bluuebunny/crossref_metadata_2025 huggingface dataset:
UV spectroscopy and structures of α‐bis(methoxyimino)alkanes
Authors: Stunnenberg Frank , Cerfontain Hans , Goubitz Kees , Heydenrijk Dick , Stam Caspar H.
Published: September 2010

The UV spectra of the geometric isomers of the α‐bis(methoxyimino)alkanes I‐8 and the structurally related conjugated (methoxyimino)isoxazolines 11 and 13 all exhibit a ππ* absorption band, of which the maxima with cyclohexane as solvent are between 216 and 268 nm, and 258 and 282 nm, respectively. The differences in λmax are discussed in terms of variations in the degree of inter‐iminyl conjugation, as a result of (i) variations in the inter‐iminyl dihedral angle due to steric hindrance and (ii) variations in the ring strain and/or the dipolar repulsion of the two methoxyimino moieties, as with the three geometric isomers of the four‐membered ring compound 1. The lower λmax of (E,E)‐8 compared to (E,E)‐4 is ascribed to a lower degree of cross‐conjugation of the phenyl group with the planar α‐bis(methoxyimino) chromophore in the former compound; the absorption band of (E,E)‐8 is, in fact, similar to that of the aliphatic (E,E)‐5. The energy of the ππ* absorption maximum of the (E,E)‐α‐bis(methoxyimino)alkanes appears to be linearly related to that of the corresponding (E)‐α‐oxo oxime ethers with a slope close to unity, illustrating that the sensitivity for structural variations is very similar for the two types of compounds.

X‐ray structure analysis showed the O‐N = C‐C = N‐O chromophore of (E,E)‐5, (E,E)‐8 and the (hydroxyimino)isoxazoline (E)‐10 in the crystalline state to be all planar within the limits of detection.
Synthesis of functionalized amino acids by ring‐opening reactions of aliphatically substituted aziridine‐2‐carboxylic esters
Authors: Legters Johan , Willems Johannes G. H. , Thijs Lambertus , Zwanenburg Binne
Published: September 2010

Nucleophilic ring‐opening reactions of 3‐alkylaziridine‐2‐carboxylic esters are described. Without ring activation at nitrogen, ring opening could only be accomplished with ethereal hydrogen chloride. Introduction of electron‐withdrawing activating groups at the nitrogen atom was necessary. Three types of activating groups were used, viz. acyl, alkoxycarbonyl and sulfonyl groups. In the presence of a Lewis‐acid catalyst, ring opening with two nucleophiles, namely indole and benzenethiol, could be accomplished. SN2‐type attack at C3 was observed exclusively. With Brönsted acids (hydrogen chloride, formic acid, acetic acid), ring opening could also be effected. 3‐Formyloxy derivatives could also be prepared by reaction of the activated aziridines with N,N‐dimethyl‐formamide in the presence of boron trifluoride etherate. Reaction with sodium azide caused some difficulties; complex product mixtures were usually obtained. N‐Sulfonylaziridine‐2‐carboxylic esters gave a mixture of the two possible regioisomers, resulting from attack at C2 and C3. Treatment of N‐sulfonylaziridine‐2‐carboxylic esters with trimethylsilyl azide, however, gave products exclusively ring‐opened at C2. On reaction of the activated aziridines with acetonitrile in the presence of boron trifluoride etherate, a ring‐expansion reaction was observed, leading to imidazolines. On standing, these heterocyclic compounds slowly hydrolyzed to α,β‐diamino carboxylic acid derivatives.
Steric perturbation of the conjugated triene chromophore. Conformational analysis of (E)‐ and (Z)‐3‐methyl‐1,3,5‐hexatriene and (Z)‐3‐tert‐butyl‐1,3,5‐hexatriene
Authors: Brouwer A. M. , Bezemer L. , Jacobs H. J. C.
Published: September 2010

A theoretical and NMR‐spectroscopic conformational analysis is presented of the 3‐methyl‐1,3,5‐hexatrienes and of (Z)‐3‐tert‐butyl‐1,3,5‐hexatriene. It is shown that (E)‐3‐methyl‐1,3,5‐hexatriene exists mainly as the tEt rotamer and (Z)‐3‐methyl‐1,3,5‐hexatriene as the tZt rotamer. Indications are found for steric strain involving the methyl group of the E isomer. In contrast to earlier theoretical predictions, this strain does not lead to detectable amounts of s‐cis rotamers. Ab‐initio calculations reported here agree with this experimental finding, but MMP2 calculations underestimate the energy of the s‐cis form.

1H NMR relaxation rates and Nuclear Overhauser Enhancements (NOE) are shown to allow a reliable determination of the predominant ground‐state conformation of alkyl‐substituted hexatrienes.

NOE experiments on (Z)‐3‐ter‐butyl‐1,3,5‐hexatriene reveal that a tert‐butyl group changes the preferred conformation from tZt to cZt but, surprisingly, is unable to completely counteract the strong intrinsic preference for a spatially extended s‐trans,s‐trans conformation. We estimate the rotamer population as cZt/tZt = 80/20 (± 5).
Near absolute regio‐, diastereo‐, and enantioselectivity in a palladium catalyzed alkylation using an uncommon chiral auxiliary
Authors: Sjouken Ronald , Ebens Rijko , Kellogg Richard M.
Published: September 2010

Condensation of R‐(+)‐1‐(2‐chlorophenyl)‐2,2‐dimethyl‐propan‐1,3‐diol (2) with a derivative (1) of 1‐formylcyclohexene substituted in the 3‐position with an acetoxy group proceeded with absolute stereospecificity at the acetal center. Catalytic alkylation of the π‐allyl complex obtained upon reaction with Pd with the anion of dimethylamalonate proceeded at the 3‐position of the cyclohexyl ring with complete stereocontrol.
Reactions of sulfur trioxide with benzene derivatives containing a deactivating oxy substituent
Authors: Ansink Harold R. W. , Cerfontain Hans
Published: September 2010

The reactions of phenyl acetate (2), (trifluoromethoxy)benzene (3), (difluoromethoxy)‐benzene (4), 4‐(trifluoromethoxy)phenol (5), 4‐(trifluoromethoxy)phenyl methanesulfonate (6), 4‐(trifluoromethoxy)anisole (7) and 3‐(trifluoromethoxy)anisole (8) with SO3, in nitromethane have been studied. Upon reaction with SO3, 2 yields 2‐4‐sulfonic acid (2‐4‐S); subsequently, transfer of the acetyl group takes place to yield the mixed anhydride of phenol‐4‐pyrosulfonic acid and acetic acid (9) or the corresponding hydrogen sulfate 10, depending on the amount of SO3, used. Reaction of the α‐fluorinated anisoles 3 and 4 with SO3 leads to sulfonation at the 4‐position only; however, on using both a high substrate concentration and an excess of SO3, some 2,4‐S2, is formed with 4 but not with 3.

On reaction of 5 with 0.8 mol‐equiv of SO3, in C2H3NO2, the hydrogen sulfate derivative (5‐O‐S) is formed; at 100°C, some isomerization to 5‐2‐S occurs. Upon reaction with 4.0 mol‐equiv of SO3, the initially formed hydrogen sulfate slowly yields the corresponding 2‐sulfophenyl hydrogen sulfate (5‐O,2‐S2). On using 6.0 mol‐equiv of SO3, the 5‐O,2‐S2 is slowly converted into 6‐(trifluoro‐methoxy)benzo‐1,3,2,4‐dioxadithiin 2,2,4,4‐tetraoxide (11). Reaction of 6 with either 0.9 or 3.0 mol‐equiv of SO3, initially leads to insertion of sulfur trioxide in between the SO2CH3, and the adjacent O, yielding the 4‐(trifluoromethoxy)phenyl methanepyrosulfonate 12. This species subsequently yields 13 and 14. Reaction of 7 with SO3 leads to sulfonation only at the 2‐position; eventually some sulfodemethylation to yield 5‐2‐S takes place. Reaction of 8 with 1.0 mol‐equiv of SO3, yields a 68: 32 mixture of 8‐4‐S and 8‐6‐S.
Solid‐phase synthesis of oligodeoxynucleotides containing 6‐O‐alkylguanosines
Authors: Roelen H. C. P. F. , Brugghe H. F. , van den Elst H. , Klein J. C. , van der Marel G. A. , van Boom J. H.
Published: September 2010

High‐quality oligodeoxynucleotides having an 6‐O‐alkyl‐2′‐deoxyguanosine (alkyl = methyl, ethyl, n‐propyl or n‐hexyl) residue at a predetermined position can be obtained via a solid‐phase approach using the respective 2‐cyanoethyl N,N‐diisopropylphosphoramidites of 5′‐O‐(4.4′‐dimethoxytrityl)‐protected 6‐O‐alkyl‐2′‐deoxyguanosines having a free exocyclic amino group, and 5′‐O‐(4‐4′‐dimethoxytrityl) N‐acyl‐protected (i.e., benzoyl and isobutyryl for dC/dA and dG, respectively) 2′‐deoxynucleosides.
Competing concepts in CAOS
Authors: Dengler Alf , Fontain Eric , Knauer Michael , Stein Natalie , Ugi Ivar
Published: September 2010

The evolution of Computer‐Assisted Organic Synthesis (CAOS) is briefly reviewed. The underlying concepts and strategies of the various approaches to CAOS are compared. A status report is given on bilateral synthesis design. This requires selection of suitable starting materials from a list of available compounds according to structural features of the target by correlation of substructures, augmentation of the target molecule by co‐products to yield an Ensemble of Molecules (EM) that is isomeric to the starting EM and, finally, establishment of synthesis routes that lead from the starting EM to the target EM. Despite of its apparent complexity, bilateral CAOS is a promising approach because of its combinatorial advantages.
A collection of computer methods for synthesis design and reaction prediction
Authors: Gasteiger J. , Ihlenfeldt W. D. , Röse P.
Published: September 2010

A series of computer methods is presented that elucidate relationships between the target molecule, precursors, and starting materials of a synthesis. Both retrosynthetic and synthetic searches are performed to find the most rewarding pathways for the synthesis of complex organic structures including their stereochemical features. A user interface has been developed that allows easy switching between the various search methods and the results can be presented graphically. A system for reaction prediction has been developed that can predict the course and products of organic reactions to various depth of chemical knowledge, from the generation of isomers, up to the calculation of absolute rate constants.
Synthesis and characterisation of nitro‐, nitroso‐ and aminofluoranthenes
Authors: van Haeringen C. J. , Aten N. F. , Cornelisse J. , Lugtenbarg J.
Published: September 2010

The synthesis is reported of the five mononitrofluoranthenes. 1‐Nitrofluoranthene was synthesized in 20% from fluoranthene, 2‐nitrofluoranthene in 24% from 1,2,3,10b‐tetrahydrofluoranthene, 3‐nitrofluoranthene in 13% from fluoranthene and 7‐ and 8‐nitrofluoranthene in 34% from 1,2,3,10b‐tetrahydrofluoranthene. The pure nitrofluoranthenes were converted into their nitroso and amino analogues. The nitrosopyrenes were also synthesized. Characterisation of each compound is described.
Diels‐Alder cycloadditions: 3‐(p‐toluenesulfonyl)‐2‐propenal as dienophile
Authors: Riahi Abdelkhalek , Muzart Jacques , Pete Jean‐Pierre
Published: September 2010

The cycloadditions of 3‐(p‐toluenesulfonyl)‐2‐propenal with cyclopentadiene, 1,3‐cyclo‐hexadiene, 1‐methoxy‐1,3‐cyclohexadiene, 1‐(trimethylsilyloxy)‐1,3‐butadiene, or 1,3‐diphenyliso‐benzofuran have been easily carried out at room temperature in the absence of catalyst. In contrast, furan has led to a Michael‐type addition. The basic elimination of the sulfonyl moiety of a cyclo‐adduct has shown that this dienophile is a synthetic equivalent of propynal.
Regioselective ring opening by propanethiolate of (methylenedioxy)benzenes with electron‐withdrawing substituents
Authors: Cassels Bruce K. , Radetski Claudemir , Rezende Marcos Caroli
Published: September 2010

The ring opening reaction of (methylenedioxy)benzenes 1 with propanethiolate in DMF leads to products 2 and/or 3, depending on the nature of the electron‐withdrawing substituent Z.
Reaction of (di)methoxynaphthalenes and 2,3‐(ethylenedioxy)naphthalene with sulfur trioxide
Authors: Ansink Harold R. W. , de Graaf Erik J. , Zelvelder Erwin , Cerfontain Hans
Published: September 2010

The mono‐ and disulfonations of the two methoxynaphthalenes (MON's), nine dimethoxynaphthalenes (DMON's) and 2,3‐(ethylenedioxy)naphthalene (EDN) with sulfur trioxide in mainly nitromethane have been studied. Both the monosulfonations and the disulfonations of the MON's and DMON's in nitromethane lead to one or two products. Steric hindrance caused by the preferred conformation of the methoxy substituent(s) appears to have a strong influence on the substitution pattern. Provided that allowance is made for this specific steric hindrance, the substitution patterns are in agreement with the localization energies, obtained by simple Hückel MO calculations. The positional reactivity orders for the sulfonation of the (D)MON‐monosulfonic acids have been analyzed in terms of (i) the localization energies of the parent compounds, (ii) the (electronic) directing effect of the sulfonic acid substituent and (iii) the difference in steric hindrance for the introduction of the second sulfonic acid group. This analysis suggests that the electronic directing effect of the sulfonic acid group is at most quite small, and is overruled by both the electronic and steric requirements of the methoxy group.
Synthesis and cation complexation selectivity of bis(syn‐proximally) functionalized calix[4]arenes
Authors: Brunink Jos A. J. , Verboom Willem , Engbersen Johan F. J. , Reinhoudt David N. , Harkema Sybolt
Published: September 2010

A general method has been developed for the preparation of bis(syn‐proximally) functionalized calix[4]arenes (6, 8–10). Starting from p‐tert‐butylcalix[4]arene 1a and calix[4]arene 1b syn‐proximally dialkylated calix[4]arenes 2a and 2b, 4, and 5, respectively, were obtained by treatment with 4.2 equiv of NaH and 2.2 equiv of alkylating reagent in DMF. The syn‐proximal substitution pattern was unequivocally proven by an X‐ray structural determination of 2b. Furthermore the influence of different bases on the functionalization of the free hydroxyl groups of 2b with chloroacetone was studied. Cs2CO3 as the base gave the bis(syn‐proximally) functionalized calix[4]‐arene 6 in the highest yield (82%). Cation complexation studies, with the picrate extraction method, showed that subtle changes in regioselective functionalization influences the selectivity for Na4 considerably.
Unusually sluggish copper(I)catalyzed oxidative dimerization of 2‐ethynyl‐1‐methylpyrrole
Authors: Vasilevsky S. F. , Verkruijsse H. D. , Brandsma L.
Published: September 2010

Reaction of 2‐ethynyl‐1‐methylpyrrole with oxygen in the presence of catalytic amounts of copper(I)chloride proceeds only upon addition of 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU).
Synthesis and biological activity of new etorphine analogues from 7‐chloro‐6‐demethoxythebaine and 7‐chloro‐5β‐methyl‐6‐demethoxythebaine (chemistry of opium alkaloids, part XXXVII)
Authors: Woudenberg R. H. , Maat L.
Published: September 2010

The Diels‐Alder reaction of 7‐chloro‐6‐demethoxythebaine (8) and 7‐chloro‐5β‐methyl‐ ‐6‐demethoxythebaine (14) each with ethyl acrylate yielded four (14:6:4:1) and three adducts (15:4:1), respectively. The main adduct from diene 8 was the ethyl 6α,14α‐ethenoisomorphinan‐7α‐ ‐carboxylate 15, while diene 14 afforded the ethyl 6β,14β‐ethenomorphinan‐8β‐carboxylate congener 17 in which the dienophile has reacted from the opposite face. Cycloaddition of 8 and 14 with maleic anhydride, followed by esterification, yielded the 6α,14α‐ethenoisomorphinans 23 and 24, respectively, as the main adducts in both cases. In the case of diene 14 a considerable amount (20%) of the 6β,14β‐ethenomorphinan 25 was also isolated.

The adducts 15, 16, and 19 were 3‐O‐demethylated using boron tribromide to their 3‐hydroxy esters 26, 28, and 30. Conversion of these esters into the tertiary alcohols 27, 29, and 31 was performed using methylmagnesium bromide. Compared to morphine and etorphine, the compounds 26–29 exhibit high affinity for all the opiate receptor subtypes with a higher selectivity for the μ‐receptor. The compounds 30 and 31 were inactive.

The outcome of the cycloadditions is discussed in terms of the electronic influence of the 7‐chloro substituent in the presence or absence of the 5β‐methyl group.
Serotonin agonists and antagonists. Pharmacological tools and therapeutics
Authors: van Wijngaarden I. , Tulp M. Th. M. , Soudijn W.
Published: September 2010

Medicinal chemists have provided crucial tools for the identification and characterization of various subtypes of serotonin (5‐hydroxytryptamine, 5‐HT) receptors. At present, potent and selective (ratio ≥ 100) ligands have been developed for the 5‐HT1A, 5‐HT1Band 5‐HT3receptor subtype. For the 5‐HT1C, 5‐HT1D, 5‐HT1E, 5‐HT2and 5‐HT4receptor subtypes, only potent, non‐selective compounds are available. In this paper, we present the affinities (obtained by radioligand binding studies) of the most selective tools known today for each of the 5‐HT subtypes and we describe some structure‐affinity relationships of a number of interesting compounds. The potential use of several of these selective ligands as pharmacological tools and therapeutics will be briefly reviewed.
A theoretical study on the oxidative metabolism of 4‐chloroacetanilide by cytochrome P450: Alternative mechanisms for migration of 4‐substituents during enzymatic oxidation
Authors: Koymans L. M. H. , Menge W. M. P. B. , Den Kelder G. M. Donné‐Op , Te Koppele J. M. , Vermeulen N. P. E. , van Lenthe J. H.
Published: September 2010

The oxidative metabolism of 4‐chloroacetanilide (4‐ClAA,1) by cytochrome P450 has been studied theoretically usingab‐initioenergy and spin‐distribution calculations. A mechanism of oxidation for 4‐ClAA is proposed which is in accordance with recent views on the mechanism of metabolic oxidation of substrates by cytochrome P450. An initial one‐electron‐oxidation step in the metabolic activation of 4‐ClAA is suggested to be a hydrogen abstraction from nitrogen in the acetylamino side chain. Spin‐delocalisation and subsequent radical recombination reactions between a hydroxyl radical and the reactive centres of the substrate radical can explain the formation ofN‐HO‐ and 2‐HO‐4‐ClAA (4, 9), two known metabolites of 4‐ClAA. Furthermore, the formation of a 2,5‐cyclohexadien‐1‐imine intermediate (6) is proposed. Hypothetical addition‐elimination mechanisms for the decomposition of this intermediate, which are supported by experimental data on analogous compounds, explain the formation of 4‐HOAA, 3‐HO‐4‐ClAA (10), and 3‐Cl‐4‐HOAA (11), three other known metabolites of 4‐ClAA (1).
Sulfonation of a series of naphthalenes containing two different oxy substituents
Authors: Ansink Harold R. W. , Zelvelder Erwin , Cerfontain Hans
Published: September 2010

The reactions of a series of α,α‐ and β,β‐disubstituted naphthalenes containing two different substituents OR1 (R1 = H, SO2CH3) and OR2 (R2 = CH3, SO2CH3) with sulfur trioxide in CD3NO2 has been studied. The electronic directing effect of the hydroxy group was found to be dominant over that of the methoxy group, which in turn dominates that of the mesyloxy group. Upon reaction with an excess of sulfur trioxide, the hydroxy group is, at least in part, sulfated. For the β‐hydroxy‐β‐methoxynaphthalenes 3a–5a and for 3‐mesyloxy‐2‐naphthol (3c) especially, hydrogen sulfate formation strongly influences the product mixture composition. Thus, upon reaction with 1.0 equiv of SO3, 7‐methoxy‐2‐naphthol (5a) yields its 1‐sulfonic acid (1‐S), whereas upon reaction with 2.0 equiv, it is the 8‐S that is mainly formed due to initial hydrogen sulfate formation. Furthermore, sulfonic acid isomerizations due to steric hindrance are observed. Upon using ≥ 2.0 equiv of SO3, formation of di‐ and trisulfonic acids, as well as sulfo derivatives of both 8,1‐naphthalenesultone and the cyclic naphthalene‐1‐sulfonate‐2‐sulfate anhydride is observed.
Intramolecular competition in Friedel‐Crafts sulfocyclization of ω‐(1‐naphthyl)‐n‐alkenes and 1,7‐diphenyl‐3‐heptene on reaction with sulfur trioxide
Authors: Schonk Ruud M. , Lembeck Imelda , Bakker Bert H. , Cerfontain Hans
Published: September 2010

Reactions of the ω‐(1‐naphthyl)‐n‐alkenes 1a–9a and 1,7‐diphenyl‐3‐heptene (10) (substrates which allow intramolecular competition in any occurring sulfocyclization) with sulfur trioxide were studied in the temperature range −60 to 25°C using dichloromethane as solvent and 1.5 mol equiv. of dioxane relative to the amount of SO3 as reactivity moderator. 4‐(1‐Naphthyl)‐1‐butene reacts with SO3, similar to a simple alkene, yielding at low temperature the β‐sultone 1b, which at 25°C in the presence of additional SO3, is converted into the corresponding carbyl sulfate 1d. Reaction of the ω‐(1‐naphthyl)‐n‐alkenes 2a–5a, which have a ‐(CH2)2‐ linkage between the 1‐naphthyl (1‐Np) and C=C moieties, with 1.1 equiv. of SO3, at −60°C yields very rapidly, quantitatively and stereospecifically the 1,2,3,4‐tetrahydro‐1‐alkyl‐phenanthrene‐2‐sulfonic acids 2f–5f. Reaction of the 3‐(1‐naphthyl)‐1‐phenyl‐1‐propenes 8a and 9a, having a ‐CH2‐ linkage between the 1‐Np and C=C moieties, with 1.1 mol equiv. of sulfur trioxide at −60°C quantitatively yields the β‐sultones 8c and 9c, which upon increasing the temperature, are converted into trans‐3‐phenylbenz[g]indane‐2‐sulfonic acid (11). Reaction of 1,7‐diphenyl‐3‐heptene (10) with 1.1 equiv. of SO3, leads to exclusive formation of 1,2,3,4‐tetrahydro‐1‐(3‐phenylpropyl)naphthalene‐2‐sulfonic acid (13). Using ClSO3SiMe3, instead of SO3, the reaction proceeds less selectively and yields, in addition to 3. 18% of 1,2,3,4‐tetrahydro‐1‐(3‐phenyl‐1‐sulfopropyl)naphthalene (14). Mechanisms for the formation of the various products are suggested and the observed selectivity in the sulfocyclizations are discussed.
Synthesis and spectroscopy of nitroaceanthrylenes and nitroaceanthrenes
Authors: Mulder Patrick P. J. , Boerrigter Jos Olde , Boere Ben B. , Zuilhof Han , Erkelens Cornelis , Cornelisse Jan , Lugtenburg Johan
Published: September 2010

The syntheses of nine mononitro derivatives of aceanthrylene (1) and nine mononitro derivatives of aceanthrene (2) are described. In addition to 1 and 2, 1,2,6,10b‐tetrahydroaceanthrylene (3), 6,10b‐dihydro‐2(1H)‐aceanthrylenone (5), 1(2H)‐aceanthrylenone (4) and 2(1H)‐aceanthrylenone (8) were also used as starting materials. The resulting nitroaceanthrylenes and nitroaceanthrenes were characterized by their 1H‐NMR, 13C‐NMR, UV‐VIS, IR and mass spectra. The conformation of the nitro group and the interaction between the nitro group and the aromatic system are discussed. In 2‐nitroaceanthrylene (1b), the nitro group interacts exceptionally well with the aromatic nucleus. The 3‐, 4‐, 8‐ and 9‐nitro derivatives of 1 and 2 display all the characteristics of normally conjugated planar nitroaromatic compounds. In the remaining nitro derivatives of 1 and 2, conjugation is diminished owing to steric interactions with nearby protons. The order of decreasing conjugation and increasing twist angle is 5‐nitro > 7‐nitro > 6‐nitro > 10‐nitro. The twist angle of the nitro group was calculated using semi‐empirical SCF methods PM3 and AM1. Although the values obtained by these methods deviate substantially, they both give the same order of increasing twist angles as the spectroscopically derived order.
α, ω‐Dipolar amphiphiles: Influence of rigid and flexible units on aggregation behavior
Authors: Hessel V. , Ringsdorf H. , Laversanne R. , Nallet F.
Published: September 2010

Mono‐ and α,ω‐dipolar amphiphiles with hydrophilic pyridinium head groups, and flexible and rigid hydrophobic parts have been synthesized. Surface tension and conductivity measurements proved that micellar aggregates for amphiphiles 1–4 are formed. The incorporation of rigid units leads to a decrease in the critical micellar concentration (CMC): the rigid monopolar amphiphile 2 aggregates at lower concentration than the flexible monopolar amphiphile 1. A similar decrease was observed when chain ends were connected: the flexible α,ω‐dipolar amphiphile 3 has a lower CMC than the flexible monopolar amphiphile 1. The more flexible amphiphiles 1–3 allow the formation of micelles of different shape leading to both CMC and Ct values. For the α,ω‐dipolar amphiphile 4 with a rigid azoxybiphenylene core, the possibility of different micellar shapes is reduced, leading only to a CMC value (CMC = Ct). For the flexible α,ω‐dipolar amphiphile 3, only a small, but linear viscosity increase with concentration is found. Very viscous solutions were measured for the rigid α,ω‐dipolar amphiphile 4 above a certain concentration. Phase diagrams of amphiphiles 3 and 4 were determined using polarization‐microscopy and X‐ray measurements. Flexible α,ω‐dipolar amphiphile 3 shows a lyotropic mesophase only at very high concentration (83 mass %). In contrast, rigid analog 4 forms stable lyotropic mesophases at 16 mass %. Both nematic and higher ordered mesophases (probably lamellar) are found for the rigid α,ω‐dipolar amphiphile 4.
Catalytic hydrolysis of phosphate esters by metallocomplexes of 1,10‐phenanthroline derivatives in micellar solution
Authors: Weijnen John G. J. , Engbersen Johan F. J.
Published: September 2010

Divalent metal‐ion complexes of 2,9‐bis[(methyldodecylamino)methyl]‐1,10‐phenanthroline (C12PhenMII) in neutral Brij 35 micelles catalyse the hydrolysis of various phosphate triesters, diesters and monoesters. The catalytic activity of C12PhenMII has been compared with that of the metal‐ion complexes of its water‐soluble counterpart 2,9‐bis[(dimethyl‐amino)methyl]‐1,10‐phenanthroline (C1PhenMII). Saturation kinetics provide evidence for preliminary formation of ligand‐MII‐phosphate ester complexes, which decay to products. The hydrolysis of diphenyl 4‐nitrophenyl phosphate (1b) coordinated to C12PhenZnII proceeds 8700 times faster than the hydrolysis of 1b in the absence of metallocatalyst. Kinetic studies indicate that phosphate triesters containing a metal‐ion‐binding site in close proximity to the phosphoryl bond, i.e., diphenyl 5‐nitro‐2‐pyridyl phosphate (2b) and diphenyl 5‐nitro‐8‐quinolyl phosphate (3), are hydrolysed by the same mechanism as 1b.
New water‐soluble calixarenes modified with amino acids at the upper rim
Authors: Nagasaki Takeshi , Tajiri Yusuke , Shinkai Seiji
Published: September 2010

Calix[n]arenes (n = 4 and 6) modified with L‐cysteines were synthesized. These calix[n]arenes were water‐soluble, particularly, at acidic and basic pH regions. The critical micelle concentrations (estimated by surface tension) appeared at (0.50‐3.2) · 10−5 M. The “hydrophobicity” of these cavities was estimated by fluorescence of 8‐anilino‐1‐naphthalene‐sulfonate (ANS): it showed that these calix[n]arenes become most hydrophobic at pH 5‐6. The selectivity in guest inclusion was significantly affected by the medium pH.
Reactions of methylenecycloalkanes and cycloalkylidenecycloalkanes with sulfur trioxide
Authors: Schonk Ruud M. , Meijer Carel W. , Bakker Bert H. , Cerfontain Hans , Zöllner Stephan , de Meijere Armin
Published: September 2010

Reactions of methylenecycloalkanes 1a‐4a and cycloalkylidenecycloalkanes 11a–14a with sulfur trioxide were studied in the temperature range −60 to 25°C using dichloromethane as solvent and 1.5 mol equiv. of dioxane relative to the amount of SO3 as reactivity moderator. Methylenecyclooctane (1a), methylenecyclohexane (2a) and methylenecylopentane (3a) react with SO3 just like simple branched alkenes yielding quantitatively the corresponding β‐alkenesulfonic acids 1d‐3d. Reaction of methylenecyclobutane (4a) with 1.0 equiv. of SO3 at −60°C yields the β‐sultone 4b, which upon raising the temperature to 0°C, rearranges into γ‐sultone 6 and subsequently, slowly into δ‐sultone 9. Sulfonation of the cycloalkylidenecycloalkanes 11a‐13a with 1.0 equiv. of SO3 at −60°C leads to quantitative formation of the spiro‐β‐sultones 11b‐13b, respectively. After raising the temperature, these β‐sultones are converted into the corresponding β‐alkenesulfonic acids 11d‐13d, which are common reaction products in sulfonation of tetraalkylethenes.

Sulfonation of cyclopropylidenecyclopropane (14a) with SO3 at −60°C proceeds with rearrangement of one of the cyclopropyl groups to give quantitatively the spirocyclopropane‐γ‐sultone 15. Mechanisms for the formation of the various products are discussed.
Selective oxidation of penicillin G with hydrogen peroxide and with enzymatically generated peroxyoctanoic acid
Authors: de Zoete M. C. , van Rantwijk F. , Maat L. , Sheldon R. A.
Published: September 2010

Two convenient procedures for the oxidation of penicillin G into penicillin G 1‐(s)‐oxide have been developed. Both the mild oxidation with enzymatically generated peroxyoctanoic acid and the attractive and simple oxidation with the sole use of hydrogen peroxide are valuable alternatives for the commercial oxidation with 40% peroxyacetic acid.
Functionalized binaphthyl salophen crown ethers as models for the enzyme urease
Authors: Reichwein Arjen M. , Verboom Willem , Reinhoudt David N.
Published: September 2010

Functionalized binaphthyl salophen crown ethers 2 and 3 containing a Lewis‐acidic uranyl cation were prepared by the Ba2+‐templated cyclization of dialdehydes 15 and 22, for which two convenient synthetic routes were developed, with diamines 23 and 24. Intramolecular complexation of the amide groups in metallomacrocycles 2 and 3 was demonstrated by the isolation of two different forms of 2a, which were observed to interconvert, by 1H‐NMR and IR spectroscopy and by electrochemical measurements. Use of diamine 24 during the cyclization resulted in the formation of two different stereoisomers of the monofunctionalized metallomacrocycles 3a‐d and in “sidedness” of the bisfunctionalized metallomacrocycles 3e and 3f. Solid complexes of urea and 2c and 2d were isolated, but no catalytic activity was observed for 2a in the hydrolysis of urea in dioxane / water.
A stereospecific anionic reduction of gem‐bromohalocyclopropanes by the dimsyl anion
Authors: Wijsman G. W. , de Wolf W. H. , Bickelhaupt F.
Published: September 2010

The reaction of several 2,2,3,3‐tetrasubstituted‐gem‐bromohalocyclopropanes with t‐BuOK in DMSO unexpectedly yielded the monohalocyclopropanes in good yield. A closer investigation revealed that this reaction must be initiated by a nucleophilic attack by the dimsyl anion (CH3SOCH3) on bromine with subsequent protonation of the carbenoid intermediate. The reaction occurs rapidly (within 2 minutes) and is not inhibited by radical scavengers or in the dark. Only bromine, and not chlorine, is reduced, and the intermediate cyclopropyl anion is configurationally stable under the reaction conditions.
Highly selective tempo mediated oxidation of primary alcohol groups in polysaccharides
Authors: de Nooy A.E.J. , Besemer A.C. , van Bekkum H.
Published: September 2010

A method for the selective oxidation of the primary hydroxyl functions of polysaccharides is described. The oxidation is mediated by 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) and hypobromite is used as the regenerating oxidant. At pH 10.5–11 a selectivity of 98% for cold water soluble potato starch and >90% for dahlia inulin was found.
Head‐group conformations in lipid bilayer membranes
Authors: Meijer L.A. , Leermakers F.A.M. , Lyklema J.
Published: September 2010

The self‐assembly of lipid molecules into lamellar liquid‐crystalline bilayer membranes was studied using a statistical thermodynamic method elaborating a Scheutjens‐Fleer‐like approach. In the modelling much attention was paid to the two‐tail character and the complex head‐group structure of the lipids that comprise the bilayer.

Zwitterionic head groups like phosphatidylcholine (PC) are, on average, oriented nearly flat onto the interface. At not too low ionic strengths, we find that the PC head group has two preferred conformations. Ionic head groups like phosphatidylserine (PS) are tilted towards the solution. These two predictions are consistent with experimental data.

Both co‐ and counter‐ions penetrate the head‐group region, compensating for part of the head‐group charges. Usually the counter‐ions adsorb preferentially. However, at high salt concentrations, no positive adsorption of ions is found in dimyristoylphosphatidylserine (DMPS) bilayers. Due to the lateral pressure in the head‐group area, all ions are depleted. Since negative ions are more depleted than positive ones, charge compensation is still achieved.

In order to investigate how the membrane structure can be modulated, we modified the lipids by adding a hydrophilic chain onto the end of the PC head group. There are two effects. First, the increase of the bulkiness of the head group reduces the number of lipids per unit area in the membrane so that the size of the hydrophobic core diminishes. Second, we predict that the orientation of the PC part of the head group is altered non‐monotonically. Increasing the electrostatic screening promotes the out‐of‐plane tilting of the head groups toward entropically more favourable positions.
Models of micelle formation
Authors: van Os N.M. , Smit B. , Karaborni S.
Published: September 2010

We have tested the predictions of four thermodynamic models of micelle formation against experimental enthalpies of micelle formation of model surfactants across a range of temperatures. The mass action (MA) approach agrees best with experimental observations.

The change in thermodynamic parameters of micelle formation with temperature has been interpreted according to a two‐step model of hydrogen bonds in water. This model explains the trends correctly but is open to criticism regarding the choice of parameters.

We give a brief review of our own computer simulations of self‐assembly which suggest that non‐hydrogen‐bonded liquids are solvents in which self‐assembly can take place too. Other experimental evidence lends support to the conclusion that a sufficiently large difference between the solvent and solute cohesiveness parameters is enough for self‐assembly to occur in a solvent.
C‐Halophosphaalkenes: Probing the range of stability and reactivity towards bromine
Authors: Goede S.J. , Dam M.A. , Bickelhaupt F.
Published: September 2010

The importance of steric protection for the stability of phosphaalkenes RP=CI2 (6) was investigated by varying the size of group R. The phosphaalkene IsP=CI2 (6b) (Is = 2,4,6‐triisopropylphenyl) could be prepared in 15% isolated yield by reaction of IsPCl2 and HCI3 with two equivalents of lithium diisopropylamide, in analogy to the synthesis of the stable, sterically more protected, Mes*P = CI2 (6a) (Mes* = 2,4,6‐tri‐tert‐butylphenyl). If the steric protection on the phosphorus was decreased further (R = Es = 2,4,6‐triethylphenyl, R = Mes = 2,4,6‐trimethylphenyl), the substitution products RP(Cl)N(Pri)2 (R = Es (9c) or Mes (9d)) were formed as main products, in addition to thermally unstable phosphaalkenes EsP=CI2 (6c) and MesP=CI2 (6d). The structures of 9c‐d were corroborated by independent synthesis from RPCl2 and two equivalents of diisopropylamine.

The reaction of 6awith bromine gave an E/Z mixture of the C‐bromo‐C‐iodophosphaalkene (EZ)‐Mes* P = CBrI (E/Z‐10). Further reaction with bromine proceeded via Mes*P=CBr2 (5a) and finally led to Mes* P(Br)(CHBr2) (12).
Synthesis of and vesicle formation from phosphorylcholine amphiphiles with one symmetrically branched alkyl chain
Authors: Overmars Franc J. J. , Engberts Jan B. F. N. , Weringa Wilke D.
Published: September 2010

Three phosphorylcholines with symmetrically branched alkyl chains [(CnH2n + 1)2 CHOPO3−(CH2)2N(CH3)3+] (1a‐c) have been synthesized. The synthesis involves three steps: (1) reaction of the alcohol (CnH2n + 1)2CHOH, (n = 6, 8, 10) with 2‐chloro‐1,3,2‐dioxaphospholane in the presence of triethylamine; (2) oxidation of the resulting trialkyl phosphite with nitrogen dioxide and (3) ring opening of the cyclic phosphate triester by trimethylamine in acetonitrile. When suspended in water, these amphiphiles all form bilayer vesicles as revealed by electron microscopy and NMR spectroscopy. The vesicles have diameters of 300‐1000 Å and are stable for more than a week.
Enzymatic synthesis of specifically 2H‐labelled L‐glutamic acids and 2H‐, 15N‐, 13C‐labelled L‐glutamines on a preparative scale
Authors: Ogrel A. , Vasilenko I. A. , Lugtenburg J. , Raap J.
Published: September 2010

In this paper we report the preparation of specifically 2H‐labelled L‐glutamic acids and 2H‐, 15N‐, 13C‐labelled L‐glutamines on the gram scale. The products obtained have high isotope enrichment (>98%) and high optical purity. The synthetic schemes allow the specific isotope enrichment of every H, C, and N position or any combination of positions. (2‐2H)‐L‐Glutamic acid was synthesized by enantioselective enzymatic conversion of 2‐oxoglutaric acid using glutamate dehydrogenase (GDH, E.C. 1.4.1.3.), alcohol dehydrogenase (ADH, E.C. 1.1.1.1.) and (2H6)ethanol. (3,3‐2H2)‐L‐Glutamic acid was prepared by enzymatic conversion of 2‐oxo‐3,3‐di‐deuteroglutaric acid which was easily obtained from 2‐oxoglutaric acid by an isotope exchange reaction in 2H2O at pH 13.0. (4,4‐2H2)‐L‐Glutamic acid was obtained by chemical exchange in 20% 2HCl. Four different isotopomers of L‐glutamine [(2‐2H)‐, (3,3‐2H2)‐, (4,4‐2H2)‐, and (5‐13C)‐L‐Gln] were synthesized by the enantioselective conversion of isotopically labelled L‐glutamic acids using glutamine synthetase (GS, E.C. 6.3.1.2.). The amide group of glutamine was labelled with 15N using 15NH4Cl in the enzymatic reaction. The labelled L‐glutamic acids and L‐glutamines were characterized by 1H‐NMR, 13C‐NMR and mass spectrometry.
Dramatic acceleration of alkylation reactions with organolithium compounds by potassium tert‐butoxide
Authors: Brandsma L. , Mal'kina A.G. , Lochmann L. , Schleyer P. Von R.
Published: September 2010

Reactions of organolithium compounds with alkyl halides and with epoxides are considerably accelerated by addition of equivalent amounts of potassium tert‐butoxide.
Synthesis and characterization of all‐E (12,12′‐13C2)‐, (13,13′‐13C2)‐, (14,14′‐13C2)‐, (15,15′‐13C2)‐ and (20,20′‐13C2)astaxanthin
Authors: Jansen F.J.H.M. , Kwestro M. , Schmitt D. , Lugtenburg J.
Published: September 2010

The all‐E isomers of (12,12′‐13C2)‐, (13,13′‐13C2)‐, (14,14′‐13C2)‐, (15,15′‐13C2)‐ and (20,20′‐13C2)astaxanthin were prepared by total synthesis starting from commercially available 99% 13C‐enriched acetonitrile, acetic acid and methyl iodide. The astaxanthins were obtained in high purity and with high isotope incorporation (> 99% for every position). For this synthesis, the C15 + C10 + C15 strategy was used. The central C10‐synthon, 2,7‐dimethylocta‐2,4,6‐triene‐1,8‐dial, was symmetrically dilabelled at any position using two new synthetic schemes. The 13C2‐enriched C10‐dialdehydes were then converted in one step to the 13C2‐enriched astaxanthins.
A novel approach towards the synthesis of pyrophosphate analogues of farnesyl pyrophosphate
Authors: Valentijn A.R.P.M. , van den Berg O. , van der Marel G.A. , van Boom J.H. , Cohen L.H.
Published: September 2010

The synthesis of two new analogues (i.e. 3 and 4) of farnesyl pyrophosphate (FPP) containing a phosphonophosphate and a phosphonophosphonate moiety was accomplished via the phosphonomorpholidate. The latter was easily obtained by treatment of a phosphonic chloride with morpholine.
A quick method for making liquid ammonia super‐dry
Authors: Brandsma L.
Published: September 2010

Liquid ammonia directly drawn from a cylinder can be made super‐dry by alternating, portion‐wise, addition of potassium and t‐butyl chloride, using trace amounts of triphenylmethane as an indicator.
Synthesis of chiral sulfines by oxidation of dithio esters
Authors: van der Linden Johannes B. , Timmermans Johan L. , Zwanenburg Binne
Published: September 2010

The synthesis of sulfines (thione oxides) (2, 10 and 17) derived from three chiral dithio esters (1, 8 and 16) bearing a hydrogen at the α‐carbon atom is described. The sulfine bearing an amido group at C‐α (2), does not racemize and proved to be stable over a long period. When C‐α in the sulfine (10) bears an acetoxy group the optical activity remained unchanged for a period of two months; after longer storage a rearrangement to a mixture of dithioperoxy ester 12 and S‐methyl ester 11 took place. With an alkyl group at C‐α, the sulfine 17 undergoes a fast racemization and rearranges slowly to a mixture of S‐ethyl ester 14, dithioperoxy ester 18 and S‐vinyl thiosulfinate 19.
Synthesis of potential receptor molecules by combination of upper‐rim‐functionalized calix[4]arenes and partly bridged resorcinarenes
Authors: Timmerman Peter , Boerrigter Harold , Verboom Willem , Reinhoudt David N.
Published: September 2010

Combination of upper‐rim‐1,3‐difunctionalized calix[4]arenes 14, 16, and 18 with tribridged resorcinarenes 4 and 6 and A,C‐di‐bridged resorcinarenes 10 and 13 yields both 1/1 calix‐resorcinarenes (22–24) and 2/1 calix‐resorcinarenes (25, 26). 1/1 Calix‐resorcinarene 22 mainly exists as one conformer (a), but at low temperatures (−60°C) very small amounts ( < 5%) of a second conformer (b) can be observed. Both conformers equilibrate via rotation about one of the C(arene)‐N bonds, with an activation free energy (Δ G≠) of 13 kcal/mol. 2/1 Calix‐resorcinarenes 25 and 26 are more flexible and exist as a mixture of conformers. In order to be able to rigidify the structure of 2/1 calix‐resorcinarenes via rigid spacers between the calix[4]arene fragments, 1,3‐diaminocalix[4]arene derivatives 31, 32, and 34 were synthesized carrying nitro, carboxylic ester, and cyano groups at the unsubstituted aromatic rings. With these calix[4]arene derivatives, three new, functionalized 2/1 calix‐resorcinarenes 35–37 have been synthesized.
Syn‐Stereocontrolled dihydroxylation of Baylis‐Hillman adducts
Authors: Markó István E. , Giles Paul R. , Janousek Zdenek , Hindley Nigel J. , Declercq Jean‐Paul , Tinant Bernard , Feneau‐Dupont Janine , Svendsen John S.
Published: September 2010

The hydroxylation of Baylis‐Hillman adducts 1 is shown to proceed with high levels of diastereocontrol. A mechanistic rationale to explain this selectivity is discussed.
Ruthenium diphosphine complexes for catalysis; a general synthesis and direct comparisons with rhodium complexes
Authors: Brown John M. , Rose Michael , Knight Frances I. , Wienand Anette
Published: September 2010

A method for the preparation of diphosphineruthenium complexes from a range of diphosphine precursors is described. The stable products, of general formula P2Ru(allyl)acac (P = phosphine ligand), do not catalyse the hydrogenation of alkenes but can easily be converted into catalytically active species by reaction with trimethylsilyl trifluoromethanesulfonate. The chemistry involved in this transformation is discussed. Catalysis of the hydrogenation of a range of alkenes, and direct comparison with related rhodium reductions, is described. Some mechanistic insights are gained through additions of D2 to alkenes and parallel hydrogenations on deuterated solvent, supporting the intervention of conventional dihydride and alkyl hydride intermediates which undergo exchange with solvent at both stages.
A new chiral solvating agent for carboxylic acids based on directed hydrogen bonding
Authors: Stork Thomas , Helmchen Günter
Published: September 2010

Readily available structural modules were combined to a new chiral receptor for carboxylic acids which shows triple hydrogen‐bonding to various substrates. Large chemical shift anisochronies were observed with chiral and prochiral carboxylic acids.
Inversion of enantioselectivity of serine proteases
Authors: Broos Jaap , Engbersen Johan F. J. , Verboom Willem , Reinhoudt David N.
Published: September 2010

The enantioselectivity of serine proteases in the transesterification of N‐acetyl‐(D,L)‐ phenylalanine esters with propan‐1‐ol in cyclohexane is strongly influenced by the leaving ability of the alcoholate group. Moreover the enantioselectivity is greatly influenced by the addition of small amounts (0.33 M) of organic additives. Addenda with a small molecular volume like e.g. ethanol and acetonitrile increase the rate for the L‐enantiomer whereas alcohols with bulky alkyl groups like e.g. tert‐butanol and 2‐methylbutan‐2‐ol enhance the activity of the enzyme towards the D‐enantiomer. This enables a rational tuning of the enantioselectivity as was demonstrated for four different proteases (α‐chymotrypsin, subtilisin Carlsberg, Aspergillus oryzae protease, and elastase).
Synthesis of new macrocyclic ligands for hetero‐multinuclear transition‐metal complexes
Authors: Huck Wilhelm T. S. , van Veggel Frank C. J. M. , Reinhoudt David N.
Published: September 2010

The [3 + 3] macrocyclic compounds 2a–2c were easily prepared by cyclization of the dialdehyde 8 with the appropiate diamines in refluxing CH3CN/MeOH (1/1), in the presence of Ba2+ as a template ion. These macrocycles contain three salen units and are therefore, in combination with the crown ether interior, potentially tetranucleating. The length of the diamine bridge and the temperature at which the reaction is carried out, appear to influence the size of the macrocycle formed. In this way, the [4 + 4] macrocycle 2d could be formed selectively over the [3 + 3] macrocycles by carrying out the reaction at room temperature.
Metal ion induced disintegration of a pyrazole‐containing ligand and formation of an unprecedented pyrazolato‐bridged di‐zinc anion. The X‐ray structure of the mixed ligand compound bis [(1,6‐bis(3,5‐dimethylpyrazol‐1‐yl)‐2,5‐dimethyl‐2,5‐diazahexane)‐(chloro)zinc(chloro) zinc(II)] [bis(μ‐3,5‐dimethylpyrazolato) tetrachlorodizincaat(II)], [Zn(C16H28N6)Cl]2[Zn2(C5H7N2)2Cl4]
Authors: Driessen W. L. , Paap F. , Reedijk J.
Published: September 2010

The ligand 1,6‐bis(3,5‐dimethylpyrazol‐1‐yl)‐2,5‐dimethyl‐2,5‐diazahexane (debd), which has been synthesized from 3,5‐dimethylpyrazole, N,N′‐dimethylethanediamine and formaldehyde, partially disintegrates when reacted with zinc dichloride or with zinc dibromide in methanol. The resulting compounds contain the unique bis(pyrazolato)‐bridged tetrahalogenido dizinc(II) anion. The compound [Zn(debd)Cl]2[Zn2(dmpz)2Cl4], with formula C42H70Cl6N16Zn4 and Mr = 1273.36, is obtained from methanol as monoclinic crystals, spacegroup P 21/c with a = 15.990(2) Å, b = 16.394(2) Å, c = 12.006(1) Å, β = 100.61(1)°, V = 3093.4(5) Å3, Zm = 2, Dx = 1.37 g.cm−3, as measured at room temperature with Mo(Kα) radiation to a final R value of 0.062 (wR = 0.065) for 2465 significant [I > 2σ‐(I)] reflections.

The asymmetric unit comprises half the formula unit. The cation consists of a Zn2+ ion in a distorted trigonal bipyramidal environment of a chloride ion at 2.221(3) Å, an amine nitrogen at 2.17(1) Å and a pyrazole nitrogen at 2.05(1) Å in the equatorial plane, with an amine nitrogen at 2.27(1) and a pyrazole nitrogen at 2.14(1) Å in the axial positions. The largest distortion is in the axis of the trigonal bipyramide with an N‐Zn‐N angle of 150.2(5)°.

The anion consists of two Zn2+ ions, which are bridged by two deprotonated

The authors realise that the recommended IUPAC term is (de)hydronated instead of (de)protonated to indicate loss/addition of H+.

dimethylpyrazole ligands with N‐Zn distances of 1.97(1) and 1.98(1) Å, while each Zn2+ ion is further bound to two chloride ions at 2.276(4) and 2.261(4) Å. The Zn2+ ions are in an almost regular N2Cl2 tetrahedron.
Reactions of cyclic nitrones with (E)‐γ‐hydroxy‐ and (E)‐γ‐alkoxy‐α,β‐unsaturated esters
Authors: de March P. , Figueredo M. , Font J. , Monsalvatje M.
Published: September 2010

The 1,3‐dipolar cycloadditions of 2,3,4,5‐tetrahydropyridine 1‐oxide (1) and 3,4‐dihydro‐2H‐pyrrole 1‐oxide (2) to methyl (E)‐6‐(benzyloxy)‐4‐hydroxy‐2‐hexenoate (3) and methyl (S)‐(E)‐3‐(2,2‐dimethyl‐1,3‐dioxolan‐4‐yl)propenoate (4) yield predominantly the adducts derived from endo transition states with antifacial approaches.
Intellectual property protection and the formation of entrepreneurial growth aspirations
Authors: Autio Erkko , Acs Zoltan
Published: September 2010

Applying real options logic, we build and test a multilevel model that explicates the influence of a country's intellectual property protection regime on the effect of an individual's human and financial capital on entrepreneurial growth aspirations. The results suggest that the strength of the intellectual property regime moderates negatively the relationship between an individual's education and entrepreneurial growth aspirations; and it moderates positively the relationship between an individual's household income and growth aspirations. Intellectual property protection, thereby, encourages specialization amongst differently qualified entrepreneurs. Our findings support claims that strategic entrepreneurial behaviors cannot be fully understood without giving attention to the context in which those behaviors are observed. Copyright © 2010 Strategic Management Society.