Pent. This complex behavior strongly suggests the operation of a composite steric effect most likely involving contributions from conformational preference (SEI), change of coordination number at carbonyl carbon (SE2), steric repulsion between O2 and the alkyl group (SE3), and steric inhibition of solvation (SE4). Modelling of the relative rates in water in terms of the expanded branching equation gave satisfactory results. Two possible transition states are proposed for the neutral hydrolysis, one involving intramolecular hydrogen bonding between the second water molecule and N2 of the 1,2,4‐triazole ring. The different sequence of reactivities for neutral hydrolysis in aqueous acetonitrile as well as the rates for hydroxide‐ion‐catalyzed hydrolysis in water (B AC2 mechanism) support the analysis of substituent effects.
The electron spin resonance spectra of the radical cations of p‐terphenyl, triphenylene and triptycene
Authors: Courtneidge John L. , Davies Alwyn G. , Mcguchan Deborah C. 
Published: September 2010

AbstractThe ESR spectra of the radical cation of p‐terphenyl (1), triphenylene (2), and triptycene (3) have been investigated in fluid solution.
Reactions of (C5Me5)M(2,3‐dimethyl‐1,3‐butadiene)Cl (M = Ti, Hf) with symmetrical acetylenes
Authors: Hessen Bart , Teuben Jan H. 
Published: September 2010

AbstractThe reactivity of the electronically unsaturated diene complexes (C5Me5)M(2,3‐dimethyl‐1,3‐butadiene)Cl (M = Ti, Hf) with symmetrical acetylenes RCCR (R = H, Me, Ph) is reported. Whereas the reaction of the Hf complex with ethyne resulted in a product derived from initial insertion into the metal‐diene bond, elimination of the diene was observed in the other reactions. Two types of metallacyclo‐2,4‐pentadiene products, formed by oxidative coupling of acetylenes, were isolated: monomeric (C5Me5)Hf(C4Ph4)Cl and dimeric [(C5Me5)TiCl]2(C4Me4).
An experimental and theoretical study of the dimetallation of vinylacetylene
Authors: Brandsma Lambert , Hommes Hendrik , Verkruijsse Hermann D. , Kos Alexander J. , Neugebauer Wolfgang , Baumgärtner Wolfgang , von Ragué Schleyer Paul 
Published: September 2010

AbstractThe direct dimetallation of vinylacetylene (1‐buten‐3‐yne) at the 2‐ and 4‐positions can be achieved by the butyllithium‐potassiumtert‐butoxide reagent, but not when butyllithium is used alone or in the presence of TMEDA. Supporting experimental and calculational (ab initioand MNDO) results suggest that the potassium acetylide, KC≡C‐CH = CH2, is formed first. Further metallation occurs at the activated C‐2 vinyl position. Preferential substitution at the C‐2 position int‐BuC≡CCH = CHt‐Bu also was demonstrated. Neither dianion nor dilithium models account for the dimetallation results; in both cases, 1,4‐arrangements are indicated to be better than 2,4. The 2,4‐dimetallated vinylacetylene is a useful intermediate allowing the synthesis of derivatives inaccessible otherwise.
Alumina‐ and Y‐zeolite‐catalyzed reaction of cyclohexanol with tert‐butylhydroperoxide
Authors: Floor M. , Kieboom A. P. G. , van Bekkum H. 
Published: September 2010

AbstractThe use of γ‐alumina and exchanged Y‐zeolites as catalysts in the liquid‐phase oxidation of cyclohexanol by tert‐butyl hydroperoxide (tBHP) has been studied. With γ‐alumina, cyclohexanone is formed, whereas the zeolites NaCeY and NaLaY give cyclohexyl formate as the main product. This compound is thought to originate from a zeolite‐mediated rearrangement of tBHP to acetone and methanol, oxidation of methanol to formic acid and electrophilic addition of formic acid to cyclohexene (formed in situ from cyclohexanol).
Synthesis and structure of a bis‐ortho‐chelated aryllithium compound: 2,3,5,6‐tetrakis[(dimethylamino)methyl]phenyllithium dimer
Authors: van der Zeijden Adolphus A. H. , van Koten Gerard 
Published: September 2010

AbstractThe reaction of 1,2,4,5‐(Me2NCH2)4C6H2 with one equivalent of n‐butyllithium affords Li2[C6H(CH2NMe2)4‐2,3,5,6]2 (1). The molecule consists of a dimeric unit containing three‐centre, two‐electron lithium‐bonded aryl groups. The distorted tetrahedral coordination sphere of the lithium atoms is completed by two N‐coordinating ortho‐CH2NMe2 substituents. Complex 1 is the first dimeric aryllithium compound characterized in which the coordination around lithium is completed solely by intramolecular donating hetero atoms.
Studies in gas‐phase thermal hydrogenolysis. Part IV: Chlorobenzene and o‐dichlorobenzene
Authors: Manion Jeffrey A. , Dijks Johannes H. M. , Mulder Peter , Louw Robert 
Published: September 2010

AbstractThe gas‐phase thermolysis of chlorobenzene 1 and o‐dichlorobenzene 6 in H2 at atmospheric pressure between 773‐1280 K, τ = 3‐9 s, has been carried out in tubular and tank flow reactors. On a per‐chlorine basis, 1 and 6 react at almost identical rates; the major end products are HCl and benzene. Small amounts of biphenyl (3) and, at incomplete dechlorination levels, chlorobiphenyls are also formed.Dechlorination levels of 99.95% have been achieved. In an excess of H2, the pseudo‐first‐order rate constant for HCl production follows approximately log(k/s−1) ⋍ 10.9 ‐ 241.kJ/mol/(2.3. R. T) between 928 and 1155 K.The mechanism involves hydrogen atoms, which dechlorinate 1 and 6 via both ipso substitution and chlorine abstraction. At temperatures ≥ 900 K, atomic hydrogen is almost in equilibrium with H2, while at lower temperatures, production of H• can be chemically induced, leading to chain reactions and a steady‐state concentration of H• greater than that for equilibrium.
New base‐labile amino‐protective groups for peptide synthesis
Authors: Verhart C.G.J. , Tesser G.I. 
Published: September 2010

AbstractModification of the methyl group in 2‐(methylsulphonyl)ethanol gave alcohols which could be used to introduce amino‐protective groups of the urethane type, which are labile in alkaline media. The cleavage involves β‐elimination.Exchange of the methyl group by a phenyl group bearing a function with a negative inductive effect (NO2 or MeSO2) afforded protecting groups with a higher sensitivity to base. The recommended function is a disulphone: 2‐[4‐(methylsulphonyl)phenylsulphonyl]ethanol. The function has a somewhat better stability than the Fmoc group, resists catalytic hydrogenolysis, is highly stable in acidic medium and its elimination product does not polymerize spontaneously. The suggested designation of the new protective group is Mpc.
Conformational analysis of a biologically active heparin‐like compound, which contains an open chain fragment
Authors: van Boeckel C.A.A. , Wagenaars G.N. , Mellema J.‐R. 
Published: September 2010

AbstractConformational analysis of a biologically active heparin like oligosaccharide, which contains a glyceric acid‐O‐CH2‐O moiety instead of iduronic acid, was performed by high field (600 MHz) 1H‐NMR spectroscopy. Most remarkably, the glyceric acid ‐O‐CH2‐O moiety adopts a linear conformation in which the anomeric effect does not operate. Most likely, this phenomenon should be ascribed to electrostatic repulsions among the charged sulphate and carboxylate groups.
Acetalation studies. Part VII. Some new aspects of the isopropylidenation of galactitol
Authors: Chittenden Gordon J. F. 
Published: September 2010

AbstractReaction of galactitol in dimethyl sulphoxide, with 2,2,‐dimethoxypropane‐pyridinium p‐toluenesulphonate has led to the isolation of some new isopropylidene acetals. Their structures have been established spectroscopically. Attempts have been made to assess their possible role in the conventional acid‐catalysed isopropylidenation of this hexitol.
Hybridization of phosphate‐methylated DNA and natural oligonucleotides. Implications for protein‐induced DNA duplex destabilization
Authors: van Genderen Marcel H. P. , Koole Leo H. , Buck Henk M. 
Published: September 2010

AbstractDuplex stabilities have been determined for several hybrids of phosphate‐methylated oligonucleotides and natural DNA or RNA using UV hyperchromicity experiments. These hybrids have a higher stability than the corresponding natural duplexes, due to the absence of interstrand electrostatic repulsions. Comparison with stability data for hybrids of other neutral oligonucleotides (with phosphate‐ethylated and methyl phosphonate linkages) and natural DNA or RNA revealed that differences in stability could be attributed mainly to steric and stereoelectronic factors. For phosphate‐ethylated oligonucleotides, hybridization with a natural strand is strongly influenced by steric interactions of the ethyl group. Hybridization with RNA, which requires a tight A‐type conformation, is therefore difficult and the ethyl orientation (inward or outward, depending on the phosphorus configuration) determines the strength of the association with natural DNA. In methyl phosphonate systems, it appears that the presence of a PC bond disturbs the helix conformation for stereoelectronic reasons. This leads to a weaker hybridization with DNA and RNA for longer strands. Phosphate‐methylated oligonucleotides are found to have an optimal combination of steric and stereoelectronic factors and form the strongest hybrids with natural DNA. Absence of intrastrand phosphate‐phosphate repulsions causes a slightly different conformation for phosphate‐methylated DNA, which is evident in the cooperative character of the hybridization with natural DNA. A thermodynamic model for this cooperativity is presented and the model studies are extended to protein‐DNA complexes in which phosphate charges are also shielded. The preliminary results suggest that protein association can destabilize a DNA duplex, thus providing a possible mechanism for the action of DNA unwinding enzymes.
α‐Amino ketones derived from L‐proline, as precursors for isomitosanes and mitosenes
Authors: Orlemans E. O. M. , Verboom W. , Lammerink B. H. M. , Reinhoudt D. N. 
Published: September 2010

Abstract2‐Benzoyl‐ and 2‐(2‐naphthoyl)pyrrolidines which can be viewed as aryl α‐amino ketones, have been prepared from L‐proline via Grignard reactions, bromo‐to‐lithium exchange, or by Friedel‐Crafts acylations. It was impossible to convert the ketone function of these aryl α‐amino ketones into a tert‐alcohol group. The BOC‐protected (S)‐2‐acetyl‐l‐pyrrolidine (15), obtained by reaction of BOC‐proline 2‐pyridinethiol ester (2) with LiMe2Cu, could be converted in two steps into the amino alcohol 17, which contains a tert‐alcohol function. Upon treatment of 17 with BBr3, followed by air oxidation, mitosene 20 was obtained in a low yield. The Friedel‐Crafts reaction products 23 of 1,4‐dimethoxynaphthalene, or 2,5‐dimethoxytoluene and (S)‐l‐(trifluoroacetyl)–2‐pyrrolidinecarbonyl chloride, could be converted in two steps into the isomitosanes 25. The isomitosanes 25 could easily be dehydrated, using acid, to the corresponding mitosenes 26. Upon reduction of the isomitosanes 25 with Na2S,2O4 to the corresponding hydroquinones 28, spontaneous dehydration occurred.
The use of a double Wolff‐Kishner reduction in the preparation of aceanthrene and aceanthrylene
Authors: Boerrigter Jos C. Olde , Mulder Patrick P. J. , van der Gen Arne , Cornelisse Jan , Lugtenburg Johan , Mohn Georges R. 
Published: September 2010

AbstractAceanthrene (2) and aceanthrylene (1) are easily prepared in high yield from aceanthrenequinone (3) by means of a double Wolff‐Kishner reduction.
Reactions of 11C atoms with benzene. II. Formation of 11C‐labelled toluene and cycloheptatriene
Authors: Kuipers P. , van Halteren B. W. , Lindner L. , Brinkman G. A. 
Published: September 2010

AbstractThe reactions of recoil 11C atoms with liquid C6H6 result in the production of 11C‐labelled cycloheptatriene (CHT) and toluene in equal amounts of approximately 3%. From the effect of O2 on the product yields it is concluded that recoil labelling proceeds via both singlet and triplet 11CH2 intermediates, whereas 11CH may also contribute specifically to the formation of C6H5CH3. Addition of H2S increases the [11C]C6H5CH3 yield by ca. 5%, probably due to reactions of triplet phenyl‐carbene (C6H5CH). The reactions of singlet CH2, produced via the photolysis of CH2N2, with liquid C6H6 were also investigated in the presence of N2, O2 and I2.
Proton NMR study of alkali cation‐cyclogentiotetraose peracetate complexation
Authors: Bonas Georges , Vignon Michel 
Published: September 2010

AbstractComplexation studies of alkali cations with a cyclic tetrasaccharide made up of (1 → 6)‐β‐D‐gluco‐pyranosyl residues, cyclogentiotetraose peracetate (CGD4Ac) by proton n. m. r. spectroscopy in deuterated acetone and nitromethane are described.The ligand affinity decreases in both solvent, from cesium to lithium as follows: Cs+ ∼ Rb+ > K+ > Na+ > Li+, in agreement with the ligand cavity size (3.3 Å) calculated by molecular modelling.During complexation, a conformational change of the CGD4Ac ligand was observed, the gg conformer being predominent at the complexed state.
The “tert‐amino effect” in heterocyclic chemistry: Synthesis of tetra‐ and pentacyclic compounds
Authors: Nijhuis W. H. N. , Leus G. R. B. , Egberink R. J. M. , Verboom W. , Reinhoudt D. N. 
Published: September 2010

AbstractA new and convenient route for the synthesis of several heterotetra‐ and pentacyclic compounds is presented. Heating the 2‐vinyl‐N,N‐dialkylanilines 3a‐h, synthesized from the aldehydes 2a‐f,h or the acetophenone 2g and malononitrile or ethyl cyanoacetate, in refluxing 1‐butanol yields selectively the tetra‐ and pentacyclic compounds 4a‐h. This cyclization proceeds via a 1,5 hydrogen shift, followed by an addition of the carbanion to the iminium double bond. The benzo[f]thieno[3,2‐a]quinolizine 4c and the benzo[f]thieno[2,3‐a]quinolizine 4d represent new classes of heterocycles.The first example of formation of a six‐membered ring via carboncarbon bond formation, starting from 2‐vinyl‐substituted enamines, was the conversion of 5a and 5b into the benzo[h]pyrrolo[1,2‐a]‐quinoline 6a and the naphtho[2,1‐c]quinolizine 6b, respectively. Most probably, the cyclization of 5a and 5b proceeds in the same way as does the cyclization of the 2‐vinyl N,N‐disubstituted aniline derivatives.Heating the tricyano compound 5c in refluxing 1‐butanol gave both the benzo[g]pyrrolo[1,2‐a]indole 7 and malononitrile. This cyclization proceeds probably via a 1,6 hydrogen shift, followed by a 1,5 electrocyclization, and a subsequent fast elimination of malononitrile.
Synthesis of retinals labelled with 13C in the cyclohexene ring
Authors: Gebhard R. , Courtin J. M. L. , Shadid J. B. , van Haveren J. , van Haeringen C. J. , Lugtenburg J. 
Published: September 2010

AbstractIn this paper we report the synthesis of five retinals, specifically mono‐labelled with 13C at the positions 1, 2, 3 and 4 and di‐labelled with 13C at the positions 16 and 17, with more than 98% chemical purity and high 13C incorporation. (1‐13C)‐ and (16, 17‐13C2)retinal were obtained in 20% overall yield from (2‐13C)‐ and (1,3‐13C2)acetone. (2‐13C)‐ and (3‐13C)retinal were prepared in 10% overall yield from (1‐13C)‐ and (2‐13C)acetonitrile, while (4‐13C)retinal was synthesized in 17% overall yield starting from (2‐13C)acetonitrile.
Synthesis of fragments of the capsular polysaccharide of Haemophilus influenzae type b: Part IIII‐3. A solid‐phase synthesis of a spacer‐containing ribosylribitol phosphate hexamer
Authors: Elie C. J. J. , Muntendam H. J. , van den Elst H. , van der Marel G. A. , van Boom J. H. , Hoogerhout P. 
Published: September 2010

AbstractA solid‐phase synthesis of an aminohexyl‐containing hexameric fragment of the H. influenzae type b capsular polysaccharide, using a phosphoramidite approach and controlled‐pore glass as the solid support, is reported.
On the synthesis of bis{2‐(dimethylarsino)ethyl} amine
Authors: Edwards Peter G. , Wills A. Richard 
Published: September 2010

AbstractThe previously reported syntheses of HN(CH2CH2AsMe2)2 are found to be irreproducible. Two by‐products, the compound ClCH2CH2N(H)CH2CH2AsMe2 and the salt {H2N(CH2CH2AsMe2)2}+ I−, have been identified.
Sucrose‐derived dialdehydes: The course of the periodate oxidation as studied by HPLC
Authors: de Wit D. , van Rantwijk F. , Maat L. , Kieboom A. P. G. 
Published: September 2010

AbstractSucrose was oxidized with sodium periodate to di‐ and tetraaldehyde compounds. A fast and reliable analytical HPLC method was developed to follow the course of the reaction as a function of the amount of periodate added.Apart from the sucrose tetraaldehyde, i.e. the final oxidation product, only two out of the four possible sucrose dialdehyde products were formed: one with the glucose ring twice oxidized (GOO‐F) and one with an oxidized fructose ring (G‐FO). Both dialdehydes were formed in equal amounts when low amounts of periodate were added, whereas GOO‐F was preferentially formed when higher amounts of periodate were added.The course of the reaction is discussed in terms of internal hemiacetal formation of the sucrose dialdehydes.
Preparation and calcium complexation of oxidized polysaccharides. II: Hydrogen peroxide as co‐reactant in the chlorite oxidation of dialdehyde glucans
Authors: Floor M. , Hofsteede L. P. M. , Kieboom A. P. G. , van Bekkum H. , Greenland W. P. T. , Verhaar L. A. Th. 
Published: September 2010

AbstractA series of dialdehyde glucans (obtained from starch, cellulose and dextran by periodate glycol cleavage) were oxidized to the corresponding dicarboxy polysaccharides by the combined use of sodium chlorite and hydrogen peroxide (two moles of each per mole dialdehyde moieties). As compared to the conventional method (using six moles of chlorite), this new procedure (i) reduces oxidant costs by a factor of 2.5, (ii) avoids the evolution of toxic chlorine dioxide and (iii) more selectively yields dicarboxy polysaccharides of high molecular weight with excellent calcium complexing properties. The products thus obtained are potentially attractive co‐builders in phosphate‐free detergents.