bluuebunny/crossref_metadata_2025 huggingface dataset:
Mixed carboxylic acid anhydrides: I. Acetic‐formic anhydride
Authors: Stevens W. , van Es A.
Published: September 2010

The identity and purity of acetic‐formic anhydride prepared from ketene and formic acid have been established by means of N.M.R. and I.R. absorption data. On the basis of these data the presence of this mixed anhydride in the formylating reagent obtained from acetic anhydride and formic acid, could be proved and the composition of the reagent established. Indications were found, that on standing, acetic‐formic anhydride disproportionates into acetic anhydride and formic anhydride and that formic anhydride is also present in the formylating reagent.
Mollisin, a naturally occurring chlorine‐containing quinone: Part II,. The structure of mollisin
Authors: Overeem J. C. , van der Kerk G. J. M.
Published: September 2010

New evidence is presented which shows that the yellow pigment from the fungus Mollisia caesia, mollisin, formerly believed to be 8‐acetonyl‐2,3‐dichloro‐5‐hydroxy‐7‐(or 6)methyl‐naphthoquinone‐1,4 is in fact 8‐dichloro‐acetyl‐5‐hydroxy‐2,7‐dimethyl‐naphthoquinone‐1,4.
Cardiolipin and derivatives II.: Synthesis of diphosphatidylglycerol
Authors: de Haas G. H. , van Deenen L. L. M.
Published: September 2010

This paper describes the first synthesis of diphosphatidylglycerol.
N.M.R. studies of non‐bonded interactions in azabiphenyls
Authors: Murrell J. N. , Gil V. M. S. , van Duijneveldt F. B.
Published: September 2010

A study of the proton N.M.R. spectra of (aza)biphenyls at several temperatures and in various solvents has shown that the planarity of these molecules increases in the series biphenyl, 2‐phenylpyridine, 2‐phenylpyrimidine and 2,2′‐bipyridyl, the latter compound being mainly trans at room temperature. It follows that an ortho‐ortho CH… N interaction is less repulsive than a corresponding CH… CH interaction. Rapid rotation in molecules having one o‐nitrogen atom is found to persist at −65 °C.
The conformation of non‐aromatic ring compounds XXVI the absolute configuration of 2α,3β‐dibromo‐5α‐cholestane
Authors: van Heijkoop E. , Geise H. J. , Romers C.
Published: September 2010

The absolute configuration of 2α, 3β‐dibromo‐5α‐cholestane has been determined using the anomalous dispersion of X‐rays by the bromine atoms. The results agree with the generally accepted configuration of the steroids.
Enthalpies of solvation of alkali halides in formamide. II.: Evaluation of experimental ionic enthalpies of solvation
Authors: Somsen G.
Published: September 2010

From known lattice enthalpies and measured enthalpies of solution in formamide the enthalpies of solvation of 18 alkali halides in this solvent are calculated. A plot of the enthalpies of solvation of a series of alkali halides with one common cation against the reciprocal crystal radii of the anions is linear. Application of the extrapolation method results in a primary splitting of the total enthalpies of solvation of the salts into a set of experimental ionic enthalpies of solvation. As in water, the enthalpies of solvation in formamide for anions are larger than those for cations of the same size. The difference is smaller, however. The relation with absolute ionic enthalpies of solvation is discussed.
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (V): Conversion of some 2‐alkyl‐, 2‐aryl‐ and 2,5‐dialkyl‐4‐chloropyrimidines by potassium amide in liquid ammonia into 4‐alkyl derivatives of 2‐alkyl‐ or 2‐aryl‐s‐triazines
Authors: van der Plas H. C. , Haase B. , Zuurdeeg B. , Vollering M. C.
Published: September 2010

Reactions of 2‐methyl‐, 2‐ethyl‐, 2‐phenyl‐, 2,5‐ and 2,6‐dimethyl‐4‐chloropyrimidine with potassium amide in liquid ammonia have been investigated.

Together with aminations leading to the formation of 4‐amino compounds, conversions involving a ring transformation were found to occur. The latter process occurred in aminations of the three first‐mentioned substances, 2,4‐dimethyl‐, 2‐ethyl‐4‐methyl‐ and 4‐methyl‐2‐phenyl‐s‐triazine respectively being formed. Also from 4‐chloro‐2,5‐dimethylpyrimidine a s‐triazine derivative, 4‐ethyl‐2‐methyl‐s‐triazine, was obtained. The last‐mentioned reaction indicates that in the ring transformation pyrimidynes are not involved and that the 5‐methyl group and the 5‐carbon atom of the pyrimidine ring contribute to the formation of the ethyl group in the reaction product.

A mechanism for the ring transformation is proposed.
The system NbCl5Nb2O5. IV. The T‐x projection
Authors: Hart W. 'T‐x , Meyer G.
Published: September 2010

An investigation into the occurrence of compounds in the binary system NbCl5Nb2O5is described together with the determination of the phase‐compositions of the three‐phase equilibria SLG and SSG, as a function of temperature. Finally, the situation of part of the critical curve is established.
The diffusion potential between electrolyte solutions in different solvents: Some quantitative data about the contribution of the transport of solvent molecules through the boundary layer to the diffusion potential
Authors: Alfenaar M. , de Ligny C. L. , Remijnse A. G.
Published: September 2010

In the diffusion through the boundary layer between electrolyte solutions in different media, the transport of uncharged particles comes into play. The contribution of this transport to the diffusion potential is measured for alkali halide solutions in methanol‐water mixtures. Using Δμ0‐values of individual ions in methanol‐water mixtures, the total diffusion potentials are calculated.

It can be concluded that the diffusion potential between electrolyte solutions in different solvents depends mainly on the primary medium effect.
Complexes with ligands containing nitrile groups. Part II. Methyl cyanide complexes of some mono‐ and di‐valent metal chlorides with tin tetrachloride
Authors: Reedijk J. , Groeneveld W. L.
Published: September 2010

A number of complexes with the general formula M(CH3CN)n(anion)m, is reported. The anions are SnCl62− and (SnCl5 · CH3CN)−. The cations M are the monovalent ions: Li, Na, Cu, (C2H5)4N, and the divalent ions: Be, Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn. Most of the cations are completely solvated by the methyl cyanide in these complexes.

The compounds were synthesized by reaction of SnCl4 with the metal chlorides in methyl cyanide. In some cases this chloride‐ion transfer was studied spectrophotometrically and conductometrically. The ligand‐field splitting parameter (Dq) and Racah parameter (B) are calculated for some M(CH3CN)62+ ions.

Several complexes proved to be isomorphous from their X‐ray powder‐patterns. Information about the structure of the anions was obtained from far‐infrared and Raman spectra. The ternary phase‐diagram CoCl2‐SnCl4‐CH3CN is discussed.
The universal pH‐scale in methanol and methanol‐water mixtures
Authors: Alfenaar M. , de Ligny C. L.
Published: September 2010

The universal pH‐scale in methanol‐water mixtures and in methanol is defined, in terms of the pHst values of standard buffer solutions in these solvents as well as in terms of the pHst values of aqueous standard buffer solutions and the values of Ej(H2O) ‐ Ej(S)/0.05916. The accuracy is satisfactory. (0.01 to 0.12 pH‐units in 0‐90% methanol and 0.27 pH‐units in methanol).
Sulfur compounds in free radical reactions. Part III: Thermal decomposition of triphenylmethyl thionitrite
Authors: van Zwet H. , Kooyman E. C.
Published: September 2010

Triphenylmethyl thionitrite appears to be a convenient source of triphenylmethylthiyl radicals (Ph3CS•); the thermolysis Ph3CSNO → Ph3CS• + NO is reversible. The thiyl radicals may react with aralkyl hydrocarbons to form the corresponding thiol.
The photolysis of cyclopropanecarbaldehyde at 313 nm, a possible example of triplet‐triplet annihilation
Authors: Overwater J. J. I. , Cerfontain H.
Published: September 2010

Cyclopropanecarbaldehyde has been photolysed in the gas‐phase with light in the 313 nm region at temperatures from 50 to 190 °C and at various aldehyde pressures. The most important gaseous reaction products are carbon monoxide, propene and cyclopropane. The quantum yield of propene, which is practically independent of temperature, decreases with increasing aldehyde pressure. The quantum yield of cyclopropane increases with both temperature and aldehyde pressure but decreases with increasing intensity of the absorbed light.

It is proposed that propene is formed by intramolecular decomposition of singlet excited cyclopropanecarbaldehyde, whereas cyclopropane ultimately results from a radical decomposition of triplet cyclopropanecarbaldehyde.
Biologically active prostaglandins from some new odd‐numbered essential fatty acids
Authors: Beerthuis R. K. , Nugteren D. H. , Pabon H. J. J. , van Dorp D. A.
Published: September 2010

All‐cis 8,11,14‐octadecatrienoic‐(18:3 ω4), nonadecatrienoic‐(19:3 ω5), heneicosatrienoic‐(21:3 ω7), docosatrienoic‐(22:3 ω8) and 5,8,11,14‐nonadecatetraenoic‐(19:4 ω5) and heneicosatetraenoic‐(21:4 ω7) acid were synthesized. These fatty acids were used for a study of their enzymic conversion into homologues of prostaglandin E1 (PGE1) and E2 (PGE2) by a particulate fraction of sheep vesicular glands. Moreover, their essential fatty acid (EFA) activities in the rat were determined.

18:3 ω4 and 22:3 ω8 could not be converted into prostaglandin‐like materials; 19:3 ω5, 19:4 ω5, 21:3 ω7 and 21:4 ω7 yielded ω nor PGE1, ω nor PGE2, ω homo PGE1 and ω homo PGE2 respectively, the biological activities of which were comparable with those of PGE1 and PGE2, when tested on guinea pig ileum, rat blood pressure and ADP‐induced platelet aggregation. The conversion rates were compared with those of arachidonic acid (20:4 ω6) and dihomo‐y‐linolenic acid (20:3 ω6) and appeared to be, in decreasing order: 20:4 ω6 > 20:3 ω6 > 21:4 ω7 > 19:4 ω5 > 21:3 ω7 > 19:3 ω5.

Only the fatty acids that yielded biologically active prostaglandins showed considerable EFA‐activities; 18:3 ω4, 20:3 ω7 and 22:3 ω8 had no EFA‐activity. The ratios of the EFA‐activities of the fatty acids correlate roughly with the ratios of their conversion rates into prostaglandins.

The fatty acids obtained from the liver mitochondria of rats fed with the various fatty acids were analysed. A considerable incorporation was found for the C19 and C21 acids. The C19 and C21 trienoic acids were dehydrogenated for the greater part to their corresponding tetraenoic acids, whereas the C19 acids were partly chain‐lengthened and further dehydrogenated to 21:5 ω5. The conclusion is that all‐cis fatty acids with the structure:

CH3(CH2)n(CHCH‐CH2)4(CH2)2COOH, in which n = 3, 4 or 5, and those which can be converted by the rat into them, have EFA‐activity.
Transannular hemi‐acetal formation from 6‐hydroxycyclodecanone
Authors: Mijs W. J. , de Vries K. S. , Westra J. G. , Gaur H. A. Angad , Smidt J. , Vriend J.
Published: September 2010

The existence of a temperature and solvent dependent equilibrium between the oxo form (Ia) and the hemi‐acetal form (Ib) of 6‐hydroxycyclodecanone (I) has been proved by chemical methods and by infrared and nuclear magnetic resonance spectroscopy.
The structure of davanone a new sesquiterpene from davana: (Artemisia pallens, Wall.)
Authors: Sipma G. , van der Wal B.
Published: September 2010

Structure I, based on chemical and spectroscopic evidence, is proposed for a new sesquiterpenoid ketone, davanone, isolated from the essential oil of Artemisia pallens, Wall., known as davana oil.
Electronic and steric effects in the hydrogenation of alkyl aryl ketones on palladium
Authors: van Bekkum H. , Kieboom A.P.G. , van De Putte K.J.G.
Published: September 2010

The hydrogenation of some forty aromatic ketones to the corresponding alcohols has been studied in ethanol using carbon‐supported palladium as the catalyst. Zero order kinetics with respect to ketone is observed. For acetophenones electronic substituent effects may be expressed in terms of a Hammett‐Yukawa relationship with ρ = 0.7. 2‐Alkylacetophenones react very slowly. With alkyl phenyl ketones increase of size of the alkyl group causes increasing rate of hydrogenation. The adsorbed state is discussed on the basis of competition experiments.
The bromodecarboxylation of thiophenecarboxylic acids
Authors: Zwanenburg D. J. , Wynberg Hans
Published: September 2010

Bromodecarboxylation of the disodium salt of 3,4‐dimethylthiophene‐2,5‐dicarboxylate with bromine in water gave 2,5‐dibromo‐3,4‐dimethylthiophene. This bromodecarboxylation reaction, first mentioned by Melles and Backer (1953), has interesting synthetic aspects and a number of other examples are given.
Protonation of azo‐compounds. Part II: The structure of the conjugate acid of trans‐azobenzene
Authors: Hoefnagel M. A. , van Veen A. , Wepster B. M.
Published: September 2010

The basic strengths of trans‐azobenzene and its 2‐methyl and 2,2′‐dimethyl derivatives strongly favour the “classic” view that protonation of these compounds takes place with formation of an NH σ‐bond. This is further confirmed by the rates of oxidation by perbenzoic acid of these compounds and of the corresponding trans‐stilbenes.

A few remarks are made on the arguments which led to the assumption that the azo‐group acts as a “single basic center”.
Rearrangements of substituted propargyl vinyl sulfides: Formation of allenic dithioesters and their conversion into derivatives of 2H‐thiopyran and thiopene
Authors: Schuijl P. J. W. , Bos H. J. T. , Brandsma L.
Published: September 2010

Compounds of the general formula R1CH=C(SC2H5)S‐CH2C2≡CR2 (II) (with R1=H, alkyl or aryl and R2=H or CH3) prepared by metallation of dithioesters R1CH2C(=S)SC2H5 (I) with potassium amide in liquid ammonia and subsequent reaction with R2C≡CCH2Br, rearrange at elevated temperatures. The first product is the allenic dithioester CH2=C=C(R2)‐CH(R1)C(=S)SC2H5 (III), which can undergo cyclisation either to a 2 H‐thiopyran derivative (IV, see reaction scheme) or to a substituted thiophene (V, see scheme I). The thiopyran formation is strongly accelerated by triethylamine, whereas (traces of) acids favour the cyclisation to thiophenes.

Energies of activation for the conversion of II to III have been determined.
C17‐substituted 5‐ and 5(10)‐estrenes and their 7α‐methyl homologues
Authors: Bolt C. C. , de Jongh H. P. , Siegmann C. M. , van Vliet N. P. , Zeelen F. J.
Published: September 2010

17α‐Alkylated derivatives of 5‐estren‐17β‐ol and their 7α‐methyl homologues have been prepared (Chart I). The key step in these syntheses is the reduction of the 3β‐chloro‐5‐estrenes (IV) with lithium in liquid ammonia.

Similar derivatives of the 5(10)‐estrenes have been synthesised (Chart II). The preparation and the reduction of the dithio‐acetals VIII are discussed. 5(10)‐Estren‐17‐one has been obtained together with other double bond isomers by isomerisation of 4‐estren‐17‐one.
Complexes with ligands containing S = O. Part VIII. Metal solvates with the ligand 1,4‐dithiane monosulfoxide
Authors: Reedijk J. , Fleur A. H. M. , Groeneveld W. L.
Published: September 2010

The ligand properties of 1,4‐dithiane monosulfoxide (DTMSO) have been studied by preparing a number of coordination compounds of formula M(DTMSO)6(anion)n, and by investigating their structure and properties by means of physical measurements.

The ligand is shown, by means of infrared spectroscopy to coordinate via the oxygen lone pair electrons to the metal ions investigated.

Both infrared and ligand‐field spectra showed the presence of octahedral ions M(DTMSO)6n+ in the compounds M(DTMSO)6(ClO4)n and M(DTMSO)6(BF4)n. In the case of M = Cu2+ these ions are distorted from regular octahedral, as is shown by infrared spectroscopy and by paramagnetic resonance spectroscopy.

The ligand DTMSO has been placed in the spectrochemical and nephelauxetic series with respect to the metal ions Ni(II) and Co(II). The spectrochemical series appears to be DMSO < DTMSO < TOSO < PMSO, and the nephelauxetic series has the reversed order (DMSO = dimethyl sulfoxide, TOSO = 1,4‐thioxane sulfoxide, PMSO = pentamethylene sulfoxide).
Spectra of some tetrathiometallates and tetraselenometallates
Authors: Omloo W. P. F. A. M. , Jellinek F.
Published: September 2010

The electronic absorption spectra of (NH4)2MoS4 and K3VS4 have been studied and discussed in terms of Viste and Gray's MO scheme of tetrahedral tetroxometallate anions. Diffuse reflection spectra of the compounds Cu3MVX4 and Tl3MVX4 (MV = V, Nb, Ta; X = S, Se) show that the energies of the absorption edges and absorption maxima increase in the sequence MV = V → → Nb → Ta and decrease in the order X = O → S → Se. The infrared spectra of the sulfides were also investigated.
Chemistry of acetylenic ethers 94: Addition of carbonyl dichloride to 1‐alkynyl sulfides and 1‐alkynyl ethers
Authors: van den Bosch G. , Bos H. J. T. , Arens J. F.
Published: September 2010

1‐Alkynyl sulfides and 1‐alkynyl ethers of the type R‐CC‐Y‐R′ (R = H or alkyl, R′ = alkyl and Y = O or S) were converted into β‐alkyl‐thio‐ and β‐alkoxy‐β‐chloro‐acrylic chlorides R′Y‐CClCR‐CO‐Cl by addition of carbonyl dichloride (phosgene).

Thecis‐isomers are formed initially [Cl and (COCl)cis], but partial isomerization occurs during work‐up. Configurations were determined by comparison of the NMR data with those of several derivatives of acrylic acid.

Relative addition rates have been determined in competition experiments. The mechanism of the reaction is discussed.
The synthesis and spectra of some heterocyclic conjugated spiranes
Authors: Wynberg Hans , Heeres G. J. , Jordens P. , Sinnige H. J. M.
Published: September 2010

Four spiro[cyclopentabithiophene]fluorenes have been synthesized. A distinct bathochromic shift due to spiroconjugation is found in their UV spectra, as predicted by Simmons

H. E. Simmons and T. Fukunaga, J. Am. Chem. Soc. 89, 5208 (1967).

.
Réactivité des trialcoylalcoxy‐ et dialcoylalcoxychlorogermanes et de leurs isologues soufrés vis à vis des aldéhydes et des cétones
Authors: Dousse M. M. Gabriel , Satgé Jacques
Published: September 2010

Aldehydes and ketones add onto the germanium‐oxygen bond of triethylmethoxy‐ and diethylmethoxy‐chlorogermanes with formation of the corresponding germanium acetals, the stability, the mode of thermal decomposition and certain properties of which have been investigated.

The germanium acetals of hexafluoroacetone are stable. β‐Elimination reactions are observed from germanium acetals of chloral and hexachloroacetone. The decomposition of the germanium acetals of the aldehydes and ketones takes place, in the presence of H2PtCl6, to give the corresponding acetals of the starting carbonyl compounds and trialkylgermanium oxides.

Additions and decompositions of the same type are observed in the action of the aliphatic aldehydes on the trialkyl(alkylthio)‐ and dialkyl(alkylthio)‐chlorogermanes. Chloral gives a reversible insertion reaction, however, at 90°, besides the β‐elimination reaction, a chlorine‐methylthio exchange reaction is also observed with formation of tri(methylthio)acetaldehyde and triethyl‐germanium chloride.

The influence of the inductive effects of the substituents on the germanium or on the carbonyl group in the course of these reactions as well as the catalytic action of the chloroplatinic acid or of zinc chloride seem to confirm the addition mechanism considered.
Pyrazoles and imidazoles as ligands. Part IX: Some adducts formed between Cu(II) salts and substituted pyrazoles
Authors: Reedijk J. , Windhorst J.C.A. , van Ham N.H.M. , Groeneveld W.L.
Published: September 2010

A number of adducts of general formula Cu(PZ)x2+(anion)2− is reported. In this formula PZ stands for: pyrazole. N‐methyl pyrazole. 3(5)‐methylpyrazole. 3,5‐dimethylpyrazole. 4‐chloropyrazole, 4‐bromopyrazole and 4‐nitropyrazole; the anions are ClO4−, BF4−, NO3−. Br− and Cl−. The value of x varies from 2–4 for the several ligands and anions.

The compounds are synthesized from the hydrated Cu(II) salts and the stoichiometric amounts of pyrazoles in ethanol or acetone solutions, with the addition of triethyl orthoformate for dehydration.

The adducts were characterized and identified by chemical analyses, infrared spectra, ligand‐field spectra and paramagnetic measurements. In all compounds the Cu2+ ions were found to be in a six‐coordinate, distorted octahedral environment. In contrast with other divalent metal ions, solvates containing the unit Cu(PZ)62+ could not be prepared.
Complexes with ligands containing nitrile groups. Part XIII: Metal(II) solvates containing substituted benzonitriles as ligands
Authors: van Driel C.A.A. , Groeneveld W.L.
Published: September 2010

A number of solvates having the general formula M(R‐BN)n2+(anion−)2 is reported. The cations M are the divalent ions: Mg, Mn, Fe, Co, Ni, Cu, Zn and Cd. The substituted benzonitriles R‐BN are: 4‐Cl‐BN, 3‐Cl‐BN, 2‐Cl‐BN, 4‐CH3O‐BN, 2,6‐diCl‐BN, 3,4‐di(CH3O)‐BN and 2,5‐di(CH3)‐BN; n is usually 6 except for Cu2+ where n is found to be 6,5 or 4. One complex of Zn2+ is prepared where n is 4. The anions used are SbCl6−, FeCl4− and InCl4−.

The infrared nitrile absorptions are examined and compared with those of the free nitrile. Metal‐nitrogen vibrations are obtained from far‐infrared spectra. Ligand‐field spectra parameters have been calculated.
Optimization, mechanism, and kinetics of the hydrogenation of skipped polyynoic acids to all‐cis skipped polyenoic acids
Authors: Steenhoek A. , van Wijngaarden B. H. , Pabon H. J. J.
Published: September 2010

Hydrogenation of skipped polyynoic acids and esters over Lindlar's catalyst in the presence of quinoline proceeds with optimum results in light petroleum, ethyl acetate, or acetone at room temperature, yielding the corresponding all‐cis polyenoic compounds in purities of 90‐99%, depending on the number of triple bonds.

For hydrogenations of this type mechanistic schemes are presented, including the formation of ene‐ynoic intermediates. Using Langmuir adsorption and Hinshelwood kinetics, analogue computer simulation showed a simultaneous uptake of more than one H2 molecule to be an important step in the reaction route.

The formation of trans‐double bonds occurs only via isomerization of cis‐double bonds.
Nitrogen fixation by reduced transition metal complexes: I. ESR measurements on a nitrogen‐binding vanadium complex
Authors: Beelen T. P. M. , van Erk W.
Published: September 2010

Molecular nitrogen has been bonded on vanadium trichloride, after reduction with lithium naphthalide. During these reduction and fixation reactions several ESR‐signals appeared. By measurements of signal intensities in the presence and absence of N2it was shown that these signals did not correspond with a vanadium‐nitrogen complex. They do indicate, however, the degree of reduction of the system and therefore provide information on the state of reduction of the complex (not ESR‐active in itself) that binds N2.
Chemistry of small ring compounds. Part 16: Kinetics and mechanism of the isomerization of some 1,1‐cyclopropanedicarboxylic acids in water and in aqueous sulfuric acid
Authors: Bus J. , Steinberg H. , de Boer Th. J.
Published: September 2010

The kinetics of the isomerization of 1,1‐cyclopropanedicarboxylic acid 1a to αcarboxy‐γ‐butyrolactone 3a in D2O and in aqueous D2SO4 (up to 56%) has been studied at temperatures up to 160°C.

The pseudo first‐order reaction is progressively accelerated by increasing sulfuric acid concentrations and according to Bunnett's w, w* and ψ‐values, the rate‐limiting step is probably the nucleophilic attack of water on a cyclopropyl ring carbon atom of the protonated substrate.

2‐Methyl‐1,1‐cyclopropanedicarboxylic acid 1b and 2,2‐dimethyl‐ 1,1‐cyclopropanedicarboxylic acid 1c isomerize faster than 1a by a factor of 31 and 80,000 respectively. The tremendous, rate‐enhancement of 1c can be explained by a rate‐limiting dissociation of a ring carbon‐carbon bond of the protonated substrate (SN1‐reaction).
Epoxidation of olefins by alkylperoxy radicals
Authors: Koelewijn P.
Published: September 2010

We have studied the reactions of alkylperoxy radicals with olefins in an inert solvent and atmosphere. The peroxy radicals react by addition to the double bond, mainly leading to epoxide formation, and by abstraction of allylic hydrogen, followed by termination between allyl and peroxy radicals. Relative and absolute rate constants at 120°C have been determined of the reactions of tert‐butylperoxy radicals with 2,3‐dimethyl‐2‐butene, 1‐hexene, α‐methylstyrene, propene, 3,3‐dimethyl‐1‐butene and styrene, and of α‐cumylperoxy radicals with 3,3‐dimethyl‐1‐butene.

We have found that for olefins having allylic hydrogen the abstraction/addition ratio determines the efficiency as well as the rate of epoxide formation, whereas substantial epoxide formation from olefins lacking easily abstractable hydrogen atoms can be expected only if the double bond is sufficiently reactive to suppress the reactions between the peroxy radicals.
Reactions of hydroxycarbonium ions in strong acids VI: Interconversion of trimethyltetrahydrofuryl ions via dicarbonium ions. Relative acidities of superacids
Authors: Brouwer D. M. , van Doorn J. A.
Published: September 2010

The rearrangement of 5‐ethyl‐2‐methyltetrahydrofuryl ion (2) to the 2,5,5‐trimethyltetrahydrofuryl ion (4) is proceeded by a much more rapid equilibration of 2 with the 2,4,5‐trimethyl isomers (3, cis and trans). These reactions are both acid catalysed and only take place in superacids (HF‐SbF5 and FSO3H‐SbF5). They involve skeleton rearrangements in intermediate dications (C,O‐diprotonated alkenones), the most stable one of which has been observed directly in 1:1 HF‐SbF5.

From the rates of the above and other, similar reactions the relative acidities of 1:1 HF‐SbF5, 9:1 HF‐SbF5, 1:1 FSO3H‐SbF5 and 5:1 FSO3H‐SbF5 have been estimated as > 500:1:10−1:10−5.

From the fact that 2 isomerizes much faster to 3 than to 4 it is concluded that in branching rearrangements of alkylcarbonium ions (e.g. linear to mono‐branched ions) the ring opening of the intermediate protonated 1,2‐dialkyl‐cyclopropane to the branched structure goes first to a secondary branched ion as a distinct intermediate.
Ring transformations in reactions of heterocyclic halogeno compounds with nucleophiles (XXV): On the mechanism of the conversion of chloropyrazine into aminopyrazine and of 2‐chloroquinoxaline into 2‐aminoquinoxaline with potassium amide in liquid ammonia
Authors: Lont P. J. , van der Plas H. C. , Verbeek A. J.
Published: September 2010

It has been found that 2‐chloropyrazine, containing an excess of 15N in position 1, by treatment with potassium amide in liquid ammonia at −65° yields 2‐aminopyrazine, in which the exocyclic nitrogen contains all the excess of 15N. An A(ddition)‐N(ucleophilic)‐R(ing)‐O(pening)‐R(ing)‐C(losure) mechanism is proposed. The corresponding animation of 2‐chloro[1(4)‐15N]quinoxaline at −33° leads to 2‐amino[1(4)‐15N]quinoxaline. In the last‐mentioned conversion an A(ddition)‐E(limination) mechanism is operative.
Reactions of hydroxycarbonium ions in strong acids. VII: Rearrangement of the 2,5,5‐trimethyldihydrofuryl ion, a heteroaromatic carbonium‐ion rearrangement
Authors: Brouwer D. M. , van Doorn J. A. , Kiffen A. A.
Published: September 2010

The rearrangement of 2,5,5‐ to 2,4,5‐trimethyldihydrofuryl ion, a heteroaromatic rearrangement via 1,2‐methyl and hydride shifts, is reported. The half‐life of the reaction is about 25 minutes at 100°.
Reduction and reductive alkylation of cycloheptatriene with alkali metals in liquid ammonia
Authors: Dirkzwager H. , Nieuwstad Th. J. , van Wijk A. M. , van Bekkum H.
Published: September 2010

When treated with alkali metals in liquid ammonia at −70° cycloheptatriene adopts two electrons and a proton yielding the cycloheptadienyl anion. Protonation of this anion yields 1,3‐ and 1,4‐cycloheptadiene in a ratio which depends rather strongly on the proton donor used. Decreasing acid strength of the proton donor favours 1,3‐cycloheptadiene formation. The selectivity of protonation also depends on the alkali metal used and on the concentration. At −33° ammonia protonates the cycloheptadienyl anion yielding 1,3‐cycloheptadiene. This enables one step reduction of cycloheptatriene to cycloheptene. Reduction of 7‐deuterocycloheptatriene shows the first proton addition to cycloheptatriene to be irreversible.

Alkylation of the cycloheptadienyl anion yields mixtures of 3‐alkyl‐1,4‐cycloheptadiene and 5‐alkyl‐1,3‐cycloheptadiene in which the former compound invariably predominates.
The selective monobromination of methane with mixtures of bromine and chlorine
Authors: van Drumpt J. D.
Published: September 2010

The reaction between methane and mixtures of bromine and chlorine was investigated.

Maximum conversions of bromine into methyl bromide of 63% were obtained; this yield can be improved by further increasing the methane: halogen ratio.

When ethane was used instead of methane, higher yields (up to 75%) and a higher selectivity towards monobromination were found.

The results strongly suggest a branched free radical chain reaction. The rate determining step is the attack of a chlorine radical on the hydrocarbon.

These conclusions are supported by approximate calculations, based upon the proposed reaction mechanism.
Aromatic lead(IV) compounds IV The plumbylation of halogen‐ and alkyl‐substituted aromatic ethers
Authors: de Vos D. , Boschman F. E. H. , Wolters J. , van der Gen A.
Published: September 2010

The preparation and some physical properties of aryllead triacetates in which the nucleus bears an alkoxy and a halogen or alkyl substituent, are reported.
Preparation of 5‐cyano‐2H‐thiopyrans and 4‐cyano‐2‐methylthiophenes by thermal rearrangement of the adducts from 2‐propynethiol and cyanoalkynes
Authors: van Der Welle R. A. , Brandsma L.
Published: September 2010

5‐Cyano‐2H‐thiopyran and a number of derivatives have been obtained in fair to good yields by heating compounds with the system CCCSCCCN in silicon oil; 4‐cyano‐2‐methylthiophenes are formed by heating these systems in dimethylsulfoxide in the presence of diisopropylamine. The starting systems were prepared by nucleophilic addition of 2‐propynethiol, HCCCH2SH, to cyanoalkynes RCCCN (R  H or alkyl).
Polyisocyanides II. Kinetics and mechanism of the polymerization
Authors: Nolte R. J. M. , Drenth W.
Published: September 2010

The kinetics of polymerization of various isocyanides by nickel(II) compounds has been studied. The data suggest that reaction occurs by means of successive isocyanide insertions at a positive nickel centre.
Mechanism of the antioxidant action of dialkyl sulfoxides II. Aspects of the antioxidant and pro‐oxidant actions of sulfoxides
Authors: Koelewijn P. , Berger H.
Published: September 2010

This paper analyses several complicating factors which can play a role in the inhibition of autoxidation by dialkyl sulfoxides, the uncomplicated case having been dealt with in the first paper1. It was found that in those cases where the autoxidation proceeds via tertiary peroxy radicals, sulfoxides yielding tertiary (or, possibly, also secondary) alkylsulfenic acids show poor antioxidant activity. This is attributed to the generation of radicals from the sulfinic acid perester formed by the reaction of peroxy radicals with the sulfinic radicals produced in the inhibition reaction.

A type of inhibition of autoxidation which does not involve radical scavenging arises from the ionic decomposition of hydroperoxides by strong acids formed from sulfoxides; this type of inhibition is most effective with those sulfoxides which are also active as inhibitors via the formation of sulfenic acid.

Sulfoxides also display a pro‐oxidant action, which is explained as a catalysis of the radical decomposition of hydroperoxides via the formation of a compound or complex from hydroperoxide and sulfoxide.
Reaction of 2‐halogeno‐4‐phenylpyrimidines with potassium amide in liquid ammonia. On the possible occurrence of two SN(ANRORC)‐mechanisms
Authors: Kroon A. P. , van der Plas H. C.
Published: September 2010

On amination of 2‐X‐4‐phenylpyrimidine (X=F, Cl, 1) with potassium amide in liquid ammonia at −75°. 2‐amino‐4‐phenylpyrimidine is obtained as main product, together with some 3‐amino‐3‐phenylacrylonitrile. It was proved using 2‐halogeno‐4‐phenyl‐[1,3‐15N]‐pyrimidines that the displacement reaction occurs for the greater partviaan SN(ANRORC)‐mechanism (82% for X=F, 88% for X=Cl and 73% for X=1). It was further found that the 3‐amino‐3‐phenylacrylonitrile, obtained from the15N‐labelled pyrimidines.does not contain15N. This very unexpected result is discussed.
The chemistry of small ring compounds. Part 27. Heterocyclic condensation products from cyclopropanone and methylamine
Authors: van Tilborg W. J. M. , Steinberg H. , de Boer Th. J.
Published: September 2010

The adduct 2 of methylamine with two molecules of cyclopropanone gives, on mild heating, a variety of six‐ and eight‐membered heterocycles (with hetero‐atoms NNN, NON, ONO, NONO or ONOO) and three or four unruptured (spiro‐)cyclopropyl groups attached to the ring. The cyclisation mechanism involves in all cases an initial rapid dimerisation of 2.

The aniline‐cyclopropanone adduct 10 on heating gives only the related six‐membered cyclo‐condensation products.
Nucleophilic additions on sulfonyl cyanides. Formation of C‐(arylsulfonyl)‐ and C‐(alkylsulfonyl)formamidrazones and their conversion to 1,2,4‐triazoles
Authors: Jagt J.C. , van Leusen A.M.
Published: September 2010

C‐Sulfonylformamidrazones are formed as isolable adducts from sulfonyl cyanides and the α‐effect nucleophiles hydrazine and phenylhydrazine. The adducts react with triethyl orthoformate or orthoacetate to give 1,2,4‐triazoles.
Base‐catalysed cyclisation of trans‐enyne alcohols to derivatives of furan
Authors: Schreurs P.H.M. , Galesloot W.G. , Brandsma L.
Published: September 2010

trans‐Enyne alcohols of the type R1C≡CCHCHCR2R3OH (R2 and R3 = H or alkyl) undergo cyclisation to substituted furans or dihydrofurans with potassium tert‐butoxide in dimethyl sulfoxide at 100° (if R1 = H) or at 25° (if R1 = CH3S or Ph).
Electrophilic alkylation of thiocamphorS‐oxide
Authors: Veenstra G.E. , Zwanenburg B.
Published: September 2010

Treatment of thiocamphorS‐oxide2with thallium(I) ethoxide gives a thallium(I) vinyl‐sulfenate which alkylates at sulfur with the alkyl halides CH3I, C6H5CH2Br, CH2CHCH2Br, EtOOCCH2Br, NCCH2Cl, CH3COCH2Cl andp‐BrC6H4COCH2Br to the α,β‐unsaturated sulfoxides3. These products were converted into the corresponding sulfones which were prepared by an alternative route from thiocamphor by treatment with LiN(iPr)2,S‐alkylation to vinyl sulfides5and subsequent oxidation.
Hexakis(imidazole)nickel(II) formate, an example of a coordination compound containing uncoordinated formate ions
Authors: Jansen J.C. , Reedijk J.
Published: September 2010

The preparation and characterisation of hexakis(imidazole)nickel(II) formate is described. The compound is unique in the sense that it contains formate anions, that are not coordinated to the metal ion. The crystal lattice of this compound ‐ and the isomorphous CoIIand CdIIcompounds ‐ seems to be stabilized by very strong hydrogen bond interactions between the N‐H group of imidazole and the formate anion.

A warning is made against the use of the common dehydrating agent triethyl orthoformate, in the presence of ligands that contain protic groups.
13C NMR study of the complex formation of sorbitol (glucitol) with multivalent cations in aqueous solution using lanthanide(III) nitrates as shift reagents
Authors: Kieboom A. P. G. , Sinnema A. , van der Toorn J. M. , van Bekkum H.
Published: September 2010

Complexation of sorbitol (glucitol) in aqueous solutions with the lanthanide ions LaIII, PrIII, EuIII and YbIII, as model systems for the complexation with the isosteric CaII, was studied by 13C NMR spectroscopy. Ytterbium(III) nitrate proved to be the reagent of choice, in effectiveness and in linearity vs concentration of the induced upfield shift. Tridentate complexation of YbIII with O‐2, O‐3 and O‐4 was established and the conformation of the sorbitol‐YbIII complex in water was found to be the same as that of the sorbitol‐PrIII complex, as inferred from 1H NMR spectra.

Off‐resonance decoupling and the isotope effects observed in sorbitol‐1‐d and sorbitol‐5‐d, allowed the complete, reliable assignment of the 13C NMR spectrum of sorbitol. Assignments in the literature proved to be incorrect.
The “overirradiation products” of previtamin D and tachysterol: Toxisterols
Authors: Boomsma F. , Jacobs H. J. C. , Havinga E. , van der Gen A.
Published: September 2010

The structures of the “toxisterols”, products formed upon prolonged irradiation of previtamin D and its photoisomers, have been investigated. Irradiations (λ > 300 nm) were carried out both in diethyl ether and in alcoholic solvents under conditions where the thermal isomerization to vitamin D is suppressed. From the irradiation mixtures a total of thirteen toxisterols have been isolated. On the basis of structural similarities they have been classified into six categories. In ethereal solution two bicyclo[3.1.0]hexeno compounds (toxisterols C) constitute the major fraction of the irradiation mixture; in addition, a partly deconjugated 9,10‐seco‐triene (toxisterol D1), two C‐8 spiro compounds (toxisterols A) and a cyclobuteno compound (toxisterol E1) are found. In alcoholic solutions about half of the irradiation mixture consists of three alcohol addition products (toxisterols B) ‐ which, upon chromatography, in part give rise to two conjugated 9,10‐seco‐trienes (toxisterols D2 and D3) ‐ and a reduction product (toxisterol R1); furthermore, three toxisterols A, two toxisterols C and toxisterol D1 are found. Toxisterols A, B and R represent novel types of products in hexatriene photochemistry.
On the closure of the 4,5‐oxygen bridge in morphinans 1H and 13C NMR spectroscopy of brominated intermediates. (Chemistry of opium alkaloids, Part IX)
Authors: Olieman C. , Maat L. , Beyerman H. C.
Published: September 2010

1H and 13C Nuclear magnetic resonance spectra of brominated dihydrothebainones, needed for the closure of the oxygen bridge of morphinans to form morphine derivatives, were studied. Bromination of (‐)‐dihydrothebainone (1) yielded successively 1‐bromo‐, 1,7α‐dibromo‐, and 1,5β,7α‐tribromo‐dihydrothebainone (2,3,4). 1‐Bromo‐O4‐methyldihydrothebainone (12) gave, after bromination, a stable crystalline l,5β,7α‐tribromo derivative (15). A 5β,7α‐dibromo derivative (9) was formed also starting with l‐methyldihydrothebainone (7).

Closure of the oxygen bridge in 1,5β,7α‐tribromodihydrothebainone (4) in boiling ethanol, yields an equilibrium mixture of 1,7β‐ and 1,7β‐dibromodihydrothebainone (5:6, ∼ 35 : 65). 5β,7α‐Dibromo‐l‐methyldihydrothebainone (9) gave the same result.

13C NMR spectra of the model compounds cyclohexanone, 2‐bromo‐, 2,2‐dibromo‐, cis‐ and trans‐2,6‐dibromo‐cyclohexanone were studied.
A convenient and general synthesis of 1,2‐dimethylenecycloalkanes
Authors: van Straten J. W. , van Norden J. J. , van Schaik T. A. M. , Franke G. Th. , de Wolf W. H. , Bickelhaupt F.
Published: September 2010

Cycloalkanones can be converted to the corresponding 1,2‐dimethylenecycloalkanes (1), in 10‐50% overall yield by a four‐step sequence involving Mannich condensation, Wittig reaction and Hofmann degradation. The conformation of 1 is briefly discussed.
Poly(iminomethylenes). 7. Synthesis of diphenylphosphine‐substituted poly[(l‐phenylethyl)iminomethylene]
Authors: Naaktgeboren A. J. , Nolte R. J. M. , Drenth W.
Published: September 2010

Polymer‐anchored phosphine functions were obtained in two ways: by diphenylphosphination of poly[[l‐(4‐bromophenyl)ethyl]iminomethylene] and by polymerization of l‐[4(diphenylphosphino)phenyl]‐l‐isocyanoethane. The synthesis of the monomers and polymers is described.
Poly(iminomethylenes). 10. Esterolytic catalysis by poly(carbylhistidine) and poly(carbylhistamine)
Authors: van der Eijk J.M. , Gusdorf Ch. F. , Nolte R.J.M. , Drenth W.
Published: September 2010

The catalytic activities in the hydrolysis of 4‐nitro‐ and 2,4‐dinitrophenyl acetate were determined for a polymer of 3‐(4‐imidazolyl)‐2‐isocyanopropanoic acid (1a) and of 2‐(4‐imidazolyl)‐1‐isocyanoethane (1b). A detailed kinetic analysis has been performed. The reaction starts with acylation of the imidazole groups followed by deacylation. With excess of substrate the second step is rate‐determining and the system shows burst kinetics behaviour. The rate of acylation of 1a can be analyzed by a two term equation; the major term involves the COOH groups. A transition state is proposed in which COOH stabilizes the negative charge developing on carbonyl oxygen. This system is approximately 400 times more active than e.g. histidine. The data for 1b reveal that the polymer imidazole groups are approximately six times more active than e.g. the imidazole group of histamine. This phenomenon is ascribed to a cooperative effect of the polymer imidazoles.

The deacylation is general base catalysed. Its rate constants are almost equal to those of acetylimidazole.

For comparison, the hydrolysis of the charged substrates 4‐acetoxy‐3‐nitrobenzoic acid anion and 3‐acetoxy‐N,N,N‐trimethylanilinium iodide by 1a and 1b has been included.
Synthesis of 1‐isocyano‐1‐tosyl‐1‐alkenes and their use in the preparation of imidazoles
Authors: van Leusen Albert M. , Schaart Fokko J. , van Leusen Daan
Published: September 2010

1‐Isocyano‐1‐tosyl‐1‐alkenes (1) are useful new synthons. They are obtained by dehydration of the corresponding N‐(1‐tosyl‐1‐alkenyl)formamides (4), which are reaction products of tosylmethyl isocyanide (2) and aldehydes or ketones. 1‐Isocyano‐1‐tosyl‐1‐alkenes 1 react smoothly with primary aliphatic amines (or ammonia) to give 1,5‐disubstituted (or 5‐monosubstituted) imidazoles (7) in high yields.
Photocatalysis IV. Preparation and characterization of a stable copper(I) triflate·trans‐cycloheptene complex
Authors: Evers J. Th. M. , Mackor A.
Published: September 2010

When copper(I) triflate·cis‐cycloheptene is irradiated at 254 nm in n‐hexane solution, cis → trans‐isomerization occurs and the stable complex copper (I) triflate·trans‐cycloheptene precipitates. This complex has been isolated, purified and characterized by elemental analysis and by its 1H and 13C NMR, Raman and UV spectra.
Stereoselective synthesis of (+)‐pilocarpine, an imidazole alkaloid used in ophthalmology (Imidazole Chemistry, Part VII)
Authors: Noordam A. , Maat L. , Beyerman H. C.
Published: September 2010

The synthesis of a mixture of (+)‐pilocarpine and (+)‐isopilocarpine from L‐histidine is described. Their separation is known.
Synthesis of fragments of human β‐lipotropin, βh‐LPH. Part II. The synthesis of βh‐LPH‐(61‐91), βh‐endorphin
Authors: van Nispen J. W. , Bijl W. A. A. J. , Greven H. M.
Published: September 2010

The classical fragment condensation approach was used to synthesize the hentriacontapeptide human β‐endorphin [βh‐LPH‐(61‐91)].
Helical configuration of poly(tert‐butyliminomethylene). Complete resolution and maximum optical rotation
Authors: van Beijnen A. J. M. , Nolte R. J. M. , Drenth W.
Published: September 2010

By repeated chromatography over optically active poly(sec‐butyliminomethylene) on glass beads complete resolution of poly(tert‐butyliminomethylene) was obtained. The specific rotation increases with molecular weight up to [α]20578 = 56 ± 2° at approximately 20 repeating units.
Gold‐phosphine cluster compounds: The reactions of [Au9L8]3+ (L = PPh3) with L, SCN− and Cl− to [Au8L8]2+ (Au11L8(SCN)2]+ and [Au11L8Cl2]+
Authors: Vollenbroek F. A. , Bour J. J. , van der Veden J. W. A.
Published: September 2010

[Au9L8]3+ reacts with L to give [Au8L8]2+ via the intermediate [Au8L7]2+. The reaction of [Au9L8]3+ with SCN− and Cl− results in the formation of [Au11L8(SCN2]+ and [Au11L8Cl2]+, respectively. [Au8L8]2+ acts as an intermediate in this conversion of Au9 into Au11. The 2+ charge on the [Au8L8]2+ cluster and its diamagnetic nature can be rationalized by a simple Hückel MO calculation.
Coordination compounds of platinum(II) with 2‐methylimidazole and 1,2‐dimethylimidazole
Authors: Marcelis A. T. M. , van Kralingen C. G. , Opschoor J. , Reedijk J.
Published: September 2010

The synthesis and characterization of new Pt(II) coordination compounds with the nitrogen‐donor ligands 2‐methylimidazole (2MIz) and 1,2‐dimethylimidazole (DMIz) are described. The compounds concerncis‐Pt(2MIz), X2,cis‐Pt(DMIz)2X2, [Pt(2MIz)4]X2(H2O)n, [Pt(DMIz)4]X2,trans‐Pt(DMIz)2X2where X = Cl, Br or I and n = 0 or 2, andtrans‐Pt(2MIz)2I2. Despite several attempts no other puretrans‐platinum compounds of 2MIz could be obtained.

The new compounds were characterized by chemical analyses, X‐ray powder diffraction photographs, vibrational spectroscopy (IR and far‐IR) and proton nuclear magnetic resonance.

In all cases the metal(II) ions are square‐planar coordinated.
The oxidation of hexahelicenes. Synthesis of hexahelicene‐5,6‐quinone
Authors: Diesveld J. W. , Borkent J. H. , Laarhoven W. H.
Published: September 2010

The remarkable ease with which 1,3,14,16‐tetramethylhexahelicene can be oxidised has to be ascribed to the electronic effect of multiple methyl substitution and not to disturbance of the helical conformation, as might be concluded from the polarographic oxidation potentials of hexahelicene and some of its methyl derivatives. Oxidation of hexahelicene with chromic acid in acetic acid gives hexahelicene‐5,6‐quinone in 70% yield. Its structure was proven by spectroscopic methods.
The synthesis of aldehydes by means of a modified Rosenmund reduction of acid chlorides
Authors: Peters J. A. , van Bekkum H.
Published: September 2010

Aliphatic as well as aromatic acid chlorides are reduced smoothly into aldehydes at room temperature and atmospheric pressure by hydrogenation, using palladium on carbon as the catalyst, acetone or ethyl acetate as solvent and ethyldiisopropylamine as hydrogen chloride acceptor. The reaction has a high selectivity and under the conditions used, no over‐reduction nor reduction of aromatic rings, of nitro and chloro substituents in benzoyl chlorides, or double bonds in cinnamoyl chlorides, was observed. The selectivity is probably the result of a combination of factors, such as selective adsorption of the acid chloride on the catalyst (with respect to the aldehyde) and partial poisoning of the catalyst surface by co‐adsorption of ethyldiisopropylamine and its hydrochloride.
Reaction of spiro[1,3‐benzodioxole‐benzothiazines] with hydroxylamine and active methylene compounds
Authors: Latif N. , Zeid I. F. , Mishriky N. , Assad F. M.
Published: September 2010

The reactivity of the title spiranes (1) towards cleavage by different nucleophiles in ethanolic solutions has been investigated. The spiranes are cleaved by ethyl p‐aminobenzoate to give 2‐aryl‐3‐(4‐methoxycarbonylphenyl)‐3H‐quinazoline‐4‐thiones (2b–d) together with tetrachlorocatechol, in a manner similar to the reaction with anilines and hydrazines. However, cleavage with hydroxylamine in ethanol affords ethyl 2‐(thioaroylamino)benzoates (4) in addition to the expected 2‐aryl‐3‐hydroxy‐3H‐quinazoline‐4‐thiones (2e‐f).

In contrast to the situation found with amines and hydrazines, the spiranes give 4‐(dicyanomethylene)‐and 4‐[cyano(ethoxycarbonyl)methylene]‐2‐aryl‐3,1‐benzothiazines (5) along with the 2‐(thioaroylamino)benzoates (4) when reacted with malononitrile and with ethyl cyanoacetate. In all cases, tetrachlorocatechol is produced. Reaction pathways are discussed.
Conformational studies on helicenes VII. Synthesis and conformation of 5,6‐dihydrohexahelicene
Authors: Borkent J. H. , Diesveld J. W. , Laarhoven W. H.
Published: September 2010

Irradiation of 2,7‐distyrylnaphthalene or 2‐styrylbenzo[c]phenanthrene under completely oxygen‐free conditions gives rise to the formation of 5,6‐dihydrohexahelicene (2) as a consequence of H‐shifts in the primary formed cyclization product. The conformation of2was analysed by NMR spectroscopy. From the chemical shifts of the aromatic protons, the coupling constants of the saturated moiety and the temperature independence of the spectrum it could be concluded that2occurs in one conformation, in which the axial proton at C(5) is directed towards the opposite ring. The resemblance of the spectra of2and l‐phenylbenzo[c]phenanthrene affirms that this conformation is the less hindered one.