bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectres et conformations, en solution, des complexes de transfert de charge entre les stilbènes para‐substitués et le tétracyanoéthylène
Authors: Albert J. L. , Gamier F. , Dubois J. E.
Published: September 2010

Solutions of tétracyanoéthylène and nine mono‐ and di‐para‐substituted stilbene derivatives magnified image (XH, CH3, MeO, Cl, Br, NO2) show two charge transfer bands in the UV visible spectrum range, associated with two molecular complexes I and II. The position of the first band around 17000 cm−1 is highly dependent on the substituent, whereas the position of the second band is almost constant about 26000 cm−1 (except for the complex of 4,4′‐dimethoxystilbene).

These two bands are assigned to the transitions from the two highest occupied molecular orbitals of the donors, calculated by the method of Huckel. Taking account of the symmetries of the stilbènes and tétracyanoéthylène molecular orbitals, two most probable configurations are proposed for these molecular complexes, I and II, and one in particular for the 4,4′‐dimethoxy derivative. The determination of the differences in formation enthalpy, ΔΔH, for these two complexes I and II, experimentally confirms the particular behaviour of the 4,4′‐dimethoxystilbene.
Studies on polypeptides XV Synthesis of L‐ and D‐homohistidine
Authors: Bloemhoff W. , Kerling K. E. T.
Published: September 2010

Optical resolution of DL‐homohistidine could be effected by fractional crystallization of the diastereomeric hydrogen tartrates. Starting from L‐glutamic acid, the direct synthesis of L‐homohistidine was accomplished through a ten‐stage synthesis requiring the isolation of only six intermediates.
Proton NMR spectra of di‐iodobis(N,N‐di‐n‐butyldithiocarbamato)‐platinum
Authors: Willemse J. , Pijpers F. W. , Backus J. J. M.
Published: September 2010

Proton NMR spectra of cis‐Pt(Bu2dtc)2I2 show, between −100 and + 100°C, two triplets of the α‐protons, even at 220 MHz no further splitting of the triplets could be observed. At about 100°C both triplets coalesce to a single one due to an intramolecular process (ΔH≠ = 7.2 kcal/mole and ΔS≠ = −37 eu). The proton NMR spectrum of cis‐Pt(MeBzdtc)2I2 shows two signals for both the methyl and methylene protons; at about 100°C both doublets coalesce to singlets. The possible intramolecular processes were studied with a complete permutational analysis. The experimental data can be explained by assuming a slow exchange up to 100°C, then a fast racemisation process starts in which a heteropolar breaking of a Pt‐ligand bond is involved.

The isomerization of trans‐ into cis‐Pt(Bu2dtc)2I2 was studied between −10° and + 35°C by proton NMR The activation parameters ΔH≠ = 17.2 kcal/mole and ΔS≠ = −17 eu suggest an ionic intermediate formed via rupture of a Pt‐I bond.
The direct synthesis of methylchlorosilanes: Kinetic measurements with a gas flow calorimeter
Authors: de Cooker M. G. R. T. , van Den Berg P. J.
Published: September 2010

The rate of the reaction of methyl chloride and silicon, copper functioning as a catalyst and zinc and aluminium as promoters, has been measured with a calorimeter. From the experimental results it follows that the calorimeter can be used to study the kinetics of the direct synthesis of methylchlorosilanes. At a temperature of 333°C and at pressures of 300–800 Torr the initial reaction rate can be described by the power function r = k Pn, with n, the order of the reaction with respect to methyl chloride, being equal to 0.94.
Determination of the optical purity and absolute configuration at the 2‐position of enzymatically prepared 2‐substituted prostaglandins
Authors: Bus J. , Korver O.
Published: September 2010

Circular dichroism measurements and proton magnetic resonance measurements with chiral shift reagents were used to determine possible chirality at the 2‐position of 2‐substituted prostaglandins. Measurements were carried out on the prostaglandin E1 (PGE1) molecules or 2‐substituted suberic acids obtained from them by an ozonisation procedure. The following conclusions may be drawn:

‐ In the PGE1‐forming reaction the enzyme exhibits a slight preference for one of the antipodes of the starting material.

‐ (2R)‐2‐methyl‐PGE1 and (2R)‐2‐phenyl‐PGE1 are preferentially formed.

‐ 2‐cyano‐PGE1 was also considered, but fast racemization prevented conclusions about the enzyme specificity.
Decomposition and disproportionation of hydrazyl radicals and hydrazo compounds derived from azo dyes
Authors: Heijkoop G. , van Beek H. C. A.
Published: September 2010

The mechanisms of decomposition and disproportionation of hydrazyl radicals and hydrazo compounds, derived from azo dyes, have been studied by flash photolysis, flow experiments and fluorescence spectrometry. The hydrazyl radicals undergo a combined decomposition and oxidation process, resulting in the formation of amines and iminoquinones, and regeneration of part of the amount of dye used in their preparation. Hydrazo compounds are formed upon further photo‐reduction of hydrazyl radicals, and decompose in a similar fashion as the latter.
Hydrogenation of Dewar‐benzene derivatives. II. Heterogeneous and homogeneous hydrogenation of dimethyl tetramethylbicyclo [2.2.0]hexa‐2,5‐diene‐2,3‐dicarboxylate and related compounds
Authors: van Rantwijk F. , Timmermans G.J. , van Bekkum H.
Published: September 2010

Dimethyl tetramethylbicyclo[2.2.0]hexa‐2,5‐diene‐2,3‐dicarboxylate (1) and some related compounds were hydrogenated in the presence of a number of Group VIII metal catalysts. Heterogeneous hydrogenation under ambient conditions resulted in exo,exo addition of one mole of hydrogen. The regioselectivity was strongly dependent on the catalyst, and on the nature and steric requirements of the substituents. Hydrogenation of 1 in the presence of a homogeneous platinum‐tin catalyst resulted in exclusive hydrogenation of the ester‐substituted double bond; exo,endo hydrogenation was involved for 16%.
Selective removal of phenolic hydroxyl groups of morphinan derivatives synthesis of rac. N‐formyl‐3‐methoxy‐6‐oxomorphinan (1)
Authors: Beyerman H.C. , Buurman E. , Lie T.S. , Maat L.
Published: September 2010

The hydroxyl group of N‐formyl‐2‐hydroxy‐3‐methoxy‐6‐oxomorphinan (7) can be readily etherified with 5‐chloro‐1‐phenyltetrazole. The etherification of isomers with the hydroxyl group in position 4 scarcely takes place, if at all. Catalytic hydrogenolysis of the ether of 7 gives dehydroxylation of 7 to N‐formyl‐S‐methoxy‐6‐oxomorphinan (1).
Vilsmeier formylation of vinylcyclopropanes II
Authors: Traas P.C. , Boelens H. , Takken H.J.
Published: September 2010

Vilsmeier formylation of vinylcyclopropanes 1 (c‐C3H5CR1CHR2, R1 = alkyl, cycloalkyl, phenyl and vinyl, R2 = hydrogen and alkyl), affords the corresponding 3‐cyclopropylacroleïns in excellent yields (75‐95%). Vinylcyclopropanes without an α‐substituent (R1 = H) react very sluggishly and give poor yields (10‐20%) with the exception of the parent compound, vinylcyclopropane (65%), and dehydrocycloisolongifolene (90%). The reaction is not‐stereospecific, supporting the intermediacy of a carbenium ion. Despite the interaction with a neighbouring cyclopropyl group the ring survives the formylation without being ruptured.

The reactivity towards the Vilsmeier reagent is very much affected by the size of the substituent on the reactive centre of the vinylcyclopropane system. In some cases double bond migration to the more stable or more accessible position is observed prior to formylation. The course of the former process is strongly influenced by the dimethylformamide concentration.
Regiospecific γ‐alkylation and acylation of 1,3‐cyclohexanedione enol ethers
Authors: de Groot Ae. , Jansen B. J. M.
Published: September 2010

Enol ethers of cyclic β‐diketones can be alkylated and acylated in high yields at C(6). When this position is blocked, alkylation takes place at C(2).
Réaction d'oximation de cétones II. Mécanisme de l'étape d'addition, structure et position de l'état de transition
Authors: Lamaty G. , Natat A. , Petitjean A. , Roque J. P.
Published: September 2010

Les constantes de vitesse d'addition neutre, ko, et acido‐catalysée, kH, de l'hydroxylamine sur l'acétone, la cyclohexanone, la cyclopentanone, la cycloheptanone et sur neuf acétophénones ont été mesurées dans l'eau à 25°. Les valeurs des constantes ρ de Hammett sont respectivement égales à +0,78 et +0,45 pour la réaction neutre et la réaction acido‐catalysée. Le mécanisme des deux additions et la structure de leurs états de transition sont discutés. Dans les deux cas le processus de transfert de proton parait être “concerté” et l'état de transition proche de l'état initial.
Ring transformations in reactions of heterocyclic compounds with nucleophiles (XII): A 15N and 14C study of the conversion of pyrimidine into 5‐ethyl‐2‐methylpyridine
Authors: Oostveen E. A. , van der Plas H. C.
Published: September 2010

The mechanism of the conversion of pyrimidine into 5‐ethyl‐2‐methylpyridine has been investigated. It has been proved, using the labelled compounds [1,3‐15N]pyrimidine, [4,6‐14C]pyrimidine and [5‐14C]pyrimidine, that this reaction proceeds via a mechanism, in which the pyrimidine ring is fragmentated into two molecules of HCN and one molecule of N‐methylacetaldimine. Four molecules of this imine undergo an aldol type condensation leading to 5‐ethyl‐2‐methylpyridine.
Bis(trichloromethanesulfenyl)amine from the reaction of nitrogen trichloride with dimethyl disulfide: Synthesis and reactions
Authors: Trompen W. P. , Geevers J.
Published: September 2010

Reaction of nitrogen trichloride with dimethyl disulfide in chloroform solution affords bis(trichloromethanesulfenyl)amine (2). Compound 2 is converted by trichloromethanesulfenyl chloride into tris(trichloromethanesulfenyl)amine (3) and by trifluoromethanesulfenyl chloride into bis‐(trichloromethanesulfenyl)trifluoromethanesulfenyl amine (4). Acylation of 2 with acetyl chloride and with benzoyl chloride respectively, is described The reaction of 2 with thionyl chloride affords sulfinyl‐(trichloromethanesulfenyl)amine (7).
Isomérisation d'azides intermédiaries dans la synthèse de phényl‐1 cyclohexylamines substituées au cyclohexane
Authors: Geneste P. , Kameuka J. M. , Herrmam P. , Moreau J.
Published: September 2010

An important step in a new synthesis of phenylcyclohexylamines, the conversion of 1‐phenylcyclohexanols into the corresponding azides, is studied in some detail. The slow epimerization of the azides allows isolation of both the kinetic and the thermodynamic products.

From the chemical behaviour of the different species in the reaction medium (alcohols, azides, ole fines) it is concluded that the common intermediate probably is a carbocation.
Deazapurine derivatives XV: Syntheses of some mono‐ and difluoroimidazo[4,5‐b]‐ and ‐[4,5‐c]pyridines
Authors: Kroon C. , van den Brink A. Maassen , Vlietstra E.J. , Salemink C.A.
Published: September 2010

The syntheses of 5‐fluoro‐, 5,7‐difluoroimidazo[4,5‐b]pyridine (5b and 5e”) and 4‐fluoro‐, 6‐fluoro‐ and 4,6‐difluoroimidazo[4,5‐c]pyridine (5a, 5c and 5e) are described. The syntheses are achieved through fluorodechlorination of di‐ and trichloro‐3‐nitropyridines, followed by monoamination, reduction and ring‐closure with diethoxymethyl acetate. The reactivity of the new fluoro‐imidazopyridines is investigated briefly.
The chemistry of small ring compounds. Part 32: Synthesis of some 1‐arylcyclopropanols and 1‐arylcyclopropyl chlorides
Authors: van der Vecht J.R. , Steinberg H. , de Boer Th.J.
Published: September 2010

The synthesis of some cyclopropanes with a trimethylsilyloxy group and an aryl group carrying electron‐donating substituents at the same ring carbon atom is described. These compounds can be used as precursors for 1‐aryl‐cyclopropanols and ‐cyclopropyl chlorides.
Reactive additives for polyethylene terephthalate I: Preparation of ketenimines
Authors: Sikkema D.J. , Molenaar E. , van Guldener D.B.
Published: September 2010

A number of synthetic routes to fully aromatic bisketenimines, versatile additives for processing polyethylene terephthalate into high‐performance tyre yarns, have been studied. A convenient procedure is presented here: conversion of a bis‐gem‐dichloroaziridine with sodium iodide or zinc.
Preparation, properties and crystal structure of hexakis(N,N‐di‐n‐butyldithiocarbamato)(copper(III), ‐copper(II), ‐gold(III)) tetrabromodi‐μ‐bromodimercurate(II), [(Cu2Au)(Bu2dtc)6][Hg2Br6]
Authors: Gal A.W. , Beurskens Gezina , Cras J.A. , Beurskens P.T. , Willemse J.
Published: September 2010

The preparation, some spectral properties and the crystal structure of a compound of composition [Cu2Au(Bu2dtc)6][Hg2Br6]*, are reported. The crystal structure is isomorphous with the tricopper analogue: [Cu3(Bu2dtc)6][Cd2Br6].

X‐Ray data for the present compound are: space group Pī; unit cell: a = 12.614(4), b = 13.691(4), c = 12.502(4) Å, α = 96.37(4)°, β = 91.47(4)°, γ = 85.43(4)°, with one formula unit per cell. Atomic parameters were refined to a conventional R‐value of 0.056 for 1752 independent non‐zero reflections. The structure consists of two ionic units: [Cu2Au(Bu2dtc)6]2+ and [Hg2Br6]2–. The non‐centric cation is situated at a centrosymmetric position, with disordered Cu(III) and Au(III) attached to a central Cu(II) atom.

This central Cu(II) atom has an apically distorted octahedral S‐coordination, with Cu–S distances of 2.33(1), 2.28(1), and 3.20(1) Å. The disordered [Cu(III), Au(III)] positions have five‐fold pyramidal S‐coordination with distances of 2.25(1), 2.26(1), 2.29(1), 2.26(1) and 3.15(1) Å.
Photodehydrocyclisations of stilbene‐like compounds XVI: Photoreactions of α‐(9‐phenanthryl)stilbene and 1‐(9‐phenanthryl)‐1‐phenylethylene
Authors: Laarhoven W.H. , Cuppen Th. J. H. M.
Published: September 2010

The regular photocyclisation of α‐(9‐phenanthryl)stilbene (1) to 9‐phenylbenzo[g]chrysene (2) is accompanied by formation of 4,5‐diphenylacephenanthrylene (3). A similar photocyclisation, providing a five‐membered ring, occurs on irradiation of 1‐(9‐phenanthryl)‐1‐phenylethylene (4) which yields a small amount of 5‐phenylacephenanthrylene (5). The structures of3and5were confirmed by comparison of their spectral data with those of acephenanthrylene (10). This was synthesized by photolysis of 1‐(o‐iodobenzylidene)indane (8), followed by dehydrogenation, however,10cannot be obtained by irradiation of 1‐(o‐iodobenzylidene)indene (11). The different photoreactivity of8and11is discussed briefly.
Esters β‐thiocétoniques cyclaniques N° 1 Préparation et séparation des isomères
Authors: Paquer D. , Smadja S.
Published: September 2010

Treatment of alicyclic β‐keto esters with a mixture of hydrogen sulfide and hydrogen chloride gives β‐thioxo esters.

In some cases three forms of these products have been characterized a thioketone form, a conjugated enethiol form and a non‐conjugated enethiol form.
Ring transformations in reactions of heterocyclic compounds with nucleophiles (XIII) Degenerate ring transformations of N‐methylpyrimidinium salts into 2‐substituted pyrimidines
Authors: Oostveen E.A. , van der Plas H.C. , Jongejan H.
Published: September 2010

On treatment of the quaternary pyrimidinium salts i.e. 1‐methyl‐4‐phenylpyrimidinium iodide and 1‐methyl‐5‐phenylpyrimidinium iodide with cyanamide, O‐methylisouronium chloride or bis[S‐methylisothiouronium] sulfate in basic media, 2‐amino‐4‐phenylpyrimidine and 2‐amino‐5‐phenylpyrimidine are formed respectively. A ring transformation is involved in which the two‐atom fragment N(1)‐C(2) of the pyrimidine ring is replaced by an N‐C fragment of the reagent. On reacting 1‐methylpyrimidinium iodide with benzamidinium chloride or pivalamidinium chloride in a solution of sodium ethoxide in ethanol, 2‐phenylpyrimidine and 2‐tert‐butylpyrimidine are formed respectively.

It is proved by 15N‐labelling that this nucleophilic substitution occurs via a ring transformation in which the N(1)‐C(2)‐N(3) fragment of the pyrimidine is replaced by the N‐C‐N fragment of the amidine. These reactions are new examples of a nucleophilic substitution occurring according to an SN(ANRORC) mechanism.
Synthesis of 1,5‐ and l,7‐naphthyridin‐4(1H)‐ones
Authors: Walraven H.G.M. , Choudry G.G. , Pandit U.K.
Published: September 2010

The reaction of 3‐aminopyridine with β‐keto esters followed by thermal cyclization of the corresponding 3‐aminoacrylic esters constitutes a convenient general approach to the synthesis of 1,5‐ and 1,7‐naphthyridine derivatives.
On the reaction of 3‐bromo(chloro)‐1,7‐naphthyridine with potassium amide in liquid ammonia
Authors: van der Plas H.C. , Woźniak M. , van Veldhuizen A.
Published: September 2010

3‐Amino‐ and 4‐amino‐1,7‐naphthyridine are obtained from both 3‐bromo‐ and 3‐chloro‐1,7‐naphthyridine on amination with potassium amide in liquid ammonia at −33°. The ratio in which the two amino compounds are formed is completely independent of the nature of the halogen atom, presenting good evidence for the intermediacy of 3,4‐didehydro‐1,7‐naphthyridine. 1HNMR spectroscopy has shown that 3‐chloro‐1,7‐naphthyridine forms with the amide ion a σ‐adduct at C‐2; in a very fast reaction; this adduct formation precedes the formation of the didehydro compound.
Ring expansion of geminal dibromocyclopropanes with silver fluoride. A convenient route to fluorinated medium‐sized rings
Authors: Loozen H.J.J. , Robben W.M.M. , Buck H.M.
Published: September 2010

Ring opening of the geminal dibromocyclopropanes 1−3 can be effected by treatment with silver fluoride in acetonitrile.

In a stereospecific reaction this affords the allylic fluorides 4−8 in moderate yields. This reaction follows the general principles which have been established for silver ion‐catalyzed ring expansions in medium sized rings.

Treatment of 7‐exo‐bromo‐7‐endo‐iodobicyclo[4.1.0]heptane (10) with AgF affords 2‐bromo‐3‐fluoro‐1‐cycloheptene (11). On using AgPF6 as a catalyst in the ring opening of 10, a Ritter reaction is observed giving N‐(2‐bromo‐1‐cycloheptene‐3‐yl)acetamide (12).
Eight‐coordinated 1,1‐dithio ligand complexes of molybdenum and tungsten
Authors: Nieuwpoort A. , Steggerda J.J.
Published: September 2010

The physical properties of the dithiocarbamato compounds Mo(R2dtc)4 (R2dtc = R2NCS2−; R = Me, Et, i‐Pr, Bz, Ph; R2 = Tm, Pm, MeBz; Tm = (CH2)4, Pm = (CH2)5) and [M(R2dtc)4]X (M = Mo, W; X = various anions), and the dithio acid compounds M(Rdta)4 (M = Mo, W; Rdta = RCS2−; R = Tol, Naf; Tol = p‐toluoyl, Naf = 2‐naphthoyl), prepared by oxidative decarbonylation of metal carbonyl complexes with disulfides, have been investigated. Conductivity data and infrared spectra indicate that all compounds contain metal ions coordinated by eight sulfur atoms belonging to four ligands.

Voltammetric measurements show for the [Mo(R2dtc)4]°,+ complexes three one‐electron oxidation/reductions, indicating the formation in solution of unstable [Mo(R2dtc)4]− and [Mo(R2dtc)4]2+. The [W(R2dtc)4]+ complexes show only one oxidation and one reduction process in the voltage range studied. The substituent effects on the half‐wave potentials can be described by the Taft relation. The dithio acid complexes show two redox processes, indicating the formation of M(II) and M(V) compounds. The differences between these complexes and the dithiocarbamato complexes are in agreement with the stronger electron donating properties of the dtc ligand.
Photochemical hydroxylation of quinoxalines
Authors: Verbeek J. , Berends W. , van Beek H.C.A.
Published: September 2010

Irradiation of quinoxaline (1) in acidic aqueous solution under anaerobic conditions leads to the formation of 5‐hydroxyquinoxaline (4) and the 1,4‐dihydroquinoxaline radical cation (5). The radical cation (5) was characterized by ESR spectroscopy.

Under aerobic conditions 5‐hydroxyquinoxaline (4) is the only irradiation product formed. The effect of substituents attached to the benzene nucleus of quinoxaline is analyzed.
Two‐step synthesis of a sex attractant of the male Boll Weevil from isophorone
Authors: Traas P.C. , Boelens H. , Takken H.J.
Published: September 2010

Vilsmeier formylation of isophorone affords (3‐chloro‐5,5‐dimethyl‐2‐cyclohexenylidene)acetaldehyde (2) in 80 % yield.

Catalytic hydrogenation of this unsaturated aldehyde over palladium on charcoal poisoned with sulfur and quinoline gives in quantitative yield (3,3‐dimethylcyclohexylidene)acetaldehyde†, an important component of the sex pheromone complex of the male Boll Weevil (Anthonomus Grandis).
Conversion of (‐)‐N‐formylnordihydrothebainone into (‐)‐dihydrotbebainone and vice versa: (Chemistry of opium alkaloids, Part VII)
Authors: Beyerman H.C. , van Bommel L. , Maat L. , Olieman C.
Published: September 2010

(‐)‐N‐Formylnordihydrothebainone (1) was converted into (‐)‐dihydrothebainone (3) by two routes: removal of the formyl group followed by reductive methylation, and direct hydride reduction after protection of the 6‐oxo group in the form of an acetal.

The starting material 1 was obtained by demethylation of (‐)‐dihydrothebainone (3), prepared from natural material, to (‐)‐nordihydrothebainone (2), which was formylated with ethyl formate.
C‐Nitroso compounds. Part XXVIII: Generation and reactivity of N‐(1‐chloroalkyl)nitrones obtained by reaction of diazoalkanes with gem‐chloronitroso compounds
Authors: Kayen A. H. M. , de Boer Th. J.
Published: September 2010

Hitherto unknown N‐(1‐chloroalkyl)nitrones 1, the formal condensation products of ketones and gem‐chloro(hydroxylamino)alkanes have been generated in situ by reaction of diazoalkanes with gem‐chloronitrosoalkanes 3. The existence of transient nitrone species follows from their reaction with tert‐butoxy radicals and with tri‐n‐butylstannane to give nitroxides, the structure of which is supported by ESR.

In situ generated N‐(1‐chloroalkyl)nitrones 1 undergo methanolysis in the presence of bases with formation of two oximes and two ketones. This strongly implies a mechanism of solvolysis as outlined in schemes 1 and 2, supported by quantitative product analysis (Table I).
Charge transfer complexes of tetracyanoquinodimethane with 6‐ and 7‐aminoquinolines
Authors: Poradowska H. , Czuba W. , Lorenz K. , Chyla A.
Published: September 2010

Charge transfer complexes of tetracyanoquinodimethane with 6‐ and 7‐aminoquinolines have been obtained and their electrical and spectral properties investigated. These complexes possess high conductivities.
Synthesis of acetals using molecular sieves III The use of solid acids as catalysts
Authors: Wortel Th. M. , Esser W. H. , van Minnen Pathuis G. , Taal R. , Roelofsen D. P. , van Bekkum H.
Published: September 2010

The synthesis of acetals from the corresponding carbonyl compounds and alcohols in high yield is described. Commercial silica‐alumina cracking catalysts, Y‐type molecular sieves partially exchanged with multivalent cations and sulfonated polystyrene resins are used as catalysts while a molecular sieve type A serves to shift the equilibrium by adsorbing the water formed. Proper activation of silica‐alumina and Y‐sieve catalyst is essential for obtaining a high catalytic activity. Procedures have been developed to regenerate the catalyst‐adsorbent combination.

Compared to earlier techniques the synthesis of acetals has been improved substantially.
Stereochemistry of the reduction of some 2,2,4,5‐tetrasubstituted 1,3‐cyclopentanediones
Authors: Plantema O. G. , de Koning H. , Huisman H. O.
Published: September 2010

The reduction of the oxo functions in ethyl 5‐(6‐ethoxycarbonylhexyl)‐3,3‐dimethyl‐2,4‐dioxocyclopentanecarboxylate (1) with NaBH4, with LiAlH(O‐t‐Bu)3 and by catalytic hydrogenation is described. Four isomeric hydroxycyclopentanones and four isomeric cyclopentanediols were isolated and their stereochemistry was determined, providing 1H‐NMR and 13C‐NMR data which should be useful in structural assignment of isomeric prostaglandin analogues.
Ring transformations in reactions of heterocyclic compounds with nucleophiles Reactions of 4(6)‐alkoxy‐1‐ethyl‐ and 4,6‐dialkoxy‐1‐ethyl‐pyrimidinium tetrafluoroborates with liquid ammonia
Authors: Oostveen E.A. , van der Plas H.C.
Published: September 2010

On treatment with liquid ammonia at −33° the quaternary pyrimidinium salts i.e. 4‐ethoxy‐1‐ethyl‐ (1) and 4,6‐diethoxy‐1‐ethyl‐pyrimidinium tetrafluoroborate (3) undergo amino‐de‐ethoxylation, yielding 1,4‐dihydro‐1‐ethyl‐4‐imino‐pyrimidine hydrogen tetrafluoroborate (7) and a mixture of 1,4‐dihydro‐6‐ethoxy‐1‐ethyl‐4‐imino‐ (9) and 1,6‐dihydro‐4‐ethoxy‐1‐ethyl‐6‐imino‐pyrimidine hydrogen tetrafluoroborate (11), respectively. 1HNMR and 13CNMR spectroscopic evidence is presented for the fact that compounds 1 and 3 easily give σ‐adducts at position 2. Using 15N‐labelled ammonia it was shown that in these amino‐de‐ethoxylation reactions the substitution at C(4) or C(6) does not involve ring opening but probably occurs via an SN(AEn) process. Reaction of 4‐ethoxy‐1‐ethyl‐2‐phenyl‐ (2), 6‐ethoxy‐1‐ethyl‐4‐phenyl‐ (4), 4,6‐dimethoxy‐1‐ethyl‐2‐phenyl‐ (5) and 4,6‐dimethoxy‐1‐ethyl‐2‐methyl‐pyrimidinium tetrafluoroborate (6) with liquid ammonia gives besides the amino‐de‐ethoxylation product degenerate ring transformations leading to the N‐de‐ethylated products 14–16 and 4(6)‐(ethylamino)pyrimidines 17‐19. The salt 11 and 1,6‐dihydro‐1‐ethyl‐6‐imino‐4‐phenylpyrimidine hydrogen tetrafluoroborate (12) undergo, with potassium hydroxide, a Dimroth rearrangement to pyrimidines 20 and 17, respectively.
Recognition of atropisomerism and thermally labile prochirality, and measurement of barriers to rotation in sulfines (thione oxides) by the use of chiral shift reagents
Authors: Tangerman A. , Zwanenburg B.
Published: September 2010

The sulfines 1–9 in which the o‐positions of the aryl ring A are substituted by methyl groups, have a high rotational barrier about the aryl A to sulfine bond (bond α). Due to this α‐barrier, sulfines 1 and 2 exist as a pair of rotational enantiomers (atropisomerism). The symmetrically substituted sulfines 3,4,7,8 and 9 possess a prochiral centre, viz. the mesityl‐CSO part, provided rotation about bond α is restricted. With rapid rotation about bond α this prochirality disappears (thermally labile prochirality). Chiral lanthanide shift reagents are employed to uncover these chiral properties. The atropisomerism in the sulfines 1 and 2 and the thermally labile prochirality in the sulfines 3,4, 7, 8 and 9 are demonstrated by use of chiral shift reagent. Moreover, chiral shift reagents are successfully used to determine the α‐barrier in the sulfines 3, 4 and 9.
On the formation of allenes in the steroid series III.: Synthesis and reactions of 3‐methoxy‐17α‐hydroxy‐17β‐ethynyl‐1,3,5(10)‐estratriene (“epimestranol”)
Authors: van Dijck L.A. , Lankwerden B.J. , Vermeer J.G.C.M.
Published: September 2010

“Epimestranol” (6) has been prepared from the 16α,17‐epoxide 5 by reduction with LiAlH4. The structures of several by‐products have been elucidated and a mechanism for their formation is discussed. Both “mestranol” (3) and “epimestranol” failed to form p‐tosylates and only “mestranol” could be converted into the p‐toluenesulfinate which readily rearranged to the allenic sulfone 14. “Epimestranol” was transformed into a mixture of the two epimeric 17‐sulfones instead of the 17α‐sulfinate.
Synthesis of L‐Nπ‐methylhistidine derivatives (Imidazole chemistry, Part III)
Authors: Beyerman H. C. , Maat L. , Noordam A. , van Zon A.
Published: September 2010

L‐Histidine was converted into the methyl ester of (‐)‐(S)‐2‐chloro‐3‐(5‐imidazolyl)‐propionic acid (1). After benzoylation and reaction with trimethyloxonium fluoroborate, this yielded selectively the Nπ‐methyl compound, which was subsequently reduced to the corresponding chloro alcohol (4). The absolute configurations are confirmed by the optical rotatory dispersion and circular dichroism spectra.
Photolysis of some N‐cycloalkyl‐N‐nitrososulfonamides. The interaction between a small cycloalkyl group and an amidyl radical centre
Authors: Dekker E. E. J. , Engberts J. B. F. N. , de Boer Th. J.
Published: September 2010

N‐Cycloalkyl‐N‐nitrosotosylamides 1a‐c with three‐, four‐ and five‐membered cycloalkyl groups have been photolysed in CFCl3. The cyclopropyl derivative 1a isomerises to 2a, an imine containing a C‐nitroso group, by successive N‐NO homolysis and overall migration of the nitroso group from nitrogen to carbon (cf. Scheme 2). In methanol the solvent adds to the imine double bond. The cyclopentyl derivative 1c does not undergo isomerisation at all, but after N‐NO homolysis, the remaining radical 4c eliminates β‐hydrogen from the ring, thus forming the imine 7c with an unruptured ring. Alternatively, the radical 4c abstracts hydrogen from the solvent to give the N‐cyclopentyl‐sulfonamide 6c (cf. Scheme 3).

The cyclobutyl derivative 1b takes an intermediate position, and is therefore incorporated in both schemes. It shows a strong influence of the temperature (−10° to −80°) on the ratio of ring‐closed vs. ring‐opened products (cf. Table I).

Quenching experiments suggest that in all cases products are derived from singlet excited states.
Heavy‐atom effects in the photoreactions of halogenated aromatic compounds
Authors: Ruzo L.O. , Sundström G. , Hutzinger O. , Safe S.
Published: September 2010

The photoreactions of various halogenated naphthalenes and biphenyls in methanol at 290‐310 nm are affected by addition of heavy‐atom lithium salts. The triplet decay rate appears to be increased relative to the reaction rate resulting in overall rate decrease. The effect of iodide is greater than that of added bromide while the reaction rates in the presence of chloride or in the absence of external heavy atoms proceed in the order of decreasing bond strength of the carbon‐halogen bonds.
Réactions de condensation avec des carbanions de sulfonyl cétones. Propriétés chimiques des composés d'addition
Authors: Ladurée D. , Paquer D. , Rioult P.
Published: September 2010

The dianions from a number of α‐sulfonyl ketones have been obtained using sodium hydride and n‐butyllithium. The dianions can produce with carbon disulfide, S‐dimethyl dithiocarbonate or dimethyl trithiocarbonate different addition compounds. The chemical reactions of these compounds with phosphorus pentasulfide, phenylhydrazine and methanol (in acid medium) have been investigated.
Reactivity of ring systems with two hetero atoms. I. On the reaction of 1,4‐dithiins with n‐butyllithium
Authors: Schoufs M. , Meyer J. , Vermeer P. , Brandsma L.
Published: September 2010

The reaction of 1,4‐dithiin (1) with n‐butyllithium has been examined. At −110° in tetra‐hydrofuran 2‐lithio‐1,4‐dithiin (2) is sufficiently stable to allow of the preparation of derivatives. Anion (2) undergoes ring opening by a 1,2‐elimination at −60°; subsequent methylation and hydrolytic work‐up gives ZHC≡CS‐CHCHSMe (6), or Z−MeC≡C−S−CHCH−SMe (7). At about −5° butyllithium attacks sulfur in the intermediary Z−LiC≡C−S−CHCH−SLi (4), leading to Z−BuS−CHCH−SLi (8), and LiC≡CLi.

These results are not in agreement with the mechanism proposed by Parham et al. for benzo‐1,4‐dithiin and 2,5‐diphenyl‐1,4‐dithiin. We studied also the reactivity of 2,6‐dimethyl‐1,4‐dithiin (13), and 2,6‐ di‐tert‐butyl‐1,4‐dithiin (25), towards butyllithium. Starting from 13 the otherwise, difficultly accessible tri‐ and tetramethyl‐1,4‐dithiins could be prepared in high yield.

The ring opening provides a valuable method for the synthesis of stereochemically pure Z‐1‐(alkynylthio)‐2‐(alkylthio)alkenes and Z‐1‐(butylthio)‐2‐(alkylthio)alkenes.
A novel synthesis of 10‐aryl‐9‐arsaanthracenes
Authors: Weustink R.J.M. , Jongsma C. , Bickelhaupt F.
Published: September 2010

10‐Aryl‐9‐arsaanthracenes (3b,c,d) were conveniently synthesized by flash vacuum pyrolysis at ∼ 500° of 10‐mono‐ and di‐substituted 9‐aryl‐9,10‐dihydro‐9‐arsaanthracenes (11a‐f). The yield of 10‐aryl‐9‐arsaanthracenes is found to depend upon the substituents at C(10). The occurrence of radical intermediates is discussed briefly.
Synthesis of 9,11‐dideoxy‐9a‐homoprostaglandins
Authors: Eggelte T.A. , de Koning H. , Huisman H.O.
Published: September 2010

The synthesis of three 9,11‐dideoxyprostaglandins in which the cyclopentane moiety is replaced by a six‐membered ring, is described. Starting from phthalaldehydic acid (1) the aromatic PG‐analogue, 7‐[2‐(3‐hydroxy‐(E)‐1‐octenyl)phenyl]heptanoic acid (9), was prepared in 7 steps in 49% overall yield. The cis‐substituted cyclohexane PG‐analogue, ethyl 7‐[cis‐2‐(3‐hydroxy‐(E)‐1‐octenyl)cyclohexyl]heptanoate (34), was obtained in 7 steps in 53% overall yield from the same starting material 1. The trans‐substituted cyclohexane PG‐analogue, ethyl 7‐[trans‐2‐(3‐hydroxy‐(E)‐1‐octenyl)cyclohexyl]heptanoate (20), was synthesized from methyl 9‐cyano‐(E)‐2‐nonenoate (12) in 8 steps in 34% yield.
The substitutional incorporation of Fe(III) and Cr(III) ions within gibbsite by homogeneous precipitation
Authors: van Dijk J.
Published: September 2010

Fe(III) and Cr(III) have been incorporated in gibbsite (∼ 1%) by oxidation of a Fe(III)‐triethanolamine complex with Cl2 and reduction of K2CrO4 with hydrazine at an appropriate rate, during the precipitation of gibbsite from an alkaline aluminate solution. The products show characteristic single ion ESR spectra.
Phosphite triesters of methyl α‐D‐ and methyl β‐D‐ribopyranoside
Authors: Bellaart A. C. , Buck H. M. , Leclercq P. A. , van de Ven L. J. M.
Published: September 2010

The phosphites of methyl α‐D‐ and methyl β‐D‐ribopyranoside were prepared from the corresponding methylglycosides according to the method of Stetter and Steinacker1. The mass spectra of the isomeric phosphites, which are markedly different, and the NMR spectral data are in agreement with the proposed structures.
Interaction between functional groups in low‐molecular‐weight polyfunctional compounds
Authors: van Treslong C. J. Bloys
Published: September 2010

From experimental values of the ionization constants of low‐molecular‐weight poly‐functional acids and bases a consistent picture regarding the interaction between the functional groups, in both the uncharged and charged states, can be evaluated. Assuming simple additivity for both interaction effects, calculations on various series of homologous compounds result in uniform values for both effects.
Chemical shifts and substituent effects in the PMR spectra of substituted isoquinolines
Authors: Sanders Georgine M. , van Dijk M. , van Veldhuizen A.
Published: September 2010

Chemical shifts of H‐l, H‐3 or H‐4 are given for 19 mono‐ and 30 di‐substituted isoquinolines, carrying halogeno, amino, ethoxy or phenyl substituents in the pyridine nucleus. For the disubstituted isoquinolines, δ‐values calculated on the basis of additivity, agree with the experimental values.
On the reaction of 2‐, 3‐ and 4‐bromo(chloro)‐1,8‐naphthyridine with potassium amide in liquid ammonia
Authors: van der Plas H. C. , Woźniak M. , van Veldhuizen A.
Published: September 2010

Evidence has been presented for the occurrence of 3,4‐didehydro‐1,8‐naphthyridine in the reaction of 3‐bromo(chloro)‐ and 4‐bromo(chloro)‐1,8‐naphthyridine with potassium amide in liquid ammonia. The addition ratio of the amide ion (ammonia) to C(3) and C(4) in the didehydro bond was found to be 43/57, which is nearly identical with that found in 3,4‐didehydroquinoline, 3,4‐didehydro‐1,7‐naphthyridine and 3,4‐didehydro‐1,6‐naphthyridine. It was calculated that 39% of the 4‐amino compound, obtained from the 4‐bromo‐1,8‐naphthyridine is formed by an SN(AE) process. In the reaction of 3‐chloro‐1,8‐naphthyridine with potassium amide, besides the 3‐amino and 4‐amino compounds, 2‐amino‐3‐ethynylpyridine and 3‐ethynyl‐2‐(formylamino)pyridine were obtained, indicating a fission of the bond between C(2) and C(3). The last mentioned compound is also formed in the reaction of 4‐chloro‐1,8‐naphthyridine. 1H‐NMR spectroscopy has shown that 3‐bromo(chloro)‐1,8‐naphthyridine forms with the amide ion a σ‐adduct at C(2); this adduct formation preceded the formation of the didehydro compound. 2‐Bromo(chloro)‐1,8‐naphthyridine gave exclusively 2‐amino‐1,8‐naphthyridine. Conclusive evidence was obtained that part of the 2‐amino compound was formed by a tele‐substitution SN(AE)tele involving the 7‐amino‐2‐chloro(bromo)‐7,8‐dihydro‐1,8‐naphthyridine (27% in the case of the 2‐bromo compound, 8% in the case of the 2‐chloro compound).
Carbohydrate separation by X‐zeolites. Cation and solvent effects
Authors: Wortel Th. M. , van Bekkum H.
Published: September 2010

The adsorption of fructose and glucose on X‐zeolites has been studied. The adsorption capacity and the selectivity of adsorption depend on the type of cation in the zeolite, the extent of cation exchange and the solvent used. Fructose and glucose can be conveniently separated by column chromatography using NaCaX as the stationary phase and eluting with aqueous methanol. This system also allows separation of other monosaccharides, of monosaccharides and disaccharides, and of monosaccharides and related alditols.
N‐Nitroso‐5‐methyl‐1,3‐oxazolidine identified as an impurity in a commercial cutting fluid
Authors: Stephany R. W. , Freudenthal J. , Schuller P. L.
Published: September 2010

The title N‐nitrosamine was detected in a mineral oil cutting fluid concentrate up to 30 mg per kg. Compound identification was performed by gaschromatography‐mass spectrometry and synthesis. A possible route of formation of the detected N‐nitrosamine starting from 1‐amino‐2‐propanol is suggested.
Crystal and molecular structure of N,N′‐[bis(tosylmethyl)]urea. Conformational preferences and non‐bonded interactions
Authors: Visser R. J. J. , Vos A. , Tel R. M. , Engberts J. B. F. N.
Published: September 2010

The room temperature crystal and molecular structure of the title compound have been determined by direct methods from diffractometer data. Crystals are monoclinic, a = 12.809(2). b = 9.182(7), c = 17.719(6) Å, β = 116.09(2)°, space group P21/c, Z = 4. The structure was refined by anisotropic least‐squares to R = 0.099 for 1944 independent reflections. The molecule resides in a conformation in which the tosyl rings face each other, so that there roughly is a mirror plane through the CO bond and perpendicular to the NCON plane.

Each carbonyl oxygen atom is hydrogen bonded to both nitrogen‐hydrogen atoms of a neighbouring urea moiety. Potential energy calculations suggest that the conformational preferences are mainly caused by non‐bonded interactions as described by atom‐atom interaction functions of the Buckingham type.
Chemistry of 2H‐thiopyran and derivatives I. 2H‐ versus 6H‐proton abstraction from 2H‐thiopyran
Authors: Gräfing R. , Brandsma L.
Published: September 2010

Depending on the nature of the base/solvent system deprotonation at carbon atoms 2 and 6 in 2H‐thiopyran 1 can be carried out specifically. Conversion of 6‐lithio‐2H‐thiopyran (4) into the charge‐delocalised species 2 takes place in the presence of diisopropylamine, probably via a process of proton donation and abstraction. Addition of hexamethylphosphoric triamide (HMPT) to the solution of 4 also gives rise to the formation of the thermodynamically more stable species 2.
Cationic heterocyclisation One‐step synthesis of condensed heterocyclics
Authors: Wijnberg J. B. P. A. , de Boer J. J. J. , Speckamp W. N.
Published: September 2010

Acid treatment of N‐aryl‐5‐hydroxy‐2‐pyrrolidinones and their ethers obtained from N‐arylsuccinimides by means of NaBH4/H+ reduction leads to mixtures of dimeric coupling products which may give additional ring closure with the N‐aryl substituent.
Restricted rotations in configurational assignments: The Diels‐Alder adduct of 1,3,5‐cycloheptatriene and maleic anhydride
Authors: Verma Shiva Mohan , Singh M. Dhaneshwar
Published: September 2010

The configuration of the Diels‐Alder adduct of 1,3,5‐cycloheptatriene (CHT) and maleic anhydride has been investigated using 1H‐NMR spectroscopy. Evidence for the endo‐cis‐endo‐configuration and the tricyclo[3.2.2.02′4]nonane skeleton of the adduct has been provided by the 1H‐NMR spectra observed for the various derivatives of the adduct. While non‐planar conformations about the N‐N′ bond in N‐(diacylamino)imides of the adduct have been utilized in establishing the orientation of the anhydride ring, the bromination of the double bond of the adduct (exo‐cis‐addition) has demonstrated the configuration of the cyclopropane ring.
Inherently chiral olefins. Synthesis and resolution of 4‐(9‐fluorenylidene)‐1,2,3,4‐tetrahydrophenanthrene
Authors: Feringa Ben , Wynberg Hans
Published: September 2010

The reductive coupling of 4‐keto‐1,2,3,4‐tetrahydrophenanthrene with 9‐fluorenone and acetone is described. The inherently chiral 4‐(9‐fluorenylidene)‐1,2,3,4‐tetrahydrophenanthrene was resolved chromatographically and chiroptical properties are presented.
Synthesis of N,N‐phthaloyl‐L‐valine and N,N‐phthaloyl‐L‐isoleucine with N‐(ethoxycarbonyl)phthalimide
Authors: Adriaens P. , Meesschaert B. , Janssen G. , Dumon L. , Eyssen H.
Published: September 2010

The synthesis of N,N‐phthaloyl‐L‐valine and N,N‐phthaloyl‐L‐isoleucine with N‐(ethoxycarbonyl)phthalimide, using a modification of the method of Nefkens, Tesser and Nivard, is described. When aqueous solutions of the sodium salts of the amino acids are stirred at room temperature with a 10% excess of N‐(ethoxycarbonyl)phthalimide, dissolved in ethyl acetate, the main products formed are N‐[N‐(ethoxycarbonyl)phthalamoyl]‐L‐valine or N‐[N‐(ethoxycarbonyl)phthalamoyl]‐L‐isoleucine. The presence of these intermediates confirms the reaction mechanism proposed by Nefkens et al. Refluxing these compounds in toluene gives good yields of optically pure phthaloyl‐L‐valine and phthaloyl‐L‐isoleucine. From the synthesis of phthaloylvaline, N‐(ethoxycarbonyl)phthalamic acid and minor amounts of phthalic acid, valine and the phthalamic acid derivative from phthaloylvaline were identified as by‐products.
Addition and substitution reactions of hexahelicene: Bromination, nitration and acetylation
Authors: op den Brouw P. M. , Laarhoven W. H.
Published: September 2010

Bromine adds to hexahelicene at the C(5)‐C(6) and C(11)‐C(12) bond. The addition products eliminate hydrogen bromide on heating above 100°C, yielding mainly 5‐bromo‐ and 5,12‐dibromohexahelicene, respectively. The same elimination reactions occur on chromatography of the addition products over silica gel or alumina. In pyridine or triethylamine, however, bromine is eliminated.

Bromination in the presence of iodine yields also the substitution products 5‐bromo‐ and 5,12‐dibromohexahelicene. Nitration and acetylation are less selective, but under sufficiently mild conditions 5‐ and 5,12‐substitution products can very well be obtained; in both cases an 8‐substituted hexahelicene can be isolated as a second product.

Although several reactivity parameters (Nr, Fr and μr values) predict high reactivity towards electrophiles at C(5) the high selectivity of the aromatic substitutions could not be foreseen from Fr (and Nr) values, whereas μr values predict higher reactivity at C(3) than at C(8).
1H‐ and 13C‐NMR studies of σ‐adducts of 1,2,4‐triazine and some of its derivatives with amide ions and/or liquid ammonia
Authors: Rykowski A. , van der Plas H. C. , van Veldhuizen A.
Published: September 2010

Unambiguous 1H‐ and 13C‐NMR spectroscopic data have been presented for the formation of σ‐adducts between a series of 1,2,4‐triazines and amide ions and/or liquid ammonia at C(5) of the 1,2,4‐triazine nucleus.
Photochemical radical chain dehalogenation of some simple organic halogen compounds
Authors: van Beek H. C. A. , van Der Stoep H. J.
Published: September 2010

Tetrachloromethane and hexachloroethane can be photoreduced with a high quantum yield in solutions of acetone and an alcohol. The reducing agent in this reaction is the ketyl radical, formed after hydrogen abstraction from the alcohol by the trichloromethyl radicals or pentachloroethyl radicals. The overall reaction is a radical chain process, in which the ketyl radicals and the trichloromethyl or pentachloroethyl radicals are the propagating species. Other polyhalogeno aliphatic compounds can be photoreduced in a similar fashion.
Biomimetic total synthesis of steroids II: Stereoselective synthesis of 7α‐methyl‐19‐norsteroids
Authors: Groen M. B. , Zeelen F. J.
Published: September 2010

The cationic cyclization of 3‐methyl‐2‐[6(m‐methoxyphenyl)‐5‐methyl‐(E)‐3‐hexenyl]‐2‐ cyclopentenol (4) was investigated. The major products were 1‐ and 3‐methoxy‐7α,17‐dimethyl‐1,3,5(10),13(17)‐gonatetraene (12 and 13a) indicating high asymmetric induction by the methyl substituent. Compound 13a was converted into DL‐7α‐methylestrone methyl ether (15a).
Derivatives of cis‐NPCl2(NSOCl)2 and (NPCl2)2NSOCl. Part VII. Isothiocyanato derivatives of (NPCl2)2NSOF, (NPCl2)2NSOPh and trans‐NPCl2(NSOPh)2
Authors: Klei E. , van de Grampel J. C.
Published: September 2010

Some isothiocyanato derivatives of (NPCl2)2NSOF, (NPCl2)2NSOPh and trans‐NPCl2‐(NSOPh)2 are prepared by reaction of these compounds with KSCN. The fully substituted derivatives are white crystalline solids, whereas NPCl2NP(NCS)2NSOF is a colourless liquid at room temperature. The mono‐isothiocyanato derivatives NPCl2NPClNCSNSOF and NPCl2NPClNCSNSOPh consist of mixtures (∼ 1:1) of two isomers. It is shown that substitution by NCS groups proceeds via a geminal pathway. The compounds are characterized by spectroscopic methods.
Attempted syntheses of 9‐stibaanthracene and 10‐phenyl‐9‐stibaanthracene
Authors: Bickelhaupt F. , Lourens R. , Vermeer H. , Weustink R. J. M.
Published: September 2010

Attempts were undertaken to prepare 9‐stibaanthracene (2c) and its 10‐phenyl derivative (3c). Both compounds proved to be too unstable for isolation; their possible occurrence as intermediates is discussed briefly.
C‐Nitroso compounds. Part XXXII. Reaction of α‐chloro nitroso compounds with alkyl substituted allenes. A route to cross‐conjugated aliphatic ketonitrones
Authors: Schenk C. , de Boer Th. J.
Published: September 2010

Reaction of α‐chloro nitroso compounds with tetramethylallene gives rise to the formation of hitherto unknown crystalline cross‐conjugated nitrone hydrochlorides 3, which can be converted into free nitrones 4 upon treatment with liquid ammonia. The reaction between 2‐chloro‐2‐nitrosoadamantane and 3‐phenyl‐1,2‐butadiene proceeds equally well, but with other α‐chloro nitroso compounds and with other alkylallenes only complicated mixtures are obtained, which contain the corresponding nitrone hydrochlorides as judged from hydrolysis to ketone and oxime 6.
Biomimetic total synthesis of steroids III: Stereoselective synthesis of 11α‐methyl‐19‐norsteroids
Authors: Groen M. B. , Zeelen F. J.
Published: September 2010

The synthesis and cationic cyclization of 2‐[6‐(3‐methoxyphenyl)‐2‐methyl‐(E)‐3‐hexenyl]‐3‐methyl‐2‐cyclopentenol (12) was investigated. The major cyclization products were 1‐ and 3‐methoxy‐11α,17‐dimethyl‐1,3,5(10),13(17)‐gonatetraene (14a and 15a) indicating a high degree of asymmetric induction by the pro‐C(11) chiral centre. Compound 15a was converted into DL‐11α‐methylestrone methyl ether (18).
Chemistry of electron‐rich conjugated polyenes III. Synthesis and acid hydrolysis of 2,2‐di‐ and 2,2,5‐trimethoxy‐5,6‐dihydropyrans
Authors: van Balen H. C. J. G. , Broekhuis A. A. , Scheeren J. W. , Nivard R. J. F.
Published: September 2010

Carbonyl compounds, activated by electron‐withdrawing groups, add to 1,1‐dimethoxybutadiene (Ia), yielding 2,2‐dimethoxy‐5,6‐dihydropyrans (IIa). 1,1,4‐Trimethoxybutadiene (Ib) reacts in a similar way with suitably activated ketones, but gives[2 + 2]‐cycloadditions with activated aldehydes. The different behaviour is ascribed to steric factors. Acid hydrolysis of the 2,2‐dimethoxydihydropyrans yields α,β‐unsaturated esters and corresponding lactones, or dienyl esters depending on the reaction conditions used.

1,1‐Dimethoxy‐3‐(trimethylsilyloxy)butadiene (Ic) yields Diels‐Alder adducts even with non‐activated carbonyl compounds, when zinc chloride is used as a catalyst. The products can be converted into dihydro‐γ‐pyrones by treatment with protic solvents (e.g. methanol).