bluuebunny/crossref_metadata_2025 huggingface dataset:
Cannabis XIX. Oxygenated 1,2‐Diphenylethanes from Marihuana
Authors: Kettenes‐van den Bosch J. J. , Salemink C. A.
Published: September 2010

The presence of several hydroxy‐ and methoxy‐substituted 1,2‐diphenylethanes in Mexican marihuana has been established. The structure of three of these compounds has been elucidated. The products may have physiological activity. Their role as precursors for cannabispiro compounds is discussed.
On the reversibility of the formation of peroxyl radicals from oxygen and alkyl radicals
Authors: Bolsman T. A. B. M. , Brouwer D. M.
Published: September 2010

Generation of the 16O‐tert‐butylperoxyl radical at 130°C in the presence of 18O2 does not result in the incorporation of 18O into the decomposition products, which confirms that the dissociation of the peroxyl radical into molecular oxygen and an alkyl radical is very slow compared with the propagation step in the autoxidation of isoalkanes.
The role of tetraalkylammonium salts in the electro‐reduction of ketones. I. Competitive adsorption in an aqueous medium
Authors: van Tilborg W. J. M. , Dekker L. J. G. , Smit C. J.
Published: September 2010

Aryl alkyl ketones and tetraalkylammonium ions compete for adsorption in the region where the adsorption voltage ranges of the respective compounds overlap. A study has been made of the effects of changes in structure of the tetraalkylammonium salts as well as of the ketones, of the nature of the anion and of the polarity of the medium on this competitive adsorption. It is concluded that in the presence of tetraalkylammonium ions the reduction of a corbonyl compound occurs on top of an adsorbate layer of such ammonium ions. Consequences of the results reported with respect to the mechanism of asymmetric induction in carbonyl reduction and of the mechanism of electropinacolization are discussed.
X‐Ray structure of the inherently dissymmetric olefin D,L‐trans‐1,2,3,4,1′,2′,3′,4′‐octahydro‐4,4′‐biphenanthrylidene
Authors: Feringa Ben , Wynberg Hans , Duisenberg Albert J. M. , Spek Anthony L.
Published: September 2010

X‐Ray data for inherently dissymmetric D,L‐trans‐1,2,3,4,1′,2′,3′,4′‐octahydro‐4,4′‐biphenanthrylidene are presented; the molecular symmetry is C2. Small double‐bond torsion and twist boat cyclohexene conformations have been established.
The molecular structure of 3β‐acetoxy‐2β‐hydroxy‐thujopsane, C17H28O3
Authors: Olthof G. J. , Overbeek A. R. , Putten N. V. D. , Schenk H.
Published: September 2010

The sesquiterpenoid 3β‐acetoxy‐2β‐hydroxy‐thujopsane forms orthorhombic crystals of space group P212121 with cell dimensions a = 7.547, b = 14.167, c = 14.783 Å and Z = 4. The cyclohexane ring carrying the cyclopropane ring is approximately in a half chair conformation and the other ring is a slightly deformed chair. Two bonds of the cyclopropane ring are shortened (to 1.490 and 1.492 Å) and one is lengthened (to 1.534 Å), an uncommon phenomenon, which is assumed to be correlated with the position of the hydroxyl‐oxygen atom with respect to the cyclopropane ring.
Propellanes. XLVII. The reaction of 11,13‐dioxo‐12‐methyl‐12‐aza[4.4.3] propella‐2,4,7,9‐tetraene and ‐2,4‐diene with singlet oxygen
Authors: Landheer Iman , Ginsburg David
Published: September 2010

Singlet oxygen attacks 3 from the direction syn to the hetero‐ring.
Photochemistry of vicinal diaryl tetraketones
Authors: Rubin Mordecai B. , Krochmal Emil C. , Kaftory Menahem
Published: September 2010

Irradiation of vicinal diaryl tetraketones in a variety of solvents yields tricyclic products 2 in high yields. The structure of the product from di‐p‐bromophenyl tetraketone was determined by X‐ray crystallographic analysis.
1H‐CIDNP effects in the reaction of N‐hydroxyureas with tert‐butylsulfinyl chloride in the presence of a tertiary amine
Authors: Bleeker Ido P. , Engberts Jan B. F. N.
Published: September 2010

tert‐Butylsulfinyl chloride (1) reacts smoothly with N′‐(di)methyl‐ and N′‐(di)phenyl‐N‐hydroxyurea (2) in acetone at room temperature, in the presence of two equivalents of pyridine. An intermediate O‐tert‐butylsulfinyl‐N‐hydroxyurea (3) is postulated, which rearranges via a radical cage mechanism to give the corresponding N‐tert‐butylsulfonylurea as the recombination product. Several escape products are also isolated. This thermally induced rearrangement involves homolytic cleavage of the N‐O bond in 3. The process is accompanied by pronounced 1H‐CIDNP effects, which may be interpreted using Kaptein's rule. The fate of the N′‐(di)substituted carbamoylaminyl radicals, formed initially within the radical pair, is discussed. N′,N′‐diphenyl‐N‐hydroxyurea shows deviant behaviour and the major reaction product is in this case diphenylamine.
Geometrical isomers of thione S‐imides
Authors: Tangerman A. , Zwanenburg B.
Published: September 2010

Reaction of highly substituted dithiobenzoates 1 (a‐e) with chloramine‐T in methanol at 20°C gives, in high yields, thione S‐imides 2 (a‐e) to which the E‐geometry was assigned. Heating of these compounds in methanol for 1 hr causes thermodynamic isomerization to the Z‐isomers 3 (a‐e). Similarly, 2,4,6‐trimethyl‐thiobenzophenone gives the corresponding E‐ and Z‐S‐tosylimides 6 and 7. Irradiation of thione S‐imides 2, 3, 6 and 7 leads to extrusion of sulfur yielding N‐tosylimines 4 and 8. The geometrical configurations were based on ASIS experiments. From the 1H‐NMR spectra of 2 and 3 the preferred conformation of the thione S‐imides have been deduced (S‐trans conformation for the E‐isomer 2 and a folded S‐cis conformation for the Z‐isomer 3). It will be shown that in order to obtain stable thione S‐tosylimides from dithiobenzoates and thiobenzophenones, steric hindrance in the direct environment of the thiono function is a prerequisite.
Photochemical cycloaddition of an aromatic ketone to a 1‐alkynyl ether. Kinetics and mechanism
Authors: Polman H. , Baaij J.P.B. , Bos H.J.T.
Published: September 2010

In this paper kinetics and mechanism of the photoaddition of 10,11‐dihydro‐5H‐dibenzo‐[a,d]cyclohepten‐5‐one (dibenzosuberone, 4) to 1‐methoxy‐1‐propyne (5) with the formation of the unsaturated ester 8, are studied. In benzene at 25.0°C a limiting quantum yield Φ = 0.04 was found. The rate constant k2 of the addition of triplet ketone 4 to ground state 5 amounted to 1.9 · 1077 l.mol−1,s−1. The unexpected regiospecificity is not caused by attack of triplet alkyne on ground state ketone. The low quantum yield is mainly caused by the high revertibility of the addition reaction. The intermediacy of a triplet exciplex is discussed.
A study on the regio‐ and stereo‐chemistry of organocuprate additions to 1,2,3‐butatrienes
Authors: Kleijn H. , Westmijze H. , Schaap A. , Bos H.J.T. , Vermeer P.
Published: September 2010

A number of 1,2,3‐butatrienes, R1R2CCCCH2 (1; R1 = H, Me or t‐Bu; R2 = H or Me) have been allowed to react with organocuprates of the type R32CuMgX·LiBr (2; R3 = alkyl or Ph) in tetrahydrofuran. In most cases the (E)‐1,3‐dienes R1R2CCHCR3CH2 (3) are formed mainly but sometimes substantial amounts of the compounds R1R2CCCHCH2R3 (4), R1R2CHC≡CCH2R3 (5) and R1R2CCR3‐CHCH2 (6) have also been isolated. A mechanism for the addition reaction is proposed.
Biomimetic total synthesis of steroids IV. Stereoselective synthesis of 15α‐methyl‐19‐norsteroids
Authors: Groen M.B. , Zeelen F.J.
Published: September 2010

The cationic cyclization of 2‐[6‐(m‐methoxyphenyl)‐(E)‐3‐hexenyl]‐3,5‐dimethyl‐2‐cyclopentenol (3) was investigated. Exclusive formation of 1‐ and 3‐methoxy‐15α,17‐dimethyl‐1,3,5(10), 13(17)‐gonatetraene (4 and 5) was observed, indicating complete stereoselectivity in the cyclization process. Compound 4 was converted into dl‐15α‐methylestrone methyl ether (7) and hence into dl‐15α‐methylestradiol 3‐methyl ether (8). The structure of these hitherto unknown compounds was proved by independent syntheses.
Chiral organolead compounds. Part 1. [2‐(Dimethylaminomethyl)phenyl](4‐methoxyphenyl)(4‐methylphenyl) lead iodide
Authors: van der Kooi H. O. , Wolters J. , van der Gen A.
Published: September 2010

A synthetic route to a chiral triorganolead halide of the type ArAr′Ar″PbX is described. A prochiral diorganolead diacetate was prepared by plumbylation and subsequent transmetallation. After substitution of the two acetate groups by iodide, the prochiral intermediate was selectively arylated with ortho‐lithiated N,N‐dimethylbenzylamine in which a potential built‐in ligand is present. The PMR spectrum of the resulting chiral triorganolead iodide showed no diastereotopic effects of the N(CH3)2 and of the benzylic protons. Data of the crystal and molecular structures of this novel chiral lead compound obtained from a single‐crystal X‐ray diffraction study are reported. The crystal structure is isomorphous with that of [2‐(dimethylaminomethyl)phenyl]diphenyltin bromide.
The effect of γ‐substituents on the vicinal carbon‐proton spin‐spin coupling constants in aliphatic compounds
Authors: Spoormaker Tom , Zwikker Jan W. , de Bie Marius J. A.
Published: September 2010

The increments in 3J(CH) for substituents attached to Cγ in the 13Cα‐Cβ‐Cγ‐1H coupling pathway, with respect to 3J(CH) in propane are calculated for equal Cβ‐Cγ rotamer population from 3J(CH) observed in the corresponding neopentyl compounds. From these increments the preferred conformation of the n‐propyl compounds can be deduced.
Réactions d'oximation de cétones III. Effets de structure dans la réaction d'addition neutre et acido‐catalysée de l'hydroxylamine
Authors: Lamaty G. , Petitjean A. , Roque J. P. , Natat A.
Published: September 2010

Rate constants for addition of hydroxylamine to a series of twenty‐four ketones have been measured, in water at 25,00 ± 0,02°C, for both acid‐catalyzed (k) and pH‐independent (ko) pathways. Structural effects seem to be operating in the same manner on ko and k values, except in a few cases. Results are consistent with a “reactant‐like” transition state.
Zinc(II), cadmium(II) and mercury(II) complexes with 2,5‐diphenyloxazole
Authors: Biddau M. , Massacesi M. , Pinna R. , Ponticelli G.
Published: September 2010

A number of compounds of general formula M(PPO)nX2 are described, the metal ion being Zn(II), Cd(II) and Hg(II) and the anions Cl−, Br−, I−, NO3−, ClO4− and NCS−; PPO stands for 2,5‐diphenyloxazole and n = 1, 2, 4.

The complexes are prepared by reaction of the corresponding metal salts with the molten ligand in the required stoicheiometrical ratio and are characterized by chemical analyses and physical measurements.

Their stereochemistry has been assigned on the basis of IR, far IR spectroscopy and molar conductivity values. The ligand PPO is shown to co‐ordinate with metal ions via the lone‐pair electrons of the nitrogen atom. All the complexes have generally a distorted tetrahedral stereochemistry.
Reactions d'insertion du phénylphosphinidène dans diverses liaisons germanium‐hétéroélément
Authors: Escudié J. , Couret C. , Satgé J.
Published: September 2010

Phenylphosphinidene inserts into Ge‐Y bonds (Y = H, C, N, O, P) with formation of germylphosphines with a magnified image structure. However some adducts (Y = N, O, P) undergo a thermal redistribution reaction giving particularly bis(trialkylgermyl)phosphines. Insertion reactions of phenylphosphinidene into Si‐P or Ge‐P bonds of 2‐sila or 2‐germaphospholanes lead to a new class of cyclic metalla‐IVb‐diphosphines, the 3‐sila‐ or 3‐germa‐1,2‐diphosphorinanes.
Synthesis of (E,E)‐1,5‐cyclodienes. Part II
Authors: Reijnders Peter J. M. , Fransen Harrie R. , Buck Henk M.
Published: September 2010

The synthesis of (E,E)‐1,5‐cyclodienes is described. The preparation of these ring systems is accomplished by intramolecular coupling of (E,E)‐3,3′‐polymethylenebis(allyl bromides), with bis(1,5‐cyclooctadiene)nickel(0). In this way the fourteen, sixteen and eighteen ring can be prepared in good yield. Synthesis of the twelve ring in this manner fails and gives only cyclodimers and acyclic products.

Synthesis of (E,E)‐1,5‐cyclododecadiene is accomplished by reduction of (E,E,E)‐1,5,9‐cyclododecatriene.
Synthesis of complementary DNA fragments via phosphotriester intermediates
Authors: de Rooij J. F. M. , Wille‐Hazeleger G. , van Deursen P. H. , Serdijn J. , van Boom J. H.
Published: September 2010

The preparation of the complementary oligodeoxyribonucleotides Ia,b and II via a modified phosphotriester method is described. The synthesis of these compounds was accomplished by using: (a) the levulinyl group for temporary and persistent blocking of the 5′‐hydroxyl; (b) the monofunctional phosphorylating agent 2,2,2‐trichloroethyl 2‐chlorophenyl phosphorochloridate (3) to introduce the phosphate moiety at the 3′‐position; (c) the benzoyl group to protect the terminal 3′‐hydroxyl; (d) acyl groups for the protection of the exocyclic amino functions of the bases; and (e) 1‐(2,4,6‐triisopropylbenzenesulphonyl)‐3‐nitro‐1,2,4‐triazole (TPS‐NT, 11c) as activating agent in the formation of phosphotriester linkages. Final removal of all protecting groups was performed by fluoride ion treatment followed by aqueous ammonia. The oligonucleotides Ia,b and II were, after purification, isolated in good yields and, as followed from HPLC analysis, in high purity.
The use of trifluoroacetic acid in the reverse‐phase liquid chromatography of peptides including secretin
Authors: Voskamp D. , Olieman C. , Beyerman H. C.
Published: September 2010

The reverse‐phase high‐performance liquid chromatography of underivatized peptides has been studied. The addition of trifluoroacetic acid — lipophilic ion‐pairing reagent — to the mobile phase gave excellent conditions for the analytical and preparative separation on octadecylsilyl‐silica of peptides varying in size from a 2‐peptide to a 32‐peptide (human calcitonin) inclusive.

The gastrointestinal 27‐peptide hormone secretin could thus be purified on a preparative scale and intramolecular rearrangements in hexapeptide fragments of secretin could be monitored in this way.
Synthesis of porcine motilin via its sulfoxides
Authors: Izeboud E. , Beyerman H. C.
Published: September 2010

The protected segments corresponding to sequences 1‐8 and 9‐22 proposed for porcine motilin were synthesized mainly by the repetitive excess mixed anhydride (REMA) method. Mixed anhydride coupling of the segments gave protected motilin sulfoxide (Scheme). Deprotection with liquid hydrogen fluoride yielded the crude motilin sulfoxides which, after purification by HPLC on a semi‐preparative scale, were quantitatively reduced by iodide in aqueous trifluoroacetic acid.

According to Dr. Zen Itoh, Japan, the minimum dose of our REMA‐synthesized motilin required to induce interdigestive migrating contractions (IMC) in dogs was 0.03 μg/kg.h, which indicates a potency of about ten times the standard synthetic preparation used in the assay. In a comparison with natural porcine motilin by Dr. Pierre Poitras, U.S.A., REMA‐motilin showed at least 100% immunological cross‐reactivity.
Mechanism of action of coenzyme B12. Quantum‐chemical considerations
Authors: Merkelbach Ingrid I. , Buck Henk M.
Published: September 2010

Quantum‐chemical calculations are carried out on simplified models to obtain insight in the mechanistic aspects of coenzyme B12
Direct proof for the occurrence of anions in the base‐induced 1,4‐elimination of alcohol from 1,4‐dialkoxy‐2‐butynes
Authors: van Rijn P. E. , Everhardus R. H. , Brandsma L.
Published: September 2010

1,4‐Elimination of alcohols from ether of the type RO‐CH2 ‐C≡C‐CH2‐OR by treating these compounds with alkali amide, appears to be not a concerted process, but to proceed via short‐lived anions. These anions can be intercepted by ethyl bromide, present during the reaction.
A model description for the initiation of conformational changes in DNA via the P(IV) residues. Part I
Authors: Buck Henk
Published: September 2010

A mechanistic model is presented for the conversion of right‐handed DNA into left‐handed DNA. In this model the co‐ordination of phosphorus plays a key role.
Electrosynthesis of cyclopropanone adducts
Authors: van Tilborg W. J. M. , Plomp R. , de Ruiter R. , Smit C. J.
Published: September 2010

Electroreduction of α,α′‐dihalo ketones to cyclopropanones (isolated as the hemiacetals or hemiacylals) is accomplished with good yields only with highly alkylated α,α′‐dihalo ketones. Attempts to prepare little substituted or unsubstituted cyclopropanone (derivatives) by electroreduction of α,α′‐dihalo ketones in which the carbonyl group is protected as an acylal or aminal resulted in the isolation of the desired compounds in low yields. The cyclisation reaction cannot compete successfully with side‐reactions. With acetals as the protecting group, the reductive cyclisation proceeds smoothly. Contrary to the acetals, the cyclopropanone acylals are excellent precursors for cyclopropanone.
Kinetic studies on the nucleation and growth of silicon via chemical vapour deposition
Authors: Bloem J. , Claassen W. A. Y.
Published: September 2010

Chemical vapour deposition (CVD) of silicon on various substrates is a well‐known technique in semiconductor technology.

An experimental study has been made of the nucleation of silicon on SiO2, and Si3N4, substrates together with a search for rate‐limiting steps in the growth of silicon from silane (SiH4) and chlorosilanes.

Analysis of the experimental data shows that the nucleation depends on the concentration of silicon adatoms on the surface, (Si*). After formation of stable nuclei and coalescence of the growing domains, further growth of silicon on silicon proceeds.

For the growth of silicon via silane the rate‐limiting reaction could not be indicated exactly; addition of some HCl results in a rapid change of the surface species into SiCl2*, indicating that the rate‐limiting step has to be found at the end of the chain of surface reactions. This conclusion is confirmed by experiments with an input of SiH2Cl2, in which case the SiCl2* surface species predominates. Reduction to silicon is then found to be the rate‐limiting reaction. The reduction or desorption of chlorine probably takes place at specific sites on the surface, such as atomic surface steps where an adsorbed SiCl2, molecule can form a second silicon‐silicon bond.

The adsorption of monoatomic hydrogen and chlorine on the silicon surface has been analysed and the conclusion is drawn that these surface species are not present in a sufficient concentration to turn the initial adsorption or the surface diffusion of silicon‐containing compounds into rate‐limiting reactions.
Enamine reactivity of 3‐(l‐pyrrolidinyl)heteroaromatics: Reactions with ketenes and nitro‐olefines
Authors: Mutreja H. C. , Reinhoudt D. N.
Published: September 2010

Ketenes react with 1‐pyrrolidinyl‐substituted heteroaromatics 3‐5 to give 2‐acyl derivatives 10, 13, 16‐18 and 20 and, in some cases 2: 1 reaction products 11 and 12. The latter products can be attributed to reaction of 1,4‐dipolar intermediates with a second molecule of ketene. With β‐nitro‐styrene, compounds 4b and 5 give only the corresponding 2‐alkyl‐substituted products 21 and 22, respectively. These reactions further demonstrate the “enamine‐like” character of 3‐(1 ‐pyrrolidinyl)‐substituted heteroaromatics 3‐5.
An approach to 11β‐isopropoxymethyl steroids
Authors: Loozen H. J. J. , de Winter M. S.
Published: September 2010

A route for the preparation of 11β‐isopropoxymethyl derivatives of steroids is exemplified by the preparation of (11β, 17α)‐17‐hydroxy‐11‐(isopropoxymethyl)‐19‐norpregn‐4‐en‐20‐yn‐3‐one (1). To this end (11β)‐11‐(hydroxymethyl)‐3‐methoxyestra‐1,3,5( 10)‐trien‐17‐one cyclic ethylene acetal (2) was converted into its 11β‐(2‐hydroxyethoxy)methyl derivative 5. Oxidation of 5 to the corresponding 11β‐(carboxymethoxy)methyl derivative 7, followed by methylation and subsequent reduction gave (11β)‐3‐methoxy‐11‐[(1‐methylethoxy)methyl]estra‐,3,5(10)‐trien‐17‐one cyclic ethylene acetal (13). Birch reduction and ethinylation provided 1.
Zinc(II)‐promoted reduction of ketones by 1‐methyl‐1,4‐dihydropyridines
Authors: de Koning A. J. , Alberts‐Jansen H. J. , Boersma J. , van der Kerk G. J. M.
Published: September 2010

Zinc(II) promotes the reduction of unactivated ketones and aldehydes by (methyl‐substituted) 1‐methyl‐1,4‐dihydropyridines. Coordination of the dihydropyridines to the metal, which occurs via their annular nitrogen atoms, is essential for hydrogen‐transfer. The reductions proceed best in apolar non‐aromatic solvents, which are unable to compete with the carbonyl group of the substrate for a coordination site at the metal. Virtually no hydrogen‐transfer takes place in the absence of Zn(II) salts or when zinc coordination complexes are used in which the metal is coordinatively saturated.

The results of this study are discussed in terms of a possible relationship with the role of zinc in alcohol dehydrogenases and metal‐catalyzed reductions in biomimetic systems.
Reductive elimination and skeletal rearrangement of β‐hydroxy selenide derivatives of bicyclo[4.2.l]nonatriene in a super acid medium
Authors: Gillissen Huub M. J. , Schipper Pieter , Buck Henk M.
Published: September 2010

In sulfur dioxide the β‐hydroxy selenides 1 and 2 produce rearranged selenides 6 and 7 upon addition of fluorosulfonic acid. Reductive elimination and subsequent attack of the selenenyl electrophile on the etheno bridge cause migration of the butadiene moiety.
Salt‐induced conversions of P(V) into P(IV) in solvents of different polarity. A tentative model for the initiation of conformational changes in DNA via the P(IV) residues
Authors: Castelijns Marianne M. C. F. , van Aken Dirk , Schipper Pieter , van Lier Johan J. C. , Buck Henk M.
Published: September 2010

Evidence is presented for the involvement of pentaco‐ordinated phosphorus intermediates in the rate‐determining step of the de‐alkylation reactions of some phosphates and phosphonates with LiCl and LiBr. Such involvement is suggested to lead to the zwitterionic pentaco‐ordinated phosphorus complexes 5a and 5b, respectively when compounds 2a and 2b are treated with LiCl and LiBr. The existence of these complexes shows unambiguously the possibility of inducing (slight) conformational changes of phosphorus in the presence of cations and anions (or nucleophilic solvents). This approach may also be useful for the description of conformational changes in phosphate residues in DNA, thus leading to different conformations of DNA.
Complexes of nickel(II) and copper(II) halides, nitrates and thiocyanate with racemic 1‐amino‐2‐propanol as a ligand
Authors: Nieuwpoort G. , Groeneveld W. L.
Published: September 2010

The preparation of complexes containing Ni(II) and Cu(II) as metal ions, racemic 1‐amino‐2‐propanol as ligand together with halides, nitrate and thiocyanate as anions, is described. Infrared and ligand field spectra have been used to obtain information about the coordination of the ligand. X‐Ray powder diffractograms of the complexes have been recorded. Conclusions about the structure of the complexes are drawn.
A study of lanthanide(III) (hydroxy)carboxylate complexes in aqueous medium using lanthanide induced oxygen‐17 NMR shifts
Authors: Vijverberg C. A. M. , Peters J. A. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

The complexation of dysprosium(III), as the model cation for calcium(II), with a series of (hydroxy)carboxylates in aqueous medium, has been studied by 17O NMR spectroscopy. Acetate, 3‐hydroxybutyrate, glycolate, lactate, malonate, malate and citrate show fast ligand exchange on the 17O NMR time scale at 73°. The Dy(III)‐induced 17O shifts of both the ligand and the water, which are mainly due to contact interaction, provide valuable information on the complexation sites of the ligands as well as on the number of coordinated waters in the complexes. The results point to a rather constant 17O contact shift upon the formation of Dy(III)‐O bonds.

On the other hand, oxydiacetate (ODA), (carboxymethoxy)succinate (CMOS) and nitrilotriacetate (NTA) show slow ligand exchange on the 17O NMR time scale at 73°. In these cases the Dy(III)‐induced shift of the 17O water resonance provides information on the stoichiometry of the complexes, i.e. the number of coordinated waters and the number of ligands.
A convenient synthesis of 1,3‐dithioles, 1,3‐thiaselenoles and 1,3‐thiatelluroles
Authors: Sukhai R. S. , Verboom W. , Meijer J. , Schoufs M. J. M. , Brandsma L.
Published: September 2010

Reaction of 1‐(chloromethylthio)‐1‐alkynes (RCCSCH2Cl, R  alkyl or phenyl) with an alkali metal sulfide, selenide or telluride gives 4‐substituted 1,3‐dithioles together with the corresponding 1,3‐thiaselenoles and 1,3‐thiatelluroles in good yields. The compounds RCCSCH2Cl can be obtained either from lithium alkynethiolates (RCCSLi) and BrCH2Cl or from alkynyllithium (RCCLi) and chloromethyl thiocyanates (ClCH2SCN).
Studies on polypeptides XXXIV. Replacement of histidine‐2 in Luliberin (LH‐RH) by L‐homohistidine
Authors: Raap J. , Kerling K. E. T.
Published: September 2010

[Homohistidine2]LH‐RH has been synthesized by the solid phase method. NMR and CD spectra at two pH values have been measured. The remarkably low in vitro potency of the component, relative to LH‐RH, is discussed in terms of conformational differences.
Synthesis and melanotropic activity of γ‐melanotropin
Authors: Bijl W. A. A. J. , van Nispen J. W. , Greven H. M.
Published: September 2010

γ‐MSH, a third melanotropic sequence in the N‐terminal cryptic portion of the ACTH/β‐LPH precursor molecule pro‐opiocortin, was synthesized by the fragment condensation approach. The dodecapeptide H‐Tyr‐Val‐Met‐Gly‐His‐Phe‐Arg‐Trp‐Asp‐Arg‐Phe‐Gly‐OH was tested for melanocyte‐stimulating activity on the skin of the lizard Anolis Carolinensis and was found to possess only 2.5 × 10−4 of the activity of α‐MSH.
Cycloaddition reactions of cyclooctyne with 9,10‐phenanthrenequinone and 3,5‐di‐tert‐butyl‐o‐benzoquinone
Authors: Verboom W. , Bos H. J. T.
Published: September 2010

Treatment of a solution of 9,10‐phenanthrenequinone 4 and cyclooctyne 2 in chloroform with boron trifluoride‐ether affords the quinoid α,β‐unsaturated ketone 5 with loss of carbon monoxide. Reaction of 3,5‐di‐tert‐butyl‐o‐benzoquinone 9 with cyclooctyne 2 gives rise to formation of the Diels‐Alder adduct 10 and a bridged cycloheptadienone derivative 11; under the influence of boron trifluoride‐ether, however, the reaction leads, in addition to 11, to formation of the isomeric cycloheptadienone derivative 12, while the Diels‐Alder adduct 10 is converted into the cycloheptadienone derivative 11.
Activity and enantioselectivity in the hydrolysis of substituted phenyl esters catalysed by imidazole‐containing poly(iminomethylenes)
Authors: van der Eijk J. M. , Nolte R. J. M. , Richters V. E. M. , Drenth W.
Published: September 2010

The hydrolysis of achiral and chiral esters by optically active poly(iminomethylenes), [R‐NC<]n, which contain imidazole groups in their side chains R, has been studied. The polymers include poly(L‐ and D‐carbylalanyl‐L‐histidine), 2d and 2e, poly(D‐carbylalanyl‐L‐histidinol), 2f, and poly(L‐carbyl‐α‐methylhistamine), 1c. The esterolytic catalytic activity of the polymers towards neutral and charged esters increases in the series 2d, 2e >> 1c < 2f. Poly(D‐carbylalanyl‐L–histidinol) shows enantioselectivity in the hydrolysis of p‐nitrophenyl esters of D‐ and L‐amino acids, kL/kD = 1.1.
Thioureido complexes of copper(I), copper(II) and copper(III). Crystal structure of the copper(I) complex [Cu[(C6H5)NC(S)N[(C2H4)2O]]]6
Authors: Willemse J. , Bosnian W. P. , Noordik J. H. , Cras J. A.
Published: September 2010

Deprotonated N‐phenyl,N′,N′‐dialkylthiourea (PhtuR2) complexes of Cu(I) and Cu(II) have been isolated and the existence of a Cu(III) complex inferred from electrochemical measurements. The crystal structure of Cu(I)[(C6H5)NC(S)N[(C2H4)2O]] (space group Pl̄, Z = 24, a = 10.487(9), b = 28.961(8), c = 29.579(12) Å, α = 120.72(3), β = 103.69(5), γ = 83.14(4)°) revealed 4 hexameric units per unit cell. The metals form a distorted octahedron; the ligands are situated outside six of the faces of this octahedron. The copper coordination is threefold planar; a N atom is linked to one Cu and the S atoms to two Cu atoms. The Cu–Cu distances exclude strong metal‐metal interactions. ESR measurements on Cu(II)(PhtuBu2)2 suggest a planar coordination around Cu with the N atoms in trans‐position. Cyclic voltamograms and differential pulse polarograms show the one‐electron oxidation, Cu(II)(PhtuR2)2 → Cu(III)(PhtuR2)2 + + e. The Cu(III) complex is only stable on the electrochemical time scale (scan rate 100 mV s−1).
Preparation of 6‐demethoxythebaine from neopine and its Diels‐Alder reaction with ethyl acrylate (Chemistry of opium alkaloids, Part XV)
Authors: Crabbendam P. R. , Maat L. , Beyerman H. C.
Published: September 2010

6α‐O‐Methanesulfonylneopine (3b) was converted into 6‐demethoxythebaine (4b) with the aid of potassium tert‐butoxide. Diels‐Alder reaction of 6‐demethoxythebaine with ethyl acrylate yielded mainly 4,5‐epoxy‐6,14‐endo‐etheno‐7α‐ethoxycarbonyl‐3‐methoxy‐17‐methylmorphinan (5b), an intermediate for the synthesis of potential analgesics.
The reactivity of the cyclic systems (NPCl2)3−n(NSOX)n (n = 0,1; X = Cl, Ph) towards aziridine
Authors: van der Huizen A. A. , Jekel A. P. , Rusch J. , van de Grampel J. C.
Published: September 2010

The aziridinolysis of (NPCl2)3 and (NPCl2)2NSOCl proceeds both via a geminal and non‐geminal pattern, whereas (NPCl2)2 NSOPh reacts almost exclusively via a geminal pathway. The presence of a P‐amino group (pyrrolidino, piperidino or morpholino) reduces the reactivity of the phosphorus centre concerned.
Mössbauer investigation of gold cluster compounds
Authors: Vollenbroek F. A. , van der Velden J. W. A. , Bour J. J. , Trooster J. M.
Published: September 2010

The Mössbauer spectra of Au11L7X3, [Au11 L8X2]PF6, [Au11(dppp)5](SCN)3, [Au8L8](PF6)2 and [Au9L8](PF6)3 (L = PPh3, X = SCN, Cl or CN, dppp = 1,3‐bis(diphenyl‐phosphino)propane) are presented and interpreted on the basis of three different gold sites, namely: (1) a central gold atom, (2) peripheral gold atoms coordinated to phosphines and (3) peripheral gold atoms coordinated to (pseudo)halides. The peripheral gold atoms in all the clusters behave like linearly hybridized atoms. The zero quadrupole splitting of the central gold atom reflects the almost spherical environment of this atom in the clusters, with [Au9L8]3+ being a remarkable exception.
Synthesis, structure and magnetism of di‐μ2‐fluorobis(3,5‐dimethylpyrazole)tetrakis(5‐methylpyrazole)dicopper(II) bis(tetrafluoroborate)
Authors: ten Hoedt R. W. M. , Reedijk J. , Verschoor G. C.
Published: September 2010

The molecular structure of the compound Cu2F2(DMPZ)2(MPZ)4(BF4)2 (DPZ = 3,5‐dimethylpyrazole; MPZ = 5‐methylpyrazole), determined by single‐crystal X‐ray analysis, is described. The compound was obtained via partial substitution of DMPZ ligands in Cu2F2‐(DMPZ)6(BF4)2.

The compound crystallizes in space group P1, with a = 9.578(2) Å, b = 9.893(1) Å, c = 10.994(2) Å, α = 104.27(1)°, β = 109.04(2)°, γ = 99.12(1)° and Z = 1. Reflection data were collected using an Enraf‐Nonius CAD‐4 single‐crystal diffractometer and graphite‐monochromated Mo‐Kα radiation. The structure was solved using conventional Patterson, Fourier and least‐squares refinement techniques. The final conventional discrepancy index (R) was 4.1%, based on 4442 independent reflections.

The compound is dimeric, having asymmetric fluoro bridges (CuF: 1.904(2) and 2.258(2) Å) with a CuFCu angle of 97.19(8)° and a Cu–Cu distance of 3.131(1) Å. The copper atom is in a square‐based pyramidal coordination geometry with one fluoride ion in apical position. Strong HF interactions were observed between the NH protons of the substituted pyrazole ligands and the bridging fluoride ion as well as with one or two of the fluorides of the BF4− anion. The BF4− anion is present in two different orientations having one BF bond in common, i.e. they are related by a rotation around this BF bond.

Magnetic susceptibility measurements down to 2 K and EPR spectroscopy showed the existence of weak super‐exchange interactions (|J| < 0.4 cm−1). These results are discussed in relation to the available structural information.
Spectral sensitization of SnO2 electrodes with Cu(I)‐based dyes
Authors: Breddels P. A. , Berdowski P. A. M. , Blasse G.
Published: September 2010

The spectral sensitization of SnO2 electrodes with some Cu(I) complexes is reported. Excitation into the metal‐to‐ligand charge transfer (MLCT) states gives rise to sensitized anodic photocurrents. The positions of the maxima in the action spectra depend on the ligands.
Isolation and synthesis of 3‐(2‐butenyl)‐2,4,4‐trimethyl‐2‐cyclohexen‐1‐one. Regiospecific oxidation of 1‐(2‐butenyl)‐2,6,6,‐trimethylcyclohexene
Authors: van der Weerdt Anton J. A. , Apeldoorn Willem , Boelens Mans , Könst Wil M. B. , Heide Roel Ter
Published: September 2010

(E)‐ and (Z)‐3‐(2‐butenyl)‐2,4,4‐trimethyl‐2‐cyclohexen‐1‐one 1 and 2 have been isolated from an absolue of Osmanthus Fragrance Lour. and a fusel oil concentrate. Structural proof for these compounds has been obtained via their synthesis from β‐ionone. The key step in this synthesis is the regio‐specific oxidation of 1‐(2‐butenyl)‐2,6,6‐trimethylcyclohexene.
Synthesis of thiazoles and imidazoles from isothiocyanates and tosylmethyl isocyanide. Base‐induced ring transformation of 5‐amino‐1,3‐thiazoles to imidazole‐5‐thiols
Authors: van Nispen Simon P. J. M. , Bregman Jacob H. , van Engen Douwe G. , van Leusen Albert M. , Saikachi Haruo , Kitagawa Tokujiro , Sasaki Hideaki
Published: September 2010

Base‐induced cycloadditions of tosylmethyl isocyanide to a series of isothiocyanates have been investigated. Depending on the reaction conditions, thiazoles 5 and/or imidazoles 7 are obtained, with the thiazoles, in particular, being obtained with high regiospecificity. During the course of this work a high‐yield ring transformation of 5‐amino‐1,3‐thiazoles (5) to imidazole‐5‐thiols (7) was discovered, which has not been previously reported. A number of reactions of 7 are described.
Ring inversion in some fully α‐methylated cycloalkane‐1,2‐diones
Authors: Verheidt Paul L. , Kruk Cor , Cerfontain Hans
Published: September 2010

Variable‐temperature NMR spectra of 3,5,5,5‐tetramethylcyclopentane‐1,2‐dione (1a) and its 6‐, 7‐ and 8‐membered homologues (1b‐d) showed conformational isomerization for the letter three compounds, the barrier to their ring inversion being 37.5, 38.9 and 62.7 kJ/mol, respectively.
Reduction of a 3,4‐cyclic‐substituted 2H‐1‐benzopyran‐2‐one with lithium in liquid ammonia
Authors: Driessen R. A. , Salemink C. A.
Published: September 2010

Reduction of the α,β‐unsaturated lactone system in 1‐hydroxy‐3‐pentyl‐7,8‐dihydro‐spiro[dibenzo[b,d]pyran‐9,2′‐[1,3]dioxolan]‐6(10H)‐one (3) with lithium in liquid ammonia leads to cis products.
The electrochemical reduction of diazanaphthalenes; a spectro‐electrochemical investigation
Authors: Wolsink J. H. , Spaans A. , van den Ham D. M. W. , Feil D.
Published: September 2010

The electrochemical reduction of diazanaphthalenes in dimethylformamide at first‐ and second‐wave diffusion levels has been investigated by means of transmission spectro‐electrochemical methods. It has been found that the reaction of dianions with parent neutral molecules is an essential step in the reaction mechanism. Rate constants for all non‐electrochemical steps have been measured or estimated.

Independent estimations of diffusion and absorbance coefficients are presented, as well as some principles of digital simulation.
Effects of γ‐hydroxyl groups in lithium‐ammonia reductions of α,β‐unsaturated carbonyl compounds via an inverse‐addition, low‐temperature method
Authors: de Groot Ae. , Jansen B. J. M. , Peterse A. G. J. M. , Wijnberg J. B. P. A.
Published: September 2010

A new inverse‐addition, low‐temperature procedure for lithium‐ammonia reductions has been developed. Using this method it has been demonstrated that the reduction of ethyl 5,5‐(ethylenedioxy)‐8β‐hydroxy‐4aβ‐methyl‐2‐oxo‐2,3,4,4a,5,6,7,8‐octahydro‐1‐naphthalenecarboxylate (3) results in an unusual cis‐reduction product. The 8β‐hydroxyl group, low reaction temperature (–80°C) and addition of lithium‐ammonia to the substrate all proved to be necessary in order to achieve this cis reduction.
Nouvelle synthèse et étude de la stabilité de l'amino‐3 thiophène
Authors: Rault S. , de Sevricourt M. Cugnon , Robba M.
Published: September 2010

A new synthesis of 3‐aminothiophene is proposed starting from 3‐thenoic acid via isopropyl 3‐thienylcarbamate as intermediate. Thermal decomposition of this latter in alkaline medium gives 3‐aminothiophene.

NMR and mass spectral studies revealed that the instability of the amine is due to its polymerisation via the formation of the dimer di‐3‐thienylamine and the trimer tri‐3‐thienylamine.
Studies on polypeptides XXXVII. Synthesis of [isoleucine‐13, homoserine‐20]‐s‐peptide lactone and semisynthesis of [isoleucine‐13, homoserine‐20]‐RNase A
Authors: Hoogerhout P. , Kerling K. E. T.
Published: September 2010

The solid‐phase synthesis of [Ile13, Met20]‐S‐peptide‐(Gly‐Gly) on a Merrifield resin, using tert‐butoxycarbonyl‐ and benzyl‐type protecting groups, is reported. Deprotection was achieved by reaction with liquid hydrogen fluoride and purification by ion‐exchange chromatography and HPLC.

The above peptide was converted into [Ile13, Hse20]‐S‐peptide lactone by reaction with cyanogen bromide. Reaction of the synthetic 20‐peptide lactone with “native” bovine S protein at pH 7.5 resulted in the formation of [Ile13, Hse20]‐RNase A in about 10% yield. The semisynthetic enzyme was purified by ion‐exchange chromatography and the kinetic parameters were determined from 2′,3′‐CMP hydrolysis.
1,3,4‐Trimethyl‐2,2′‐pyrromethen‐5[1H]‐one and its 1′‐methyl derivative; Synthesis, thermal and photochemical reactivity
Authors: de Groot J. A. , Lugtenburg J.
Published: September 2010

Condensation of 1,3,4‐trimethyl‐1,5‐dihydro‐2H‐pyrrol‐2‐one, prepared in high yield from 3,4‐dimethylpyrrole, with pyrrole‐2‐carboxaldehyde and 1‐methylpyrrole‐2‐carboxaldehyde gives a mixture of Z‐ and E‐1,3,4‐trimethyl‐2,2′‐pyrromethen‐5[1H]‐one (7 and 8) and 1,1′,3,4‐tetramethyl‐2,2′‐pyrromethen‐5[1H]‐one (9 and 10), respectively. The Z and E forms both isomerise thermally upon heating in basic methanol to the same equilibrium state as is observed during the synthesis. Upon irradiation with light (λ > 360 nm), 7, 8, 9 and 10, similarly undergo Z‐E isomerisation.
Synthesis of meso‐ and (±)‐2,2′‐bis(carboxymethoxy)oxydiacetic acid via cis‐ and trans‐2,5‐(diallyloxy)‐2,5‐dihydrofuran: Model compounds for the calcium complexation of oxidized sucrose
Authors: Nieuwenhuizen M. S. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

Cis‐ and trans‐2,5‐diallyloxy‐2,5‐dihydrofuran have been prepared by acid catalyzed transacetalization of 2,5‐dimethoxy‐2,5‐dihydrofuran with allyl alcohol. As a by‐product, 1,1,3‐triallyloxypropane was formed from 2‐allyloxy‐2,5‐dihydrofuran intermediates. The cis/trans configuration has been determined by NMR (chiral lanthanide shift reagent) and MS (elimination of allyl alcohol). Oxidation of the cis and trans compounds by potassium permanganate yielded meso‐ and (±)‐2,2′‐bis(carboxymethoxy)oxydiacetic acid, respectively. The calcium sequestering properties of the latter compounds were superior to those of the acetal polycarboxylate obtained by sucrose oxidation. This is due to the extra steric hindrance encountered for the latter upon calcium complexation.
N‐nitroso‐1,3‐oxazolidine, a carcinogenic compound detected as an impurity in a commercial cutting fluid
Authors: Ellen G. , Freudenthal J. , Schuller P. L.
Published: September 2010

The title N‐nitrosamine, a potent liver carcinogen, was detected in a mineral oil cutting fluid at concentrations up to 60 mg/kg. Identification was performed by gas chromatography/mass spectrometry and by synthesis. The compound is thought to have been formed from formaldehyde, sodium nitrite and an amino alcohol present in the cutting fluid.
Synthesis of some new pyrazole‐containing chelating agents
Authors: Driessen Willem L.
Published: September 2010

Procedures are described involving the condensation of l‐(hydroxymethyl)pyrazole (1a) and l‐(hydroxymethyl)‐3,5‐dimethylpyrazole (1b) with the following amines (products given in parentheses): ethylamine (2a and 2b), aniline (3a and 3b), N,N′‐dimethyl‐ l,2‐ethanediamine (4a and 4b), 1,2‐ethanediamine (6a and 6b), diethylenetriamine (7a and 7b), triethylenetetramine (8a and 8b) and ammonia (9a and 9b). All amine hydrogens are completely substituted by pyrazol‐1‐ylmethyl groups (compounds 2a‐9a) or (3,5‐dimethylpyrazol‐1‐yl)methyl groups (compounds 2b‐9b with yields being better than 90%.
Synthesis of linear and cyclic peptides related to Met‐ and Leu‐enkephalin
Authors: van Nispen J. W. , Greven H. M.
Published: September 2010

The synthesis is described of several peptides containing the sequence Phe‐Met. In order to limit enzymatic degradation and to restrict the number of possible conformations they were cyclized with variable ring size. Some unexpected side‐reactions were encountered during the synthesis of the linear precursors: partial cleavage of the active ester during removal of the Bocprotecting group, partial cleavage of the Gly‐Gly peptide bond during hydrazinolysis of an ester function and failure to obtain the p‐nitrophenyl ester of Boc‐Phe‐Met‐Gly‐Gly‐OH via the DCC method. Diphenyl phosphoroazidate was finally used for the cyclization of several linear peptides. Some results of behavioural activity and metabolic stability are mentioned.
On the luminescence and photochemistry of the lower excited electronic states of some acyclic 1,2‐diketones
Authors: Sarphatie Louis A. , Verheijdt Paul L. , Cerfontain Hans
Published: September 2010

The absorption and luminescence spectra of a number of acyclic 1,2‐diketones have been determined,viz. of 2,3‐butanedione, 2,2,5,5‐tetramethyl‐3,4‐hexanedione, some dicycloalkyl and of cyclopropyl‐ and phenyl‐substituted 1,2‐diketones. For the 1,2‐diketones without conjugating substituents, the time‐averaged ground‐state dihedral angles between the two carbonyl group (magnified image) have been estimated from the positions of the long‐wavelength UV absorption band. The variation in the fluorescence transition energy with the ground‐state dihedral anglemagnified imageis only small,viz. 1500 cm−1, on varyingmagnified imagefrom 0 to 180°. The difference between the fluorescence and phophorescence transition energies is independent of the ground statemagnified image. The results show that the 1,2‐diketones emit from excited states with coplanar diketo geometry.

The λ 403 nm photochemistry of 2,2,5,5‐tetramethyl‐3,4‐hexanedione (2) and dicyclopentyl‐ (6) and dicyclohexyl‐ethanedione (7) has been studied in some detail. The yields of the 2‐hydroxycyclobutanone products (14), formed by aNorrishtype II process of the triplet‐excited 1,2‐diketone, decrease in the substrate order2>6>7an explanation for this order is proposed.
Réactivité de cyclodi‐ et tri‐germazanes: Mise en évidence de la participation de germylèneamines dans des réactions d'insertion‐élimination
Authors: Lacrampe G. , Lavayssière H. , Riviére‐Baudet M. , Satgé J.
Published: September 2010

Les cyclogermazanes (R2GeNR′)n (n = 2, 3), formes polycondensées des germyléneamines R2Ge=NR′, sont obtenus par aminolyse ou ammonolyse des liaisons Ge‐Cl, par transamination intermoléculaire, ou par action des chlorures germaniés sur les aminodilithiens. Leur degré de condensation (n = 2, 3) est fortement lié à la nature des substituants portés par l'azote ou le germanium.

Les réactions de clivage par divers réactifs protoniques bifonctionnels tels que les diols, dithiols, aminoalcools, aminothiols, aminoacides ont été étudiées et conduisent aux hétérocycles germaniés à 5 chaînons correspondants, par clivage de 2 liaisons Ge‐N consécutives.

Les réactions d'insertion d'hétérocumulènes ou de dipǒles insaturés tels que RNCO, RNCS, CO2, CS2, PhCHO, et l'oxirane, conduisent à des réactions d'extension de cycle.

Les dérivés de diaddition des isocyanates et isothiocyanates aux cyclogermazanes se décomposent avec formation transitoire de germylèneamines mises en évidence dans leur réaction de cycloaddition 1‐2 avec les iso‐ ou isothio‐cyanates et formation de diazagermétidinones (ou thiones) instables.

De même, les dérivés d'addition des cyclogermazanes aux aldéhydes, CO2, CS2 conduisent aux cyclogermoxanes ou germathianes via les germanones et germathiones correspondantes.

Les dipǒles 1–3 tels que les nitrones régissent avec les cyclogermazanes à des températures voisines de 150°C avec formation transitoire de 1,3,5,2‐oxadiazagermolidines instables.

La réactivité des cyclodigermazanes est exaltée en présence de triéthylamine, de HMPT. La possibilité d'une participation de la forme monomère germylèneamine R2Ge=NR' dans ces dernières réactions, découlant d'un équilibre cyclodigermazane ⇋ germylèneamine est discutée.
The kinetics and primary isotope effect for reduction of acridinium ions by a NAD(P)H “model”; facts and fallacy
Authors: van Laar A. , van Ramesdonk H. J. , Verhoeven J. W.
Published: September 2010

A kinetic study of the reduction of the 10‐methyl‐9‐phenylacridinium ions (AcPh⊕) by 1‐benzyl‐1,4‐dihydronicotinamide (PyH2) is presented. The primary kinetic isotope effect (kH/kD = 4.5) of this reaction equals the product isotope partitioning observed upon reduction with mono C‐4 deuterated 1‐benzyl‐1,4‐dihydronicotinamide (PyHD). Furthermore, the rate constant for the reduction decreases upon increasing the solvent polarity. This behaviour contrasts with that reported for the reduction of the 10‐methylacridinium ion (AcH⊕) where acceleration due to increased solvent polarity and significant discrepancies between the kinetic isotope effect and the product isotope partitioning have been observed. Reinvestigation of the latter process by means of kinetic measurements and via a competition experiment, involving reduction with equal amounts of PyH2 and the dideuterated species (PyD2), shows that the kinetic data and especially the kinetic isotope effect data are easily subject to experimental error. Thus it is shown that an intolerable inaccuracy is introduced if the value of kH/kD is determined by comparing the rate of reduction with PyH2 with that of PyHD rather than by comparing those of PyH2 and PyD2. Furthermore, the kinetic data in protic solvents for AcH⊕, but not for AcPh⊕, are found to be disturbed by a reversible side reaction. This reaction is thought to involve formation of a covalent adduct by attack of PyH2 at the electrophilic C‐9 position of AcH⊕. The less electrophilic nature of this position in AcPh⊕ prevents such adduct formation and leads to uncomplicated kinetic behaviour in all the solvent systems investigated.
The conformational equilibria of 1‐ and 2‐phenyl‐1,2‐dihydronaphthalene
Authors: Lamberts J. J. M. , Laarhoven W. H.
Published: September 2010

The conformational equilibria of 1‐ and 2‐phenyl‐1,2‐dihydronaphthalene (1 and 2) have been studied using 500 MHz 1H NMR spectroscopy.

The signals due to the protons at C(1) and C(2) of compound 2 and of a deuterated derivative of 1 (3,4‐d2‐1) were analysed as ABX patterns. The fraction x of the conformer, having the phenyl group in a pseudo‐axial (pa) position, was found to be 0.44 for 3,4‐d2‐1, in contrast to the marked preference shown by non‐aromatic substituents at C(1) of 1,2‐dihydronaphthalenes for the pa position. This difference is most probably due to π‐overlap between a pseudo‐equatorial phenyl substituent and the aromatic moiety of the 1,2‐dihydronaphthalene counterbalancing the peri‐interaction with H(8).

For 2, x = 0.31, indicating a slight preference of the phenyl group for the pseudo‐equatorial (pe) position which preference is also observed for other substituents at C(2) of 1,2‐dihydronaphthalenes.
Exchange processes in spirophosphoranes with a dioxaphosphorinane ring. A 13C and 1H NMR study
Authors: van Ool Peter J. J. M. , Buck Henk M.
Published: September 2010

Variable temperature 13C and 1H NMR studies have revealed the equatorial‐apical preference of dioxaphosphorinane rings in pentacoordinated trigonal bipyramidal spirophosphoranes.