bluuebunny/crossref_metadata_2025 huggingface dataset:
Unconventional nucleotide analogues. V Derivatives of 6‐(1‐pyrimidinyl)‐ and 6‐(9‐purinyl)‐2‐aminocaproic acid
Authors: de Koning H. , Pandit U.K.
Published: September 2010

Base‐catalyzed condensation of Nα‐benzyloxycarbonyl‐D,L‐lysine (1) with acrylamides 2a, b led to the formation of 2‐benzyloxy carbonylamino‐6‐(1‐pyrimidinyl)caproic acids 3a, b in good yields. Hydrolysis of 3a, b yielded the corresponding amino acids 4a, b. 6‐Chloropurine (9b) reacted with bromide 6b to give the N(9)‐ and N(7)‐substituted purines (10d and 11d). Subjecting 10d to the sequence: amination, hydrolytic decarboxylation, and deformylation, gave 6‐(9‐adeninyl)‐2‐aminocaproic acid 12a.
Stereoselective synthesis of eremophilane sesquiterpenoids from β‐pinene
Authors: van Der Gen A. , van Der Linde L. M. , Witteveen J. G. , Boelens H.
Published: September 2010

2‐Methyl‐4‐isopropylidenecyclohexanone (7) can be obtained in good yield from β‐pinene (2) in a 5‐step sequence. Key step is the acid‐catalysed ring opening of cis‐3‐methylnopinone (5) to give 4‐(l′‐hydroxyisopropyl)‐2‐methylcyclohexanone (6, XOH). Robinson annulation of 7 with trans‐3‐penten‐2‐one proceeds stereoselectively to give α‐vetivone (10). Similar annulation of the isopropenyl isomer (8) affords 7‐epi‐nootkatone (11). 10 can be converted in good yield to nootkatone (13).
The nitration of mono‐alkylbenzenes conformational analysis and steric hindrance: Part II: Secondary alkylbenzenes
Authors: Baas J.M.A. , Wepster B.M.
Published: September 2010

The isomer distributions for the nitration of six secondary alkylbenzenes and the partial rate factors of three of these compounds have been determined. The steric hindrance of the nitration in the ortho‐position of isopropylbenzene is mainly of an enthalpic nature. The increase of this hindrance in the series of isopropylbenzene, s‐butylbenzene, (1‐ethylpropyl)benzene is of an entropic nature and can be explained from the conformational analysis of the initial states and the transition states. The steric hindrance in the ortho‐positions of (2‐methyl‐1‐ isopropylpropyl)benzene and (1‐t‐butyl‐2.2‐dimethylpropyl)benzene is very large.
The coordination chemistry of phenylbisdimethylaminophosphine oxide
Authors: de Bolster M.W.G. , Groeneveld W.L.
Published: September 2010

A number of new solvates and adducts containing phenylbisdimethylaminophosphine oxide is reported. The solvates have the general formula M{C6H5P(O)‐[N(CH3)2]2}42+(anion)22−, in which M = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn and Cd, and the anions are ClO4− and BF4−. The adducts have the general formula MCl2{C6H5P(O)[N(CH3)2]2}n, in which M = Mg, Ca, Mn, Co, Ni, Cu, Zn and Cd, and n = 2, except for the Cd compound in which n = 3.

The compounds are characterized and identified by chemical analyses and physical measurements.

Vibrational spectra in the region 4000‐200 cm−1 have been investigated. A tentative assignment is proposed and the shifts of some ligand bands upon complexing are discussed. It is concluded that coordination takes place via the oxygen atom.

Ligand‐field spectra for the complexes of Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) have been investigated. Values for the ligand‐field parameters are reported.

X‐ray powder patterns were used in combination with ligand‐field spectra to deduce the coordination around the metal ions.

By a comparison of the ligand properties of phenylbisdimethylaminophosphine oxide, hexamethylphosphoramide and triphenylphosphine oxide the importance of steric factors in coordination chemistry is again demonstrated.
Synthesis of 4‐alkyl‐2‐hydroxy‐2‐methyl‐4‐butanolides and 4‐alkyl‐2‐methyl‐2‐buten‐4‐olides
Authors: Klaren‐De Wit M. , Frost D. J. , Ward J. P.
Published: September 2010

4‐Ethyl‐ and 4‐isobutyl‐2‐methyl‐2‐buten‐4‐olide have been prepared by reaction of 2‐butanone and 4‐methyl‐2‐pentanone with sodium pyruvate, followed by reduction of the 2‐hydroxy‐2‐methyl‐4‐oxoalkanoic acids obtained, and lactonization to 4‐alkyl‐2‐hydroxy‐2‐methyl‐4‐butanolides. Treatment with triphenylphosphine in carbon tetrachloride caused extensive desaturation.

The stereochemistry of the cyclic hydroxy and chloro intermediates was determined from the 220 MHz NMR spectra of the 4‐isobutyl derivatives.
Isomerisation of s‐triazolo [3,4‐a]isoquinoline and s‐triazolo[4,3‐a]thieno[3,2‐c]pyridine
Authors: Hoogzand C.
Published: September 2010

The novel heterocyclic compounds s‐triazolo[5,1‐a]isoquinoline, IIa, and s‐triazolo [3,2‐c]pyridine, IV, together with a few derivatives have been synthesized by isomerisation of the corresponding [3,4‐a] isomers by base in ethylene glycol/water. The spectral properties are discussed.
Pyrazoles and imidazoles as ligands. Part VII.N‐n‐butylimidazole as a ligand to metal(II) halides and isothiocyanates
Authors: Reedijk J.
Published: September 2010

A number of compounds of formula M(Nn BuIz)n(anion)2 are described, the metal ions being Mn, Fe, Co, Ni, Cu, Zn and Cd and the anions Cl−, Br−, I− and NCS−; Nn BuIz stands for N‐n‐butylimidazole and n = 1–6.

The compounds are prepared from the corresponding metal salts and the ligand in ethanol, and are characterized by chemical analyses and physical measurements.

The ligand Nn BuIz is shown to coordinate with metal ions via the lone pair electrons of the pyridine‐nitrogen of the five‐membered ring. Metal(II) ions are found to be (pseudo)‐octahedral six coordinate for all compounds having n = 6 and n = 4, and for the Cu(II) compounds with n = 1 and 2. The remaining compounds with n = 2 have tetrahedrally coordinated metal ions.
Pyrazoles and imidazoles as ligands. Part VIII: Mössbauer spectra of octahedral Fe(II) solvates containing substituted pyrazoles and imidazoles as ligands
Authors: Reedijk J.
Published: September 2010

Mössbauer spectra are reported and discussed for a number of compounds of formula Fe(ligand)6(anion)2, with pyrazole, 3(5)‐methylpyrazole, imidazole, N‐methylimidazole and N‐n‐ butylimidazole as ligands, and ClO4−, Br− and I− as anions.

The values found for the isomer shift (δ) and the quadrupole splitting (ΔEq) are in agreement with high‐spin iron(II) in a distorted octahedral coordination.

The magnitude of δ, being 1.32 ± 0.02 mm/s, in these compounds is rather small and occurs at the lower site of the range usually found for octahedral iron(II).

For closely resembling compounds a relation is found between ΔEq and the value of the magnetic moment.

The author is indebted to Drs. D. W. Engelfriet, D. Knetch and Ir. A. M. van der Kraan for assistance with the measurements, and to Dr. A. M. van der Kraan for assistance with the measurements, and to Dr. W. L. Groeneveld for his interest in this study.
Resolution, optical rotatory dispersion, and absolute configuration of 1,3‐bis(2‐piperidyl)propan‐2‐one (anaferine)
Authors: Beyerman H. C. , Maat L. , Moerman C. A.
Published: September 2010

(±)‐1,3‐Bis(2‐piperidyl)propan‐2‐one was resolved with the aid of the enantiomeric 6,6′‐dinitrobiphenyl‐2,2′‐dicarboxylic acids. Both optical rotatory dispersion measurements and chemical correlation showed the laevo‐rotatory compound to be (‐)‐(R,R)‐1,3‐bis(2‐piperidyl)propan‐2‐one, (‐)‐anaferine.
Sulfonyl‐stabilized phosphonium ylids
Authors: van Leusen A. M. , Reith B. A. , Iedema A. J. W. , Strating J.
Published: September 2010

Two general methods are given for the synthesis of mono‐sulfonyl‐substituted methylenephosphoranes, magnified image (1). (i) Methylenetriphenylphosphorane can be substituted by using sulfonyl fluorides to give 1. A similar reaction with sulfonyl chlorides, however, fails mostly, (ii) The synthesis of sulfonylmethyltriphenylphosphonium bromides (5) from bromomethyl sulfones and triphenylphosphine, due to Speziale and Ratts, was improved. The bromides 5 were readily transformed to 1 by base.

As an extension of (i), the reaction of benzylidenetriphenylphosphoranes with sulfonyl halides has been studied. Contrary to previous reports it was found that the product from ethoxycarbonylmethylenetriphenylphosphorane and tosyl chloride is α‐ethoxycarbonyl‐p‐tolylthiomethylenetriphenylphosphorane, instead of the corresponding tosyl compound. Method (i), however, does not apply to ethoxycarbonylmethylenetriphenylphosphorane (16).
Electron spin resonance of complexes of pentacyanocobaltate(II) with aromatic nitro and nitroso compounds
Authors: Basters J.
Published: September 2010

By means of ESR techniques a systematic study has been made of radicals prepared by reaction of aromatic nitro and nitroso compounds with pentacyanocobaltate(II). Assignments of hyperfine coupling constants have been confirmed by deuterium substitution. The structure of the radicals, aryl pentacyanocobalt nitroxides, has been confirmed by experiments with nitro, corresponding nitroso and dinitro compounds and experiments with varying cobalt‐substrate ratio. Substituent effects on the nitrogen hyperfine interactions have been expressed in terms of a Hammett relationship aN = −1.46 σ ± 13.79. A qualitative ligand‐field model is given to get a better understanding of the delocalization of the unpaired electron over the transition metal ion and the aromatic ligand.
Chemistry of acetylenic ethers 95: Photochemical additions of acetylenes II reactions of ketones with 1‐alkynyl ethers
Authors: Bos H. J. T. , van der Bend H. T. , Boleij J. S. M. , Everaars C. J. A. , Polman H.
Published: September 2010

Photoaddition of aromatic ketones to 1‐alkynyl ethers R ′O ‐ C  C ‐ R generally affords, via C3O‐cycloaddition (oxete derivatives) alkyl 3,3‐diarylacrylates: Ar2C = CR ‐ COOR′in good yields (R = H,CH3,C2H5;R′ = CH3,C2H5).

Analogously from acetone and 1‐methoxy‐1‐propyne, methyl 2,3‐dimethyl‐2‐butenoate (CH3)2C = C(CH3)COOCH3 was obtained, together with RH‐adduct III and an isomerised analogue IV.

In two cases some 1,3,5‐triethoxybenzene, resulting from trimerisation of ethoxyethyne, could be isolated.
CIS‐ and trans‐1‐chloropropene vibrational assignment; coriolis interaction
Authors: Berg G. C. V. D. , Elst R.
Published: September 2010

Infrared spectra of the gaseous state and Raman spectra of the liquid state of cis‐ and trans‐1‐chloropropene are recorded in the 100‐4000 cm−1 region. Vibrational assignments are given for both isomers.

Vibration‐rotational analysis of the spectrum of trans‐1‐chloropropene made it possible to calculate four Coriolis coupling constants.
Solutes in sulfuric acid 4: Ionization of arenesulfonic acids; determination of pKa values by UV techniques
Authors: Cerfontain H. , Schnitger B. W.
Published: September 2010

The ionization of several aromatic sulfonic acids in aqueous sulfuric acid has been measured by means of UV techniques. The sulfonic acid ionization does not follow the aniline Ho acidity function, but the benzophenone Hao and the HA acidity functions. On the basis of the Hao scale, the pKa of benzenesulfonic acid is −6.65 ± 0.05. Substituent effects on the ionization of the sulfonic acid group are small; the Hammett ρ‐value was estimated to be 0.7 ± 0.2.
Liquid‐phase CO‐oxidation of aldehydes and olefins radical versus non‐radical epoxidation
Authors: Vreugdenhil A. D. , Reit H.
Published: September 2010

In co‐oxidations of aldehydes and olefins with molecular oxygen in the liquid phase, epoxides are formed via two different routes: (1) by reaction of intermediate acylperoxy radicals with the olefin, and (2) by a non‐radical reaction of intermediate peracid with the olefin. For the systems benzaldehydecis‐1, 2‐D2‐1‐octene and benzaldehydecis‐ andtrans‐2‐octene the ratio of radical to non‐radical epoxidation has been calculated with the aid of the kinetic relationships derived for this type of reaction and has been determined experimentally from the stereo selectivity of the expoxidation and from the production of carbon dioxide. The results show that the ratio of radical to non‐radical epoxidation increases with increasing reactivity of the olefin as well with increasing olefin/aldehyde ratio.
Studies of inter‐ and intra‐molecular donor‐acceptor interactions ‐ X: Intramolecular Charge transfer interaction in substituted N‐aralkyl‐phthalimides and ‐1,8‐naphthalimides
Authors: Craenen H. A. H. , Verhoeven J. W. , de Boer Th. J.
Published: September 2010

Compounds D‐(CH2)n‐A (n = 1‐5) are studied, in which D = an aromatic group with low ionization potential (e.g. an electron donor) and A is mainly the N‐3,6‐dinitro‐1,8‐naphthalimide group. Especially for n = 1 and n = 3, interaction between D and A leads to the observation of discrete intramolecular C(harge) T(ransfer) transitions in the electronic absorption spectra. For n = 1 this is explained by “homoconjugative” interaction, while for n = 3 the molecules probably adopt a folded conformation, a suggestion which is suppported by NMR data. For n = 2 close approach of D and A seems to be sterically excluded, while for n > 3 the interaction between D and A rapidly diminishes. For the compound with D = 9‐anthryl and n = 3 steric interaction between the peri‐hydrogens of the anthryl group and the trimethylene chain seems to inhibit the molecule from adopting a folded conformation. For the compounds with D = p‐dimethylaminophenyl and n = 3 or 4 a double intramolecular CT transition is observed; a tentative explanation for this phenomenon is given.
Réactions D'Hétérocycles Oxygénés avec les Trialcoylsilyl‐, ‐Germyl‐ et ‐Stannyl‐Phosphines: II. Cas des lactones et des anhydrides d'acide
Authors: Couret C. , Escudié J. , Satgé J.
Published: September 2010

The trialkyl‐silyl‐, ‐germyl‐ and ‐stannyl‐phosphines R3MPEt2 react with β‐propiolactone via the cleavage of the alkyl‐oxygen bond of the lactone, leading to the trialkylmetal β‐diethylphosphinopropionates R3MOCOCH2CH2PEt2 (M = Si, Ge, Sn). These reactions are accompanied by a strong polymerization of the β‐propiolactone.

The germyl‐ and silyl‐phosphines cleave γ‐butyrolactone at a rather high temperature and in the presence of catalyst (ZnCl2). Only the acyl‐oxygen scission is observed in this case, with formation of the phosphorated kétoalkoxymetal derivatives R3MO(CH2)3COPEt2. Under the same conditions, the stannylphosphines decompose before reacting.

In the case of the hydrosilylphosphines R2(H)SiPEt2, the kétoalkoxymetal derivative cyclises by intramolecular addition SiH/C=O with formation of 2‐sila‐1,3‐dioxepane with a phosphorated substituent: magnified image

The same acyl‐oxygen cleavage is observed in the action of the metal‐IVb phosphines on succinic anhydride to lead to the kétoesters R3MOCO (CH2)2COPEt2 (M = Si, Ge, Sn). The action of the hydro‐germyl‐ or ‐silyl‐phosphines R2(H)MPEt2 leads, in a first phase, to the corresponding γ‐kétoesters R2(H)MOCOCH2CH2COPEt2 which cyclise via intramolecular addition with formation of cyclic germa‐ or sila‐alkoxy esters. magnified image
Chemistry of sulfines. XII: Cyclo‐addition reactions with dienes
Authors: Zwanenburg B. , Thijs L. , Broens J. B. , Strating J.
Published: September 2010

The cyclo‐addition reaction of sulfines with 1,3‐dienes is described. In all cases studied six‐membered ring sulfoxides were formed (Schemes I, II and III). Sulfines with electron‐withdrawing substituents, such as dichlorosulfine, appeared to be very reactive dienophiles. The stereochemistry of the reaction was studied with Z‐ and E‐chloro‐phenylsulfine and 2,3‐dimethyl‐1,3‐butadiene. The results show that the stereochemical configuration of the starting sulfine is predominantly retained in the (2 + 4) cyclo‐adduct.
Pyrazoles and imidazoles as ligands. Part XII: Metal (II) perchlorates and tetrafluoroborates containing 2‐methylimidazole as ligand
Authors: Reedijk J.
Published: September 2010

Several complexes of general formula M(2MIz)n(anion)2, with M = Mn, Fe, Co, Ni, Cu, Zn and Cd are reported. The anions are ClO−4 and BF−4, n = 4 or 6, and 2MIz stands for 2‐methylimidazole.

The compounds are prepared from alcoholic solutions of the ligand and the metal salt in the presence of triethyl orthoformate.

Structural conclusions are drawn from infrared spectra, ligand‐field spectra, X‐ray powder diagrams and paramagnetic resonance measurements.

Depending upon the particular cation, the metal ions were found to be tetragonally (Mn, Fe, Cd), tetrahedrally (Co, Zn), square planar (Cu, Ni), or octahedrally (Cd) coordinated. In the tetragonal compounds the ClO−4 and BF−4 anions are very weakly coordinated to the metal ions. No anion coordination occurs in the remaining compounds.
Interpretation of E.P.R.‐Spectra of powdered octahedral nickel(II) complexes with nitrogen‐donor ligands
Authors: Reedijk J. , Nieuwenhuijse B.
Published: September 2010

Calculation methods for the evaluation of the parameters g, D and E for an S = 1 system, from paramagnetic resonance powder spectra are discussed and applied to a number of compounds having the general formula Ni(ligand)6(anion)2; in this formula the ligands are nitrogen donors such as nitriles, pyrazoles and imidazoles, with large anions like ClO−4, BF−4, SbCl−6, InBr−4 and GaCl−4.

A treatment similar to that of organic triplet molecules can be used for the interpretation, despite the fact that the observed bands are rather broad.

In the present compounds the g‐values were found to be isotropic within experimental error in the region 2.17‐2.20; the D‐values varied from 0.05‐0.90 cm−1 in the several compounds. The rhombic distortion (usually expressed as λ = E/D) was found to be small for most compounds, although λ‐values of 0.10, 0.16 and 0.33 were also found.
The X‐ray photoelectron spectrum of benzotris [c]‐2‐oxyfurazan (“hexanitrosobenzene”)
Authors: Bus J.
Published: September 2010

In order to confirm the multiple ring structure of benzotris[c]‐2‐oxyfurazan (“hexanitrosobenzene”), the electron‐binding energies of carbon, nitrogen and oxygen in this compound have been measured by X‐ray photoelectron spectroscopy. Charge calculations have been carried out by various methods for the interpretation of the results.

For each type of atom the 1s electron energy peak was split into two peaks of approximately equal intensity: carbon, 285.6 and 287.5 eV; nitrogen, 401.3 and 405.0 eV; oxygen, 533.4 and 535.0 eV. The carbon values may be less reliable because of deposition of pump oil onto the sample.

These results exclude the hexanitroso structure and support the furazan structure for which further evidence has already been published.
Formation of 2H‐thiopyrans and thiophenes by thermal rearrangement of propargyl vinyl sulfide or its homologues and 2‐alkynyl thienyl sulfides
Authors: Schuijl‐Laros D. , Schuijl P. J. W. , Brandsma L.
Published: September 2010

2H‐Thiopyran and a number of derivatives have been obtained in fair to good yields by heating compounds containing the system C ≡ CCSCC, in hexamethylphosphorictriamide. Mixtures of 2H‐thiopyrans and thiophenes are formed when heating is performed in this solvent or in dimethyl sulfoxide in the presence of amines. Thiopyrans, having an alkyl group on ring carbon atom 4, are partly converted into the “exo”‐compounds 4‐alkylidene‐2,3‐dihydro‐4H‐thiopyrans.
Inductive effects on benzene solvent shifts in PMR spectra of (acetylacetonato)‐organoantimony(V) and BIS(acetylacetonato)organotin(IV) compounds
Authors: Mackor A. , Meinema H. A.
Published: September 2010

PMR benzene solvent shifts
equation image
and
equation image
have been measured for acetylacetonato protons of hexacoordinate (acetylacetonato)organoantimony(V) and bis(acetylacetonato)organotin(IV) compounds. The observed values correlate better with the inductive effect of substituents at the metal atom than with the molecular dipole moments of these compounds. It is demonstrated that this relation holds also for tetrahedral compounds. The stereochemistry of the benzene‐acetylacetonato group interaction is discussed.
A thermochemical study of some tetra‐alkylammonium bromides in N,N‐dimethylformamide at 25°C
Authors: de Visser C. , Somsen G.
Published: September 2010

Enthalpies of solution of some tetra‐alkylammonium bromides (R4NBr, R = ethyl, n‐propyl and n‐butyl) have been determined in N,N‐dimethylformamide (DMF). The concentration‐dependence of the measured heats of solution can be readily accounted for by ionic association, so that measurements at very low concentrations could be avoided. The enthalpies of transfer from water to DMF of the tetra‐alkylammonium bromides deviate substantially from those reported for the corresponding iodides. The differences can be attributed to different transfer enthalpies of the iodide and bromide ions. The enthalpies of transfer of both alkali and tetra‐alkylammonium ions from N‐methylformamide and N‐methylacetamide to DMF are virtually constant, just like those from water and formamide to DMF when the enthalpic effect of solvophobic interaction is taken into account.
Model studies for enzyme inhibition. Part IV: The association of some alkyl methylphosphonates with α‐cyclodextrin in an aqueous medium
Authors: van Hooidonk C. , Breebaart‐Hansen J. C. A. E.
Published: September 2010

The formation of 1:1 inclusion complexes of some alkyl methylphosphonates with α‐cyclodextrin in an aqueous acidic medium has been established. The dissociation constants (Kdiss) of the inclusion complexes have been determined at 25°. The result indicate that non‐polar groups favour the inclusion process.

In one case stereospecificity in the formation of the inclusion complex was observed.
Addition des Thiols sur les Cétones. (I): Mécanisme de la réaction d'addition du mercapto‐éthanol sur la cyclohexanone
Authors: Fournier Messieurs L. , Natat A. , Lamaty Messieurs G. , Roque J. P.
Published: September 2010

The addition reaction of mercapto‐ethanol to cyclohexanone has been measured at 27.0° in solvant Ethanol‐Water “50/50”. The influence of initial thiol and hydronium ion concentrations on the rate of addition and on the equilibrium constant has been especially examined.

The reaction obeys general acid catalysis and general base catalysis; the thiol plays a dual role, acting both as a nucleophile and a general base. A mechanism is proposed for this reaction.
Properties of cyclodextrins: Part IX Specific inclusion compound formation of cyclodextrin derivatives with hexane and 2,3‐dimethylbutane in aqueous solution
Authors: Lammers J. N. J. J.
Published: September 2010

On the basis of thermodynamic data concerning inclusion compounds of α and β‐cyclodextrin derivatives with hexane (hex) and 2,3‐dimethylbutane (DMB) in aqueous solution, as reported in earlier publications in this series, a model of the inclusion complex is suggested. This model comprises:

A real inclusion compound (“fit in”) is formed in solution.

Almost all derivatives form inclusion compounds with hex and DMB in which the mole ratio is 1:1 (conclusion of Part VIII of this series).

α‐Cyclodextrin derivatives include in the voids hex molecules in their stretched form, whereas DMB molecules do not fit entirely into the voids. In both cases this causes a considerable disturbance in the water structure around the cyclodextrin molecules.

β‐Cyclodextrin derivatives include hex molecules in their coiled form and DMB molecules fit entirely into the voids. The water structure is hardly affected.

This model appears to be in agreement with considerations of space filling of the guest molecules in the cyclodextrin voids. Furthermore, in comparing the inclusion process with the dissolution of apolar compounds in different solvents, the model is confirmed. Also, comparison of the interaction among the different cyclodextrin derivatives is in agreement with the model.
Reaction of methylpyrazinecarbonitriles and 2‐methylquinoxaline with phosphorus oxychloride and organomagnesium compounds
Authors: Schwaiger W. , Ward J. P.
Published: September 2010

In the preparation of methyl methylpyrazinyl ketones by the sequence methyl‐pyrazinecarboxylic ester, amide, nitrile, to ketone, methylpyrazinecarbonitriles were found to react with phosphorus oxychloride forming tricyclic compounds related to “2‐methylquinoxaline orange”. 2‐Methylpyrazine‐6‐carbonitrile with methylmagnesium iodide underwent addition at one of the ring CN bonds. 2‐Methylquinoxaline reacted similarly with phosphorus oxychloride, and organomagnesium compounds. The methyl methylpyrazinyl ketone described in literature as the 2,6‐isomer was shown to be the 2,5‐isomer.
Chemistry and spectroscopy in strongly acidic solutions. XXXVIII: Stereoisomers interconversion of hexamethylcyclohexenyl cations via a transannular 1,3‐hydride shift
Authors: Hogeveen H. , Kiffen A. A.
Published: September 2010

The mechanism of stereoisomeric interconversion of hexamethylcyclohexenyl cations has been shown to involve two consecutive hydride shifts: a 1,2‐ and a transannular 1,3‐H shift.
Vibrational spectra and structure(s) of X(OR)4 molecules with X  C,: Si and R = methyl, ethyl
Authors: Ypenburg J. W. , Gerding H.
Published: September 2010

Vibrational spectra of tetramethoxymethane (TMM), tetraethoxymethane (TEM), tetramethoxysilane (TMS) and tetraethoxysilane (TES) have been recorded and assigned. DTA curves and temperature vs. time curves have been recorded in the region −150 to + 30°. No transition points have been observed, melting ranges are −1 to +2 (TMM); −16 to −12 (TEM); +10 to +16 (TMS) and −71 to −68° (TES).

The liquid state of tetramethoxymethane (TMM) contains two rotamers; the skeleton C(OC)4 may have S4 or D2d symmetry. The S4 form is about 1 kcal/mole more stable than the D2d form of TMM in the liquid. Solid TMM consists probably of the D2d configuration only.

There is no distinction between either configuration in tetramethoxysilane (TMS) as the rotation of methoxy groups around their SiO axes is apparently free for practical purposes.

The methyl group of an ethoxy group in X(OC2H5)4 may occupy a gauche or a trans position relative to its XO bond. Rotational isomerism of this kind is probably present in tetraethoxymethane (TEM).

Rotational isomerism is probably absent in tetraethoxysilane (TES).
Conformational analysis of some alkyl groups on benzene: PMR spectra of 4‐alkyl‐2‐nitroacetanilides
Authors: Baas J. M. A.
Published: September 2010

The PMR spectra of 2‐nitroacetanilide and often 4‐alkyl substituted derivatives have been measured. Two about equally stable conformers have been detected for the derivatives with the groups ‐CHPriBut, ‐CHBut2, and ‐C(OH)But2. The conformational isomerism is caused by a hindered rotation about the bond between the alkyl groups and the benzene ring; rotational barriers have been determined of approximately 12, 22, and 21 kcal/mole, respectively. The preferred conformations and the rotational barriers are discussed for the alkyl groups ‐CH2But, ‐CHMeBut, and ‐CHPri2.
Chemistry of sulfines, XIV: Benzo[b]thiophene derivatives from dichlorosulfine and diaryldiazomethanes
Authors: Thijs L. , Strating J. , Zwanenburg B.
Published: September 2010

The reaction of dichlorosulfine (Cl2C = S = O) with diaryldiazomethanes, (XC6H4)2C=N2 (X = H, 4‐CH3, 4‐Cl, 3‐OCH3) leads to derivatives of 2‐chlorobenzo[6]thiophene 1‐oxides. The reaction is proposed to proceed via cyclization of an intermediate episulfoxide. Oxidation of 2,2‐dichloro‐3,3‐diphenylthiirane with m‐chloroperbenzoic acid yields 2‐chloro‐3‐phenyl‐benzo[b]thiophene 1,1‐dioxide. This result supports the proposed cyclization mechanism.
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (XXVI): A 15N‐ and 14C‐study of the conversion of chloropyrazine into imidazole with potassium amide in liquid ammonia
Authors: Lont P. J. , van Der Plas H. C. , Bosma E.
Published: September 2010

The mechanism of the conversion of chloropyrazine into imidazole by potassium amide in liquid ammonia has been investigated. It has been proved, using the labelled compounds 2‐chloro‐[1‐15N]pyrazine and 2‐chloro‐[2‐14C]pyrazine, that this ring contraction occurs by a nucleophilic attack of the amide ion on position 3.

The synthesis of 2‐chloro‐[2‐14C]pyrazine starting from diethyl malonate labelled in the ethoxycarbonyl group, is described.
NMR Spectra of partially oriented mono‐ and hexa‐fluorobenzene
Authors: Gerritsen J. , Maclean C.
Published: September 2010

NMR spectra of fluorobenzene, partially oriented in two different liquid crystals have been measured and interpreted. It is shown that pseudo‐dipolar proton‐fluorine couplings can be neglected in deducing geometrical data from these spectra.

From the spectra of partially oriented hexafluorobenzene the indirect nuclear spin‐spin couplings have been determined.
Synthesis of tetra‐alkoxy‐ and tetra‐aryloxyethenes
Authors: Scheeren J. W. , Staps R. J. F. M. , Nivard R. J. F.
Published: September 2010

Several tetra‐alkoxyethenes have been synthesized from dialkoxy‐monoaryl‐oxymethanes by treatment with sodium hydride. The occurrence of dialkoxy carbenes as possible reaction intermediates is discussed. Best results (45‐60%) were obtained with dialkoxy‐mono‐p‐chlorophenoxymethanes.

Tetra‐aryloxyethenes have been prepared by a similar procedure in which diaryloxymethyl chlorides were used as starting compounds.
Vapour phase chemistry of arenes. I: Thermolysis of benzene and derivatives; the effect of additives. Evidence for free radical chain processes
Authors: Louw R. , Lucas H. J.
Published: September 2010

The rate of the conversion of benzene into biphenyl (“tank flow” reactor, atmospheric pressure, nitrogen dilution, 540°) is found to be highly dependent on type and concentration of additives. For example, small amounts of sulfur or oxygen lead to strong retardation, but a little formaldehyde or C2Cl6 has a profound accelerating effect. Wall (memory) effects are also observed.

These facts point to a radical chain mechanism ‐ involving H· and phenyl radicals ‐ rather than to a (bi)molecular process as was recently proposed by Fields and Meyerson. Other phenomena (H/D exchange, oxidation to phenol) are also consonant with a (semi)quantitative description based on thermo‐chemical kinetics.

The thermolysis of other arenes can be explained analogously; thus, biphenyl (giving benzene, ter‐ and quater‐phenyls) forms H·, C6H5‐C6H4· and phenyl radicals as intermediates, the latter fragments arising through H· + biphenyl → (C6H6‐C6H·5.→ benzene + phenyl.
Polyisocyanides, synthesis and isomerization to polycyanides
Authors: Nolte R. J. M. , Stephany R. W. , Drenth W.
Published: September 2010

Ni(C2H5OH) (t‐C4H9NC)Cl2 and nickel acetylacetonate are effective catalysts for the polymerization of isocyanides. Protic solvents and the presence of an acid accelerate the polymerization in case of nickel acetylacetonate. The reaction products are characterized as poly‐Schiff bases. Upon treatment with acid the polymers of primary alkyl isocyanides rearrange to polycyanides.
Studies on polypeptides xiv synthesis of possible rennin substrates
Authors: Schattenkerk Cecile , Voskuyl‐Holtkamp Ingrid , Bokhorst Ria
Published: September 2010

Leu‐Ser‐Phe‐Met‐Ala‐Ile‐Pro‐Pro‐Lys‐Lys and 14 smaller peptide fragments simulating increasing parts of the sequence around the rennin sensitive Phe‐Met bond in k‐casein have been synthesized and characterized.
On the mechanism of the amination of 4‐bromo‐2,6‐diphenyl‐ and 4,5‐dibromo‐2,6‐diphenyl‐pyrimidine with potassium amide in liquid ammonia
Authors: de Valk J. , van der Plas H. C.
Published: September 2010

It has been found that the amination of 4‐bromo‐2,6‐diphenylpyrimidine into the corresponding 4‐amino compound with potassium amide in liquid ammonia at −33° does not occur by the ANRORC‐mechanism but by an EA and/or AE‐mechanism. Treatment of 4,5‐dibromo‐2,6‐diphenylpyrimidine with potassium amide under the above‐mentioned conditions leads to a mixture of 4‐amino‐5‐bromo‐2,6‐diphenylpyrimidine and 4‐amino‐2,6‐diphenylpyrimidine. Evidence is presented that in the formation of 4‐amino‐5‐bromo‐2,6‐diphenylpyrimidine the ANRORC‐mechanism is operative to the extent of about 20%. The synthesis of the 1(3)‐15N‐enriched 4‐bromo‐2,6‐diphenyl‐ and the 4,5‐dibromo‐2,6‐diphenyl‐pyrimidine is described.
The crystal structure of 8‐methoxy‐N‐tosyl‐3‐trichloromethyl‐2,3,4,4a,5,6‐hexahydrobenzo[f]quinoline
Authors: van der Meer H.
Published: September 2010

This compound crystallizes in space group P21/c with cell constants a = 13.968, b = 19.395, c = 16.575, β = 90.37°, Z = 8. The crystal structure was determined in order to check the interpretation of NMR‐spectra.
Homogeneous hydrogenation of substituted cis‐cinnamic acids with pentacyanocobaltate(II); kinetics and mechanism
Authors: Basters J. , Groenenboom C. J. , van Bekkum H. , van Reijen L. L.
Published: September 2010

The homogeneous hydrogenation and deuteration with pentacyanocobaltate(II) of a series of substituted cis‐cinnamic acids have been investigated. During the hydrogenation partial isomerization to the corresponding trans‐isomers was observed. In the deuterations the labelling of the intermediate trans‐compounds ‐ as determined with PMR spectroscopy ‐ revealed that in cis‐cinnamic acids the first hydrogen transfer takes place at the α‐carbon atom. On the basis of effects of ortho‐substituents, isotope effects and deuterium labelling it is suggested that in trans‐cinnamic acids the initial hydrogen transfer takes place at the β‐carbon atom.
Molybdenum‐catalysed epoxidation of olefins with alkyl hydroperoxides I. Kinetic and product studies
Authors: Sheldon R. A.
Published: September 2010

In the homogeneous molybdenum‐catalysed epoxidation of olefins bytert‐alkyl hydroperoxides two competing processes, epoxidation and hydroperoxide decomposition, have been delineated.

Hydroperoxide decomposition involves free‐radical reactions initiated by electron‐transfer reactions of Mo(V) and Mo(VI) complexes with the hydroperoxide. The rates and products of hydroperoxide decomposition are dependent on the solvent and the presence or absence of an olefin.

The rate of epoxidation depends on the structure of the olefin and, after an initial period during which the rate changes, it becomes independent of the structure of the molybdenum compound originally added as the catalyst. The active catalyst in the epoxidation reaction is a molybdenum(VI) compound. The active epoxidizing agent is most likely a complex of molybdenum(VI) with the hydroperoxide, which transfers an oxygen atom to the olefin via a cyclic transition state analogous to that for the epoxidation of olefins with organic peracids.
Nouveaux oxamétallocycloalcanes (VII) Synthèse de (germa‐, sila‐, et stanna‐)dioxacycloalcanes et alcènes par insertion de dérivés carbonylés sur la liaison métal‐oxygène d'éthers cycliques organométalliques
Authors: Barrau J. , Massol M. , Mesnard D. , Satgé J.
Published: September 2010

The insertion reactions of carbonyl derivatives such as acetaldehyde, chloral, hexachloro‐ and hexafluoro‐acetone on the metal‐oxygen bond of alkoxy‐organometallic compounds have been studied in the case of numerous cyclic ethers containing silicon, germanium or tin atoms in the ring.

These reactions proceed by ring expansion leading to the formation of cyclic acetals: germaoxetanes yield 4‐germa‐1,3‐dioxanes, (sila‐, germa‐ or stanna‐) oxacyclopentanes give 1,3‐dioxacycloheptanes and (germa‐ or stanna‐) oxacyclopentenes lead to 1,3‐dioxacycloheptenes with the group IV element in position 4.

The mechanism of these insertion reactions is discussed according to the nature of carbonyl derivatives and metal heteroatom in the starting cyclic compounds, as well as catalytic and solvent effects.
The crystal and molecular structure of propenyl p‐tolyl sulfone
Authors: Klazinga A. H. , Vos Aafje
Published: September 2010

An X‐ray diffraction study of propenyl p‐tolyl sulfone has shown that the S‐CH = CH‐CH3 group has the trans configuration rather than the cis configuration assumed by Backer, Strating and Drenth.
Enolization and oxidation III. Ferrocene Catalyzed Autoxidation of 3‐Hydroxybutan‐2‐one in an Acidic Medium
Authors: Lubach J. , Drenth W.
Published: September 2010

The autoxidation of 3‐hydroxybutan‐2‐one is studied in acidic 50 vol. % aqueous ethanol. The reaction is catalyzed by ferrocene. The rate determining step of the ferrocene catalyzed reaction is the acid catalyzed enolization of the substrate. Subsequently, both the enol‐form of the substrate and ferrocene are oxidized by oxygen.
Force fields for the vinyl halides
Authors: Elst R. , Rogge W. , Oskam A.
Published: September 2010

Normal coordinate calculations of vinyl fluoride, chloride, bromide and iodide are reviewed. Modified Valence Force Fields are reported, by making use of published vibrational data of all deuterated isotopic species and observed Coriolis constants. The iterative least‐squares procedure used adjusts observed and calculated frequencies and second order Coriolis constants simultaneously, so we introduced a mutual dependency between the two vibrational species A′ and A″.

Our calculations suggest frequency reassignments for some isotopic molecules.
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (XXX) Reaction of chlorophenyl‐ and chlorodiphenyl‐pyrazines with potassium amide in liquid ammonia
Authors: Lont P. J. , van der Plas H. C.
Published: September 2010

While treatment of 2‐chloro‐3‐phenylpyrazine with potassium amide in liquid ammonia yields only 2‐amino‐3‐phenylpyrazine, from 2‐chloro‐6‐phenylpyrazine on the contrary two ring contraction products, 4(5)‐phenylimidazole and 2‐cyano‐4(5)‐phenylimidazole are obtained. From 2‐chloro‐5‐phenylpyrazine a mixture of 2‐amino‐5‐phenylpyrazine, 4(5)‐phenylimidazole as well as 2‐cyano‐4(5)‐phenylimidazole is formed.

In the diphenyl series it has been established that, whereas 2‐chloro‐3,5‐diphenylpyrazine gives only the corresponding 2‐aminopyrazine, 2‐chloro‐ 5,6‐diphenylpyrazine gives a mixture of the amino product and two ring contraction products: 4,5‐diphenylimidazole and 2‐cyano‐4,5‐diphenylimidazole.2‐Chloro‐3,6‐diphenylpyrazine was found to be relatively inactive towards potassium amide in liquid ammonia.

This divergent behaviour is explained by the high susceptibility of the positions 3 and 6 of the 2‐chloropyrazine for a nucleophilic attack as established by 14C‐ and 15N‐labelling studies which were made previously.
The reaction of 4‐chloroquinazoline with lithium piperidide in piperidine and potassium amide in liquid ammonia at −75°
Authors: de Valk J. , van der Plas H. C. , Jansen F. , Koudijs A.
Published: September 2010

Treatment of 4‐chloroquinazoline with lithium piperidide in piperidine at −75° yields a mixture of a stable open chain compound i.e. o‐(piperidinomethylene)iminobenzonitrile and the corresponding 4‐piperidino compound. When 4‐chloroquinazoline is aminated with potassium amide in liquid ammonia at −75° only 4‐aminoquinazoline is formed. By means of 15N‐labelling it has been shown that about 50% of the 4‐aminoquinazoline is formed via an ANRORC mechanism. The synthesis of 4‐chloro‐[3‐15N]quinazoline is described.
On the repetitive excess mixed anhydride method for the synthesis of peptides. Synthesis of the sequence 1‐10 of human growth hormone
Authors: Beyerman H.C. , de Leer E.W.B. , Floor J.
Published: September 2010

The synthesis of the fully protected N‐terminal decapeptide of human growth hormone, Boc‐Phe‐Pro‐Thr(Bzl)‐Ile‐Pro‐Leu‐Ser(Bzl)‐Arg(NO2)‐Leu‐Phe‐OMe (HGH 1‐10) by the repetitive excess mixed anhydride (REMA) method is described.

Starting from Phe‐OMe this sequence was synthesized in a stepwise manner in an overall yield of 59%. In the coupling of Boc‐Ile to Pro‐Leu‐Ser(Bzl)‐Arg‐(NO2)‐Leu‐Phe‐OMe the isobutoxycarbonyl derivative of the amino‐component was isolated. This problem of reaction on the undesirable side of the mixed anhydride in the couplings to proline‐peptides was circumvented by the coupling of dipeptides, viz. Boc‐Ile‐Pro and Boc‐Phe‐Pro. Also a larger peptide fragment, ZPhe‐Pro‐Thr‐Ile‐Pro (HGH 1‐5), was conveniently coupled to the C‐terminal pentapeptide. Synthesis of Boc‐Leu‐Ser(Bzl)‐Arg(NO2)‐Leu‐Phe‐OMe (HGH 6‐10) was performed with and without intermediate purification. It was found that the yield was higher when no purifications were applied.

HGH 6‐10 was compared with the corresponding peptide synthesized by the solid phase method. Both products were found to be identical with regard to melting point, optical rotation and chromatographic behaviour. The decapeptide, on deprotection, showed identical chromatographic behaviour with a product obtained by the solid phase method. The optical rotations showed a small difference; no significant racemization could be detected on digestion with L‐amino‐acid oxidase.
Kinetics and mechanism of primary cracking reactions in thermal high pressure hydrogenolysis of tetralin and indan. Part I
Authors: Penninger J.M.L. , Slotboom H.W.
Published: September 2010

Kinetics of the primary cracking reactions occurring in the high pressure thermal hydrogenolysis of 1, 2, 3, 4‐tetrahydronaphthalene (tetralin) and hydrindene (indan) were studied in a flow reactor at temperatures from 460° to 540°C, total pressures from 10 to 160 atm. and molar ratios of hydrogen‐to‐hydrocarbon from 2 to 100.

As primary cracking products from tetralin were identified n‐butylbenzene, styrene, ethylene, 1‐methylindan and o‐propyltoluene.

From indan were obtained n‐propylbenzene, toluene, ethylene, o‐ethyl‐toluene, o‐xylene and methane.

Chain mechanisms are proposed for the reactions leading to these primary products.

The theoretical rate equations derived from these are in good agreement with experimental results.
A novel type of catalysis of the [2 + 2] cycloaddition of cyclopropenes
Authors: Schipperijn A.J. , Lukas J.
Published: September 2010

In the presence of zeolites, cyclopropenes can cyclodimerize to give tricyclo‐[3.1.0.02,4]hexanes, isomerize to yield 1,3‐butadienes or polymerize. Which pathway is chosen depends on the structure of the cyclopropene and on the nature of the zeolite. This novel method for the cyclodimerization of cyclopropenes is superior to known procedures of preparing tricyclohexanes. It constitutes a unique example of a reaction being forced to proceed in a certain direction by spatial restriction of the reacting molecules.
Ketene formation from aliphatic ketones in a silent electrical discharge
Authors: van Drumpt J. D. , Mackor A.
Published: September 2010

The title reaction in the plasma of a silent electrical discharge at 40° is described. Acetone, ethyl methyl ketone, diethyl ketone and diisopropyl ketone all give rise to the formation of ketenes. From these ketones not only is the corresponding ketene formed, but the lower ketenes also, presumably by degradation of the higher ketenes in the plasma of the discharge. Acetic acid also gives rise to ketene formation. In contrast to the comparable thermal reactions, total ketene yields for the ketones are all of the same order of magnitude. With acetone and acetic acid the energy yields for ketene formation are better for the discharge than for the thermal reaction.
On the occurrence of the anrorc‐mechanism and a dimroth rearrangement in reactions of 4‐halogenopyrimidines with lithium isopropylamide
Authors: van Der Plas H. C. , Koudijs A.
Published: September 2010

In the reaction of 6‐bromo‐4‐phenylpyrimidine (1) with lithium isopropylamide at − 75°, the open‐chain product N′‐(2‐cyano‐1‐phenyl‐1‐vinylene)‐N‐isopropyl‐formamidine (5) is obtained. On standing, compound 5 isomerises slowly into 6‐imino‐4‐phenyl‐1‐isopropyl‐1,2‐dihydropyrimidine (6). On reaction of 1 with lithium isopropylamide at 20°, 4‐phenyl‐6‐isopropylaminopyrimidine (7) was formed. Evidence has been presented that 7 is formed by a complicated series of reactions involving an ANRORC‐mechanism (1 → 5 → 6) and a subsequent Dimroth rearrangement (6 → 9 → 10 → 7).
Vinyl orthoformates and vinyl acetals II: The reactions of alkenyl orthoesters and dialkenyloxyalkyl carboxylates with carboxylic acids
Authors: van Melick J. E. W. , Scheeren J. W. , Nivard R. J. F.
Published: September 2010

Several new alkenyl orthoesters have been synthesized by dehydrohalogenation of the corresponding β‐chloroalkyl orthoesters with various bases. With one equivalent of a carboxylic acid these compounds are converted into dialkenyloxyalkyl carboxylates in good yields. Dependent upon their composition, the latter products, give with another equivalent of a carboxylic acid either predominantly alkenyl esters and acylals, or alkenyl esters, carboxylic anhydrides and carbonyl derivatives. The synthetic applications have been investigated and a possible mechanism for these reactions is given.
A Reinvestigation of the extended Hückel calculation of cis‐2‐butene
Authors: Zeelen F. J.
Published: September 2010

A reinvestigation of the published extended Hückel calculation of cis‐2‐butene showed that this theory correctly predicts the conformation provided one allows for angle relaxation.
A synthesis of N‐phthaloyl amino acids and amino acid esters under mild conditions
Authors: Hoogwater D.A. , Reinhoudt D.N. , Lie T.S. , Gunneweg J.J. , Beyerman H.C.
Published: September 2010

The racemization‐free synthesis of N‐phthaloyl amino acids (Pht‐amino acids) from amino acid esters, by using o‐methoxycarbonylbenzoyl chloride in anhydrous media, is described. The N‐phthaloyl amino acids and esters from proteins were obtained in high yields.

Three N‐phthaloyl amino acids were synthesized for the first time: N‐Pht‐LTrp, N‐Pht‐S‐Bzl‐LCys and N‐Pht‐Nim‐Bzl‐LHis.

In the case of some sterically hindered amino acids, LIle and α‐amino‐isobutyric acid, the intermediate N‐(o‐methoxycarbonylbenzoyl) amino acid derivative could be isolated.
Photoaddition of aromatic ketones to some arylacetylenes; Formation of α,β‐unsaturated ketones and aldehydes
Authors: Polman H. , Mosterd A. , Bos H.J.T.
Published: September 2010

Photoaddition of aromatic ketones to 1‐alkyl‐2‐phenylacetylenes RCCC6H5 (R = CH3, C2H5) generally affords, via an oxete derivative, α,β‐unsaturated ketones Ar2CC(C6H5)COR in good or moderate yield.

With monosubstituted arylacetylenes Ar′CCH α,β‐unsaturated aldehydes Ar2CC(Ar′)CHO are formed.

In the reactions with 9‐xanthenone partial dehydrocyclization of the adducts occurs.
Synthesis of thiepen and thiocin derivatives via ring enlargement
Authors: Reinhoudt D.N. , Kouwenhoven C.G.
Published: September 2010

A general method has been developed for the synthesis of two novel classes of heterocyclic compounds, 2,3‐(or 2,7)‐dihydrothiepins and 2,3‐dihydro‐8H‐thiocins. It comprises the cycloaddition of enamine derivatives of tetrahydro‐thiophen‐3‐ones or 4‐thiacyclohexanone to activated acetylenes, e.g. dimethyl acetylenedicarboxylate, yielding bicyclic adducts, which upon thermal ring opening of the cyclobutene moiety afford the thiepin and thiocin derivatives.

The enamine group in these cyclic dienamines can be hydrolysed to give stabilized enols and/or their tautomeric ketones.

Peracid oxidation of the sulfur atom in the dihydrothiepins or dihydro‐2H‐thiocins produces the corresponding 1‐oxides or 1,1‐dioxides.
Synthesis of thiahydrindanones and thiadecalones by Dieckmann cyclization: The stereochemistry of thiolate anion addition to cyclohexenes
Authors: van Bruijnsvoort A. , de Waard E. R. , van Bruijnsvoort‐Meray J. L. , Huisman H. O.
Published: September 2010

The synthesis of trans‐3‐thiadecal‐1‐one (5) and cis‐3‐thiahydrindan‐1‐one (12) by Dieckmann cyclization (DC) is described. Anions of mercapto‐esters are shown to add to activated cyclohexenes in a trans diaxial fashion in kinetically controlled Michael additions (MA). An explanation is presented for the retro‐MA of cis‐1‐(2î‐ethoxycarbonylethylthio)‐2‐ethoxycarbonylcyclohexane (10) under DC‐conditions.
Pyrazoles and imidazoles as ligands. Part xviii: Neutral and anionic pyrazole coordinated to Cu(I) and Ag(I)
Authors: Okkersen H. , Groeneveld W. L. , Reedijk J.
Published: September 2010

A few compounds having the general formula M(L)+2 X− are reported, in which M(I) = Cu or Ag, X− = BF−4, NO−3, Cl−, Br−, and L stands for pyrazole, 3(5)‐methylpyrazole and 4‐nitropyrazole. The compounds are formed by reaction of MX and L in acidic medium. Infrared spectra of the compounds are consistent with linear cations ML+2 and uncoordinated anions.

Apart from the above compounds, a different class of compounds is formed in less protic media. These compounds are salt like and have the formula M+L−, with M+ = Cu+ and Ag+ and L = pyrazole, 4‐iodopyrazole, 4‐bromopyrazole, 4‐ethylpyrazole, 4‐nitropyrazole and 3(5)‐methylpyrazole.

Infrared spectra, mass spectra, X‐ray powder diagrams and solubility studies indicate that these compounds are at least trimeric and possibly polymeric with bridging pyrazolate anions between the metal ions.