bluuebunny/crossref_metadata_2025 huggingface dataset:
Asymmetric synthesis of α,β‐epoxysulphonate esters (oxiranesulphonate esters)
Authors: Nkunya M. H. H. , Zwanenburg B.
Published: September 2010

The asymmetric phase‐transfer‐catalysed Darzens condensation of aldehydes and ketones with the chiral reagent L‐menthyl chloromethanesulphonate, using triethylbenzylammonium chloride (TEBA) as the phase‐transfer catalyst to give α,β‐epoxysulphonate esters (oxiranesulphonate esters) in 9–17% chiral induction, is described. The stereochemical course of the chiral induction is discussed.
Asymmetric induction in the addition of thioacetic S‐acid to α,β‐unsaturated esters
Authors: Gawroński Jacek K. , Gawrońska Krystyna , Kolbon Halina , Wynberg Hans
Published: September 2010

2‐Methylpropenoates and cis‐ or trans‐butenedioates add thioacetic S‐acid under conditions of asymmetric catalysis by cinchona alkaloids to give optically active thioacetates. Structural factors influencing the stereochemical outcome of the reaction are discussed.
Photochemical reactions of some aromatic thiones with bis(methylthio)ethyne; (4 + 2)‐ versus (2 + 2)‐cycloaddition products. Spectroscopic evidence for the equilibrium thiete ⇄ α,β‐unsaturated dithioester
Authors: Brouwer A. C. , Bos H. J. T.
Published: September 2010

Irradiation (λ > 525 nm) of the aromatic thiones 2 in the presence of bis(methylthio)ethyne 3 causes two cycloaddition reactions to occur between the photochemically excited thione 2 and the acetylene 3, as concluded from the isolated products. Compounds with structure 6 are believed to be products of a (4 + 2)‐cycloaddition reaction, whereas the formation of the isolated α,β‐unsaturated dithio esters 4 is rationalised on the basis of a (2 + 2)‐cycloaddition reaction. The preference for one reaction pathway over the other depends on the thione used and is discussed in terms of the structure of the thione 2. Spectroscopic observation of the equilibrium thiete 5 ⇌ α,β‐unsaturated dithio ester 4, in solution provides direct evidence for the (2 + 2)‐photocycloadducts, thietes 5.
Synthesis of α,β‐unsaturated sulfines from silylindenes and sulfur dioxide
Authors: Porskamp P. A. T. W. , van de Wijdeven A. M. , Zwanenburg B.
Published: September 2010

The synthesis of a variety of substituted indenethione S‐oxides (all α,β‐unsaturated sulfines) is described. Essentially these sulfines are prepared by the reaction of α‐silyl carbanions with an excess of sulfur dioxide (modified Peterson reaction). The requisite α‐silyl carbanions are generated by two different routes, i.e. by α‐deprotonation of trimethylsilyl‐substituted indenes and by nucleophilic δ‐addition of alkyllithium compounds to dienesilanes. In all cases, the sulfines prepared were converted into cycloadducts by reaction with 2,3‐dimethyl‐1,3‐butadiene.
Water‐ and hydroxide‐ion‐catalyzed hydrolysis of 1‐acyl‐1,2,4‐triazoles in mixed aqueous solvents. The effect of substrate hydrophobicity
Authors: Karzijn Willem , Engberts Jan. B. F. N.
Published: September 2010

The solvent dependence of the enthalpies and entropies of activation for the title reactions in water‐rich t‐BuOH‐H2O responds to the hydrophobicity of the substrate.
Synthesis of a teichoic acid fragment of Bacillus subtilis using a modified phosphotriester approach
Authors: van Boeckel C. A. A. , Visser G. M. , Hermans J. P. G. , van Boom J. H.
Published: September 2010

The synthesis of a teichoic acid fragment (i.e. compound 8e), containing three 3‐O–(β‐glucopyranosyl)‐sn‐glycerol residues connected via two phosphodiester linkages, is described. The assemblage of the teichoic acid fragment was effected using a modified phosphotriester approach based on the use of 1‐hydroxybenzotriazole‐activated phosphorylating agents (i.e. phosphorylating agents 5c and 6c). Three suitably protected building blocks were prepared: i.e., 2b, 3c and 4b. Special attention was paid to the preparation of the middle unit 3c which contains a stable phosphodiester anilidate to avoid intramolecular reaction of the free hydroxyl function on phosphorus. Compound 2b was condensed with derivative 3c to give fragment 7a. The aniline group could be removed from dimer 7a to give 7b, which was then condensed with monomer 4b to give the fully protected teichoic acid fragment 8a. Stepwise removal of the protecting group of 8a afforded the teichoic acid fragment 8e.
The decomposition of ethyl diazoacetate over zeolite NaCuX
Authors: Oudejans J. C. , Kaminska J. , van Bekkum H.
Published: September 2010

The decomposition of ethyl diazoacetate catalyzed by Cu(II)‐exchanged zeolite NaX, has been studied. Catalytic activity required at least 25% sodium exchange of the zeolite. From 25% exchange to higher exchange levels the decomposition rate increased linearly with the copper introduced into the zeolite. With cyclohexane as the solvent, the (ethoxycarbonyl)carbene formed was found to yield dimers, diethyl maleate and diethyl fumarate, and also compounds resulting from reaction with the solvent or with residual water present in the zeolite. Reduction of Cu(II) to Cu(I) increased the activity of the catalysts. The degree of hydration of the zeolite had a large effect on the activity of the catalyst and on the selectivity of the reaction. Complexation of the Cu(II) ions with NH3 or 1,2‐propanediamine reduced the activity of the zeolite drastically. Zeolite NaCuX showed no induction time in contrast to several copper salts tested.
Préparation d'un homologue de la PAP
Authors: Daunis J. , Elmahi M. , Ismaili H. , Jacquier R. , Calas B. , Parello J.
Published: September 2010

A non‐statistical analogue of PAP, [poly(N‐acryloylpyrrolidine)], which can be used in peptide synthesis, is easily prepared by reaction of hexanediamine on chemically inert polyacrylic resin. It is shown that its functionalisation number depends upon the degree of cross‐linking in the chemically starting inert resin; swelling properties are slightly dependent upon the nature of the substituents present in the base acrylamide unit.
Chiral base catalysis in the reaction of thiols with a quinone epoxide
Authors: Pluim Henk , Wynberg Hans
Published: September 2010

When p‐tert‐butylbenzenethiol is allowed to react with 2,3‐dimethyl‐1,4‐naphthoquinone 2,3‐epoxide in toluene in the presence of a cinchona alkaloid (e.g. cinchonidine) as catalyst, the ring‐opened β‐hydroxy sulfide is formed in optically active form (ee 65%). The reaction is a model for a biosynthetic step in the Vitamin K function.
Negative ion/molecule cycloaddition reactions of 2‐methylpropenal in the gas phase
Authors: Kleingeld J. C. , Nibbering N. M. M.
Published: September 2010

The gas‐phase negative‐ion chemistry of 2‐methylpropenal has been studied by Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICR). Deuterium labelling has shown that the gas‐phase acidities of the methyl protons and the formyl proton are almost equal. The gas‐phase reactions of the 2‐formylallyl anion with several fluorinated substrates have been shown to proceed mainly via a cycloaddition mechanism.
Synthesis of [L‐m‐Tyr1]‐ and [D‐m‐Tyr1]‐leucine‐enkephalin via the REMA method
Authors: van den Braken‐Van Leersum A. M. , Maat L.
Published: September 2010

The synthesis by the all‐repetitive‐excess‐mixed‐anhydride (REMA) method is described for two analogues of leucine‐enkephalin, viz. [L‐m‐Tyr1]‐ and [D‐m‐Tyr1]‐leucine‐enkephalin, making use of enzymatically resolved (m‐hydroxyphenyl)alanine (m‐tyrosine).
Molecular aspects of methylated adenine in DNA. A quantum‐chemical study
Authors: van Lier Johan J. C. , Stroucken Jacques H. M. , Buck Henk M.
Published: September 2010

On the basis of modified neglect of differential overlap (MNDO) quantum‐chemical calculations on nucleoside systems, the effect of methylation of adenine on the anti‐syn equilibrium is described and an increased stabilization of the syn conformer, due to selective methylation, is calculated. A moderate anti‐syn activation energy has been found in the case of dm3A, dm6A and dm7A, whereas for dm8A a considerably higher anti‐syn energetic barrier exists. The results are combined with stereo model studies and related to biological data. With respect to restriction‐modification systems, special attention is given to the computed stereochemical freedom of the methyl group in dm6A, with a significant preference for the syn conformation in dm8A being found, leading to the suggestion that, out of the various methylated structures studied, only alternating d(m8A‐T) stretches are able to adopt a Z‐DNA duplex.
The photochemistry of 1‐, 3‐ and 4‐phenyl‐substituted 1,2‐dihydronaphthalenes
Authors: Lamberts J. J. M. , Laarhoven W. H.
Published: September 2010

The photochemical behaviour of 4‐phenyl‐1,2‐dihydronaphthalene (8) is similar to that of unsubstituted 1,2‐dihydronaphthalene (1). The main product is the 1‐phenylbenzobicyclo[3.1.0]hex‐2‐ene (10). 3‐Phenyl‐ and 1‐phenyl‐1,2‐dihydronaphthalenes (14 and 17) behave differently. 14 is photostable and 17 yields only the exo‐isomer of 4‐phenylbenzobicyclo[3.1.0]‐hex‐2‐ene, instead of a mixture of the endo‐ and exo‐isomer as would be expected. The different results are probably due to differences in the steric requirements of the first intermediate formed in the photoconversion.
Linear versus bent transition‐state structures in hydride‐transfer processes mediated by NAD(P)H model systems; a theoretical investigation
Authors: van der Kerk S. M. , van Gerresheim W. , Verhoeven J. W.
Published: September 2010

The reaction‐coordinate for degenerate hydride‐transfer between 1,4‐dihydro‐pyridine and the pyridinium‐ion was searched by MNDO calculations. A linear transition‐state (TS) structure is found to be strongly (> 16 kcal/mole) preferred over a bent TS. In the former, rotation about the C‐hydride‐C axis occurs unimpeded, thus creating a continuum of linear TS‐structures with ring to ring orientations varying between exo and endo.
Gas‐phase thermolysis of tert‐butyl hydroperoxide in a nitrogen atmosphere. The effect of added toluene
Authors: Mulder Peter , Louw Robert
Published: September 2010

Gas‐phase thermolysis of tert‐butyl hydroperoxide 1, ≤1% m in nitrogen (pyrex reactor, atm. pressure, 200‐300°C), gives methane and acetone as the main products. The homolytic mechanism involves O‐O bond dissociation (eqn. 1) and induced decomposition of 1 by hydroxyl and methyl radicals (eqn. 3).

In the presence of a ≥50 fold excess of toluene, reaction (3) is suppressed, •OH and part of the •Me radicals abstracting hydrogen from toluene (eqn. 9).

Values for k3b and k9b (abstraction by •Me) are derived and discussed. Arrhenius parameters for k1, log A/s−1 = 15.3, EA = 41.4 kcal/mol, are in agreement with the thermochemistry and with the results of the VLPP studies of Benson et al.
Stereochemistry of electrophilic addition reactions to 22E‐unsaturated sterols; a Barton rule revisited
Authors: Zeelen F. J.
Published: September 2010

Comparison of the X‐ray structures of seven 22E‐unsaturated sterols shows that these have the same conformation around the double bond. This minimum‐energy conformation has been used by Barton and others to explain the stereoselectivity observed in electrophilic addition reactions. The present study shows that this is only possible when the energy of the transition state of the addition reactions is low.
Pyrolysis of benzene and chlorobenzene in an atmosphere of hydrogen; formation of methane
Authors: Louw Robert , Dijks Johannes H. M. , Mulder Peter
Published: September 2010

Vapours of benzene and derivatives such as chlorobenzene are thermally unstable above ca. 500°C in both nitrogen and hydrogen atmospheres. Major products range from biaryls at lower temperatures to carbon black at temperatures above 1000°C. In hydrogen, dechlorination (ArCl → ArH) is a prominent reaction of (poly)chlorinated benzenes.

In hydrogen, between 500‐1000°C, τ ∼ 5‐10 s, biaryl formation is accompanied by production of comparable amounts of methane. This reaction, for the major part, is shown not to be due to hydrogenolysis of carbonaceous deposits or of the small quantities of ethane/ethene which are also formed.

A mechanistic rationale is presented based on isomerization of cyclohexadienyl radicals (formed in equilibrium with arene and •H), ultimately leading to •CH3 as the precursor of methane.
Synthesis of 6, 14‐ethenoisomorphinans and 6, 14‐ethenomorphinans based on Diels‐Alder adducts of 6‐demethoxythebaine and 6‐demethoxy‐β‐dihydrothebaine; pharmacology of the isomorphinans (Chemistry of Opium Alkaloids, Part XIX)
Authors: Crabbendam P. R. , Lie T. S. , Linders J. T. M. , Maat L.
Published: September 2010

Two different types of Diels‐Alder additions to morphinan‐6, 8‐dienes have been found. 6‐Demethoxythebaine (2) yielded ethyl 4, 5α‐epoxy‐3‐methoxy‐N‐methyl‐6, 14‐ethenoisomorphinan–7α‐carboxylate (3) with ethyl acrylate, in analogy to the reaction with thebaine. The ester 3 was converted into the alcohol 4, of which the 3‐methoxy ether was hydrolyzed to yield 5. Similarly, 2 gave the 7α‐acetyl‐6, 14‐ethenoisomorphinan 7 with methyl vinyl ketone. The latter compound was converted into 4 using methylmagnesium iodide. With propylmagnesium bromide, 7 afforded four compounds; two are new etorphine analogues (8 and 9), to which we were able to assign the absolute configuration; the other two are the Grignard reduction products 10 and 11.

When the 4, 5α‐epoxy bridge of 2 is first opened, the Diels‐Alder reaction with methyl vinyl ketone proceeds from the other side of the diene system yielding the 7β‐acetyl‐6, 14‐ethenomorphinan 6, which belongs to a novel class of rigid morphinans.

Preliminary pharmacological screening of 5, 8 and 9 showed these compounds to be potent agonists.
Enamine synthesis using the Horner‐Wittig reaction. Part 2. New acyl anion equivalents derived from (aminomethyl)diphenylphosphine oxides
Authors: Broekhof N. L. J. M. , van Elburg P. , Hoff D. J. , van der Gen A.
Published: September 2010

Using the Horner‐Wittig reagents (1‐morpholino‐alkyl)diphenylphosphine oxides (1), aromatic as well as aliphatic and α, β‐unsaturated aldehydes can be converted into the morpholino enamines of their respective homologous phenyl, ethyl and styryl ketones. These enamines can be easily converted into the corresponding ketones by mild, acid‐catalyzed hydrolysis. The usefulness of these phosphine oxides as acyl anion equivalents is further demonstrated by the synthesis of dihydrojasmone and of (Z)‐6‐henicosen‐ll‐one.
Facile synthesis of permethyl yttrocene hydride
Authors: den Haan Klaas H. , Teuben Jan H.
Published: September 2010

A convenient three step synthesis of (Cp*2YH)n (Cp* = C5Me5) is described starting with YCl3·3thf, in which Cp*2YCl·thf and Cp*2YCH(SiMe3)2 are intermediates, which could be isolated and characterized. The hydride is active in the activation of sp2 and sp3 C‐H bonds as was demonstrated by the H‐D exchange between C6D6 and the methyl groups of CH2(SiMe3)2 at room temperature.
Oxidative and reductive ring opening of endo‐3,4‐O‐(4‐methoxybenzylidene) acetals of 1, 6‐anhydro‐β‐D‐galactopyranoses
Authors: Kloosterman M. , Slaghek T. , Hermans J. P. G. , van Boom J. H.
Published: September 2010

Cleavage of the endo‐3, 4‐O‐(4‐methoxybenzylidene) acetal rings of 1, 6‐anhydro‐β‐D‐galactopyranose derivatives with LiAlH4‐AlCl3, NaCNBH3‐HCl or NMe3‐AlCl3 gives predominantly axial 3‐O‐(4‐methoxybenzyl) ether derivatives. Oxidative opening of the same acetal functions with DDQ affords the corresponding 3‐O‐(4‐methoxybenzoyl) derivatives. The (4‐methoxybenzyl) group can be removed selectively with DDQ and survives acetolysis of the 1, 6‐anhydro bond.
α‐Imino sulfenates and α‐imino sulfoxides via electrophilic alkylation of amino sulfines (thioamide S‐oxides)
Authors: Lenz Bodo G. , Zwanenburg Binne
Published: September 2010

Treatment of amino sulfines (thioamide S‐oxides) 1 with triethyloxonium tetrafluoroborate, followed by sodium carbonate, leads to α‐imino sulfenates 3. Reaction of 3 with primary and secondary amines gives α‐imino sulfenamides 5. Treatment of amino sulfines with sodium hydride, followed by an alkyl halide, leads to the formation of α‐imino sulfoxides 6, which are extremely sensitive towards hydrolysis. With ketenes, the imines 6 undergo a [2 + 2] cycloaddition reaction to give β‐lactams 8 in low yield.
Glucose‐isomerase‐catalyzed D‐glucose‐D‐fructose interconversion: Mechanism and reactive species
Authors: Makkee M. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

The isomerization of (1‐13C)‐D‐glucose to an equilibrium mixture of (1‐13C)‐D‐glucose and (1‐13C)‐D‐fructose by the enzyme glucose isomerase (E.C. 5.3.1.5) has been followed using 13C NMR spectroscopy. It is concluded that the α‐D‐glucopyranose and the α‐D‐fructofuranose form are the reactive species for the enzyme.
Steric control in the photochemical (E)‐(Z) isomerization of some (over)crowded α‐oxo oxime ethers
Authors: Buys Theo S. V. , Cerfontain Hans , Geenevasen Jan A. J. , Koppes Margareth J. C. M. , Stunnenberg Frank
Published: September 2010

The photoisomerization of a series of (highly) crowded α‐oxo oxime ethers (3–8) has been studied under conditions of direct irradiation (λ 300 and 350 nm) and of triplet photosensitization. The decay ratios k5/k6 for the two conditions are the same for a given compound, illustrating that the isomerization of the α‐oxo oxime ethers, upon direct irradiation, also proceeds from the (lowest) excited triplet state. The excited singlet and triplet state energies are reported, as well as ΔG0(E)‐ΔG0(Z) for 4 (‐ 8.2 ± 0.5) and 6 (7.7 ± 0.5 kJ·mol−1), determined by thermal equilibration with I2 at 353 K. The decay ratio k5/k6 is significantly smaller for 4 and 5 than for 3 and 6‐8 due to steric hindrance upon relaxation of the perpendicular ground state to the (E)‐isomer of 4 and 5.
The photochemical (4 + 2)‐cycloaddition of ortho‐quinones to triarylketenimines
Authors: Baaij J. P. B. , Kamphuis J. , Bos H. J. T.
Published: September 2010

The photochemical reaction of ortho‐quinones with triarylketenimines 4 yields quantitatively the dihydrodioxin derivatives 5 via a (4 + 2)‐cycloaddition. Kinetic studies on the photochemical reaction of phenanthrenequinone (PQ) with N‐(p‐tolyl)dipheriylketenimine show that the reaction proceeds irreversibly, probably via an exciplex of triplet PQ with the CC double bond and an allylic biradical: k2 = (1.18 ± 0.03)·109 1·mol−1·s−1 at 25°C in benzene (Scheme 2). Competition experiments between triplet PQ and N‐phenyl‐substituted triphenylketenimines (Ph2C = C = N − C6H4 − X) gave a good correlation between the relative rate constants and the normal Hammett σ‐constants ρ = −0.31, which indicates the absence of conjugation between the substituent X and the reaction centre at the C  C double bond and confirms the electrophilic character of triplet phenantrenequinone. From the Taft's DSP equation it follows that the blending constant λ = ρI/ρR = 1.02.
Stereospecific reactions of the bicyclo[5.4.1]dodecapentaenyl cation
Authors: Brounts Ronald H. A. M. , Buck Hendrik M.
Published: September 2010

Quenching of the bicyclo[5.4.1]dodecapentaenyl cation 1 with LiOMe/MeOH afforded endo‐4‐methoxy‐syn‐bicyclo[5.4.1]dodeca‐2,5,7,9,11‐pentaene with the methoxy group in a highly crowded position. The remarkable reactivity of cation 1 can be explained by the intermediacy of a syn transition state having a homocyclopropenyl‐type cation at the exo face of the carbon skeleton. Quenching of 1 with the more bulky acetate anion gave the thermodynamically favoured exo‐4‐acetate derivative.
On the synthesis of 1,n‐diketones using mono‐substituted derivatives of tosylmethyl isocyanide
Authors: van Leusen Albert M. , Oosterwijk Roelof , van Echten Erik , van Leusen Daan
Published: September 2010

A new method is described for the synthesis of symmetrical and unsymmetrical diketones. Particularly good results are obtained in the synthesis of 1,6‐ and 1,5‐diketones. Procedures are reported for 1,2‐diketones. The moderate results obtained for 1,4‐diketones and the lack of success for 1,3‐diketones are discussed.
Mild procedures for the synthesis of 1,6‐anhydroaldohexopyranoses
Authors: Kloosterman M. , Dees M. J. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Penta‐O‐acetyl‐β‐D‐galactopyranose was converted in two steps into pentabromophenyl 1,2,3,4‐tetra‐O‐acetyl‐β‐D‐galactopyranoside. Short treatment of the latter with tetra‐n‐butylammonium hydroxide at 20°C, followed by acetylation, afforded crystalline 2,3,4‐tri‐O‐acetyl‐1,6‐anhydro‐β‐D‐galactopyranose. The same procedure could also be applied to the synthesis of the per‐O‐acetates of 1,6‐anhydro‐β‐cellobiose and 1,6‐anhydro‐β‐D‐glucopyranose. 2,3,4‐Tri‐O‐acetyl‐1,6‐anhydro‐β‐D‐glucopyranose could also be obtained in a one‐flask procedure by selective tosylation of D‐glucose at the primary hydroxyl group, followed by treatment with base and subsequent acetylation.
The meta‐photocycloadditions of 3‐ and 4‐cyanoanisole to cyclopentene
Authors: Osselton E. M. , Lempers E. L. M. , Cornelisse J.
Published: September 2010

The results of the meta‐photocycloaddition of cyanoanisoles to cyclopentene are in agreement with a mechanism involving a dipolar species. The adducts undergo thermal and photochemical rearrangements.
Reaction of NADH models with methylene blue
Authors: Engbersen J. F. J. , Koudijs A. , van der Plas H. C.
Published: September 2010

The NADH models, (1R)‐1,4‐dihydronicotinamide and (1R)‐1,4‐dihydroquinoline‐3‐carboxamide (1‐4, R = X‐benzyl or octyl), are readily oxidized by methylene blue (MB⊕), yielding the corresponding pyridinium ions and leuco‐methylene blue (MBH). Under aerobic reaction conditions, molecular oxygen, present in the reaction solution, rapidly reoxidizes MBH to MB⊕, thereby allowing the study of the oxidation of the NADH models under pseudo‐first‐order reaction conditions. In order to elucidate the mechanism of the oxidation of the NADH models by MB⊕, the influence of the MB⊕ concentration, solvent and temperature has been studied as well as the effect of substituent variation in the benzyl group in a series of 1‐(X‐benzyl)‐1,4‐dihydronicotinamides (1a‐f). For one of the model compounds, 1‐benzyl‐1,4‐dihydronicotinamide (1a, BNAH), the primary and the secondary isotope effect and the temperature dependence of the kinetic isotope effect have been determined. It is concluded that oxidation of the NADH models by MB⊕ most likely proceeds by a rate‐determining hydride transfer process via a linear, symmetrical transition‐state structure.
The reactivity of azepinyl anions, derived from 2‐(diethylamino)‐5‐phenyl‐3H‐azepines, towards alkylating agents
Authors: Streef J. W. , van der Plas H. C. , Nieman N. , Stam C. H.
Published: September 2010

Treatment of 2‐(diethylamino)‐3‐(methylthio)‐5‐phenyl‐3H‐azepine (3b, R = SMe) with potassium amide in liquid ammonia, followed by reaction of the anion formed with methyl iodide, gave 2‐(diethylamino)‐5‐methyl‐3‐(methylthio)‐5‐phenyl‐5H‐azepine (5a), the structure of which was confirmed by X‐ray analysis. Substitution at position 5 (as well as at C‐3) was also observed on reacting the anion of 2‐(diethylamino)‐5‐phenyl‐3H‐azepine, obtained by deprotonation of its conjugate acid with lithium diisopropylamide in N,N,N′,N′‐tetramethyl‐1,2‐ethanediamine, with different alkyl halides.
Acid‐catalyzed hydrolysis of benzenesulfonamides. Rate enhancements by ortho‐alkyl substituents
Authors: Wagenaar Anno , Kirby Anthony J. , Engberts Jan B. F. N.
Published: September 2010

Pseudo‐first‐order rate constants have been measured for the acid‐catalyzed hydrolysis of a series of N,N‐dimethyl‐ and N‐methyl‐N‐phenylbenzenesulfonamides in 70% (v/v) CF3CO2H/H2O at 99°C. Analysis of the effect of alkyl substituents in the benzene ring shows a remarkable rate enhancement by ortho‐alkyl groups, in contrast with a rate retardation of similar substituents in the corresponding benzamides. The rate enhancement in the sulfonamides is attributed to relief of initial‐state strain in the transition state for hydrolysis. When the sulfonamide moiety is contained in a five‐membered ring fused to a phenyl ring, the rate of hydrolysis is markedly reduced by an ortho‐methyl substituent.
Diels‐alder reaction of thebaine via N‐formylnorthebaine with nitroethene; reduction of the nitro group in 7α‐nitroethenoisomorphinans (chemistry of opium alkaloids, part XX)
Authors: Maat L. , Peters J. A. , Prazeres M. A.
Published: September 2010

Thebaine (1) was converted into N‐formylnorthebaine (4) via N‐demethylation using diethyl azodicarboxylate followed by treatment with ethyl formate. Diels‐Alder reaction of 4 with nitroethene yielded 5 exclusively with the 6α,14α‐etheno bridge and the nitro group in the 7α‐position. Hydrolysis of 5 and methylation then gave 7, the nitroethene addition product of thebaine. Reduction of 5 and 7 with aluminium amalgam gave the corresponding 7α‐amines 11 and 8, respectively. Reduction of 7 with formamidinesulfinic acid or with lithium aluminium hydride gave only the oxime 9.
The co‐oxidation reaction of isoprene and some aromatic thiols
Authors: van der Laan R. , Moolenaar M. J. , de Koning H. , Huisman H. O.
Published: September 2010

The co‐oxidation reaction between isoprene, some aromatic thiols and molecular oxygen is described. The product distribution, in relation to the nature of the aromatic thiol used, is examined. Steric and electronic factors are discussed.
Isomerization of 4,6‐O‐alkylidene‐1,2‐O‐carbonyl‐α‐D‐galactopyranoses into the corresponding 3,4‐acetals
Authors: Hoogerhout P. , Kloosterman M. , van Boom J. H.
Published: September 2010

1,2‐O‐Carbonyl‐4,6‐O‐ethylidene‐ (4), 4,6‐O‐benzylidene‐1,2‐O‐carbonyl‐ (6) and 1,2‐O‐carbonyl‐4,6‐O‐(p‐methoxybenzylidene)‐α‐D‐galactopyranose (7) were prepared from the corresponding 4,6‐O‐alkylidene‐D‐galactopyranoses (1, 2 and 3) by reaction with 1,1′‐carbonyldiimidazole and the isomerization of 4, 6 and 7 into the 3,4‐acetals 8, 10 and 11 (endo/exo mixtures) by various (Lewis) acids studied.
Vitamin‐C‐ and isovitamin‐C‐derived chemistry. Part I. Synthesis of 2,3‐dideoxy derivatives of the Ascorbic acids
Authors: Vekemans Jozef A. J. M. , Boerekamp Jack , Godefroi Erik F. , Chittenden Gordon J. F.
Published: September 2010

5,6‐O‐Isopropylidene‐L‐gulono‐ and ‐D‐mannono‐1,4‐lactones are converted into 2‐(dimethylamino)‐1,3‐dioxolane derivatives on treatment with N,N‐dimethylformamide dimethyl acetal in chloroform with azeotropic removal of the methanol thus formed. Quaternisation of the products with iodomethane, followed by thermal decomposition yields the corresponding C(4)‐substituted enantiomeric butenolides. Some aspects of the reactions, the characterisation of the products, and further transformations are described.
Solvent‐Reactant‐Support interactions in liquid‐phase hydrogenation II. Supported metal catalysts modified by a liquid film
Authors: Wismeijer A. A. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

The effect of impregnating metal on carbon catalysts with liquid films, immiscible with the bulk solvent, on rate and selectivity in liquid‐phase hydrogenations has been investigated. Both acid and alkaline films have been used with benzene and phenol as the reactant. The bifunctional character of such catalysts has been demonstrated and a substantial improvement in selectivity for the hydrogenation of phenol to cyclohexanone has been achieved. The factors contributing to the observed phenomena in such multiphase catalytic reactions are discussed.
Synthesis of 4‐O‐(3,4,6‐tri‐O‐acetyl‐2‐deoxy‐2‐phthalimido‐β‐D‐glucopyranosyl)‐1,6‐anhydro‐3‐O‐(4‐methoxybenzoyl)‐β‐ D‐mannopyranose: A versatile intermediate for the preparation of N,N‐diacetylchitobiose derivatives
Authors: Kloosterman M. , Westerduin P. , van Boom J. H.
Published: September 2010

4‐O‐Acetyl‐1,6‐anhydro‐3‐O‐(4‐methoxybenzoyl)‐β‐D ‐mannopyranose was converted in two steps into 4‐O‐acetyl‐1,6‐anhydro‐2‐deoxy‐2‐phthalimido‐β‐D‐glucopyranose. Trimethylsilyl tri‐fluoromethanesulphonate‐catalysed coupling of 1,6‐anhydro‐2,3‐O‐(4‐methoxybenzylidene)‐β‐D‐mannopyranose with 1,3,4,6‐tetra‐O‐acetyl‐2‐deoxy‐2‐phthalimido‐β‐D‐glucopyranose, followed by treatment with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone, afforded the title compound. After triflation, the disaccharide thus obtained was treated with lithium azide or potassium phthalimide to afford 4‐O‐(3,4,6‐tri‐O‐acetyl‐2‐deoxy‐2‐phthalimido‐β‐D‐ glucopyranosyl)‐1,6‐anhydro‐2‐azido‐3‐O‐(4‐methoxy‐benzoyl)‐2‐deoxy ‐β‐D‐glucopyranose and 4‐O‐(3,4,6‐tri‐O‐acetyl‐2‐deoxy‐2‐phthalimido‐β‐D ‐glucopyranosyl) −1,6‐anhydro‐2‐deoxy‐3‐O‐(4‐methoxybenzoyl)‐2‐phthalimido‐β‐ D‐glucopyranose, respectively.
Substituent effects on the meta photocycloaddition of arenes to alkenes
Authors: Osselton E. M. , Lempers E. L. M. , Eyken C. P. , Cornelisse J.
Published: September 2010

The meta photocycloaddition of cyano‐ and (trifluoromethyl)‐substituted anisoles to cyclopentene has been investigated and the product ratios are shown to be compatible with a polar mechanism. The photochemical and thermal interconversions of the major adducts from 3‐cyanoanisole and cyclopentene have also been investigated.
Alkaline degradation of monosaccharides III. Influence of reaction parameters upon the final product composition
Authors: de Bruijn J. M. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

A systematic investigation of the alkaline degradation of monosaccharides is presented. The influence of several parameters upon the degradation reaction has been determined by analysis of the reaction products using HPLC and, in some cases, GC. The HO− and the monosaccharide concentrations markedly influence the final product composition with respect to both the amount of C1 to C6 acids and the formation of oligomeric acidic products, the so‐called > C6 acids. Maximum yields of these > C6 acids, up to 50 mol‐C6‐%, are obtained at an HO− concentration of between 10−3 M and 10−2 M when the monosaccharide concentration exceeds 10−2 M. The presence of divalent calcium increases the retro‐aldolization of monosaccharides in alkaline medium, as illustrated by the enhanced production of lactic acid, by complexation with, for instance, d‐fructose. Borate partly protects monosaccharides against alkaline degradation through their borate esters, whilst the amount of saccharinic acids in the degradation product mixture is doubled. On the other hand, neither chloride and carbonate nor the reaction temperature influences the final product composition. Alkaline degradation experiments with pyruvaldehyde, glyceraldehyde and 1,3‐dihydroxyacetone, all assumed to be reaction intermediates, indicate that aldolization of (di)carbonyl compounds causes the formation of substantial amounts of > C6 acids.
1,3‐Halogen shift of 2‐halogeno‐4,5‐dimethylphenols following oxidation with Fremy's salt
Authors: Jacobs A. W. C. M. , Maat L.
Published: September 2010

Oxidation of 2‐bromo‐6‐deuterio‐4,5‐dimethylphenol with Fremy's salt, followed by in situ reduction, yielded mainly 3‐bromo‐4,5‐dimethylpyrocatechol**, which affords evidence for a 1,3‐bromine shift during the oxidation. The same treatment of 2‐chloro‐4,5‐dimethylphenol yielded 4,5‐dimethylpyrocatechol with a minor amount of 3‐chloro‐4,5‐dimethylpyrocatechol. The 2‐iodo compound gave 4,5‐dimethylpyrocatechol as the only reaction product
2,4‐O‐benzylidene‐D‐ribono‐1,5‐lactone: A revision of structure
Authors: Chittenden Gordon J. F. , Regeling Henk
Published: September 2010

The main product resulting from the reaction of d‐ribonolactone with benzaldehyde dimethyl acetal is a 2,3‐O‐benzylidene derivative of the 1,4‐lactone, and not the 2,4‐O‐benzylidene analogue of the 1,5‐lactone, as suggested previously. Chemical and physical evidence supports the re‐assigned structure.
II. Thermal nitration of olefins with tetranitromethane. Evidence for homolytic initiation of a chain mechanism
Authors: Masnovi J. M. , Kochi J. K.
Published: September 2010

Tetranitromethane (TNM) reacts spontaneously with N‐vinylcarbazole to afford the product of 1,2‐addition. Under the same conditions, 9‐vinylanthracene and other olefins do not react with TNM until they are deliberately stimulated by a short pulse of visible light. Photo‐activation under these conditions is associated with the charge‐transfer excitation of the olefin‐TNM complex to produce NO2. The subsequent homolytic addition of NO2 to the olefinic donor, followed by electron transfer of the radical adduct, is responsible for the novel chain mechanism for TNM addition in Scheme 1. Homolytic initiation can also be achieved chemically with various additives such as the electron‐rich ferrocene, N,N,N′,N′‐tetramethyl‐1,4‐phenylenediamine, and 5H‐dibenz[b,f]azepine which generate NO2 by dissociative electron attachment to TNM. The limited quanta of light and traces of chemical initiators indicate that the chain mechanism for the addition of TNM occurs with relatively long kinetic chain lengths. The mechanistic implications of the chain mechanism for the formation of various types of products is discussed in the context of olefin structures.
Ene reactions with α‐chloronitroso compounds: Asymmetric synthesis of N‐allylhydroxylamines
Authors: Kreße G. , Felber H. , Ritter A. , Ascherl B. , Vasella A.
Published: September 2010

The α‐chloronitroso mannose derivative 1 undergoes ene reactions with alkenes 2 to yield nitrone hydrochlorides 3 which may be hydrolyzed to allylic hydroxylamines. The enophilic reactivity of 1 is much higher than that of other α‐chloronitroso compounds. The reaction seems to be highly diastereoselective.
Synthesis and silver‐ion‐catalyzed reactions of 3,3′‐ethylenebicyclopropenyl
Authors: Peelen F. C. , Landheer I. J. , de Wolf W. H. , Bickelhaupt F.
Published: September 2010

The title compound 2 was obtained from 1,2‐dimethylenecyclobutane (1) by double addition of dibromocarbene to give the tetrabromide 9, followed by tin hydride reduction to the dibromide 10 and potassium tert‐butoxide elimination of HBr to furnish 2. Silver‐ion‐catalyzed reaction of 2 did not furnish the expected 1,2‐ or 1,4‐ethylene Dewar benzenes 3 and 4, respectively. Instead, in CDCl3 or dioxane, polymeric material was obtained, while in methanol or methanol‐O‐d1, opening of one or both cyclopropene rings and addition of methanol gave 11 or 12E/Z, respectively, depending upon the reaction conditions. The two latter compounds provide valuable information about intermediate 13 in the silver‐ion‐catalyzed rearrangement of bicyclopropenyls to Dewar benzenes. The mechanism of this reaction is discussed.
A double singlet oxygen oxidation in the formation of α, β‐unsaturated lactones
Authors: Wasserman Harry H. , Lu Ta‐Jung
Published: September 2010

Systems containing both oxazole and selenide units may be constructed so as to yield α,β ‐unsaturated triamides in one step on dye‐sensitized photooxidation. These products may serve as precursors of α,β ‐unsaturated lactones
A highly efficient synthesis of (R)‐ and (S)‐citramalic acid
Authors: Staring Emiel G. J. , Moorlag Henk , Wynberg Hans
Published: September 2010

An efficient multigram synthesis of optically pure (S)‐ and (R)‐citramalic acid is described.
Cyclopropanation of olefins by ethyl diazoacetate: Copper‐ and copper‐complex‐containing X‐zeolites as the catalysts
Authors: Oudejans J. C. , Kock‐Van Dalen A. C. , van Bekkum H. , Kaminska J.
Published: September 2010

Cyclopropanation of olefins by ethyl diazoacetate has been carried out making use of the catalytic action of Cu‐loaded X‐type zeolites upon the decomposition of ethyl diazoacetate. The activity of the NaCuX zeolites is linearly dependent upon the Na‐exchange level. Compared to conventional copper catalysts, the zeolite catalysts give rise to relatively low amounts of polymeric side‐product which is assumed to be formed at the outer zeolite surface. The stereoselectivity obtained with the zeolite catalysts does not deviate significantly from that obtained using copper salts. Zeolite X, loaded with chiral copper complexes, gives rise to only minor asymmetric induction upon cyclopropanation of 1,1‐dichloro‐4‐methyl‐1,3‐pentadiene with ethyl diazoacetate.
Synthesis and properties of peripherally substituted phthalocyaninatocobalt complexes with bisaxially coordinated ligands
Authors: Hanack Michael , Fay Reinhold
Published: September 2010

The synthesis and characterization of peripherally substituted phthalocyaninatocobalt compounds, RmPcCoCl2 and Na[RmPcCo(CN)2] with R = CH3, OCH3, Cl, m = 8; R = t‐Bu, NO2, m = 4, are reported. The latter can be obtained via two methods: either by treatment of RmPcCoCl2 with sodium cyanide or by the reaction of RmPcCo with sodium cyanide in the presence of oxygen. Starting from Na[RmPcCo(CN)2], with R = CH3, m = 8 and R = NO2, m = 4, the corresponding cyano‐bridged polymers, [RmPcCoCN]n, were obtained. The IR, FIR, UV/VIS, 1H NMR (in part) and TG/DTA data are discussed in detail for all the compounds prepared. [(CH3)8PcCoCN]n showed a powder conductivity of σRT 5 · 10−5 S/cm (E 0.22 eV), whereas [(NO2)4PcC(CN)]n has a much lower value, σRT 3 · 10−9 S/cm.
The crystal and molecular structure of aminocyclopropane
Authors: de Boer J. S. A. M. , Schenk H. , Stam C. H.
Published: September 2010

C3H5NH2 has a rhombohedral space group R3c, a = 18.784(2), c = 5.494(2) Å (170.5 K), Z = 18. The final R for 1028 reflexions is 0.035. The molecule has an s‐trans pyramidal conformation and the ring bond lengths, after correction for thermal motion, are; vicinal 1.500(3) and 1.497(3), distal 1.506(3) Å. C‐N 1.457(2) Å.
Alkaline degradation of monosaccharides V: Kinetics of the alkaline isomerization and degradation of monosaccharides
Authors: de Bruijn J. M. , Kieboom A. P. G. , van Bekkum H.
Published: September 2010

A new kinetic model for the alkaline isomerization and degradation of monosaccharides is presented which includes the interconversion of D‐glucose, D‐fructose, D‐mannose and D‐psicose. Computer simulations using this model fit the experimental data and allow the determination of all relevant reaction rate constants. Additionally, it has been established that, for the alkaline degradation of either D‐fructose, D‐glucose or D‐mannose, substantial amounts of acidic products, i.e. ∼65% and ∼20%, are formed via D‐fructose and D‐psicose, respectively.

The influence of some reaction parameters on the pseudo‐first‐order rate constants involved in the kinetic model has been investigated. The enolization of monosaccharides appears to be the rate‐limiting step in both the isomerization and the degradation reactions. The enolization rate is markedly enhanced at higher HO− concentration or by the addition of calcium(II). Direct retro‐aldolization of D‐fructose and D‐psicose occurs at [HO−] > 10−2 M or in the presence of calcium(II), leading to an additional increase in the degradation rate towards lactic acid. The shift of the isomerization equilibrium by borate towards D‐fructose and D‐psicose is accompanied by a decrease of the degradation rate constants, due to stabilization of the monosaccharides as their borate esters.
Spectroscopic characterization of 1‐methylene‐2‐vinylcyclopropane and some of its derivatives
Authors: Brouwer A. M. , Jacobs H. J. C.
Published: September 2010

The characteristic NMR and vibrational spectroscopic properties of 1‐methylene‐2‐vinylcyclopropane 1 and some of its derivatives are described and discussed. The exocyclic CC stretching vibration is consistently found at 1745 cm−1. The 1H NMR spectra show coupling patterns among the methylene and ring protons that are essentially independent of the substituents. The coupling constant between H‐2 and the α‐proton of the substituent depends on the conformation. 13C chemical shifts and coupling constants are readily interpreted using common substituent effect rules. MNDO calculations provide proton‐proton distances and bond orders which are used to interpret proton relaxation rates and proton‐proton coupling constants.
TheDiels‐Alderreaction with 6‐methylene‐7‐octenoic acid, a functionalised butadiene
Authors: Cardinale G. , Laan J. A. M. , Ward J. P.
Published: September 2010

A novel functionalised butadiene, 6‐methylene‐7‐octenoic acid, was synthesized from myrcene (7‐methyl‐3‐methylene‐1,6‐octadiene).Diels‐Alderadducts were formed with maleic anhydride and cyclopentene‐3,5‐dione.
A general procedure to convert H‐phosphonate mono‐ or diesters of nucleic acids into valuable phosphate di‐ or triesters
Authors: de Vroom E. , Spierenburg M. L. , Dreef C. E. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Treatment of properly‐protected d‐nucleoside 3′‐H‐phosphonate mono‐ or diesters with N,O‐bis(trimethylsilyl)acetamide, followed by the addition of an appropriate chloride, affords 3′‐phosphate di‐ or triester derivatives, respectively.
(2‐Cyano‐1,1‐dimethylethoxy)bis(diethylamino)phosphine: A convenient reagent for the synthesis of DNA fragments
Authors: Marugg J. E. , Burik A. , van der Marel G. A. , van Boom J. H. , Nielsen J. , Dahl O.
Published: September 2010

The phosphitylating reagent (2‐cyano‐1,1‐dimethylethoxy)bis(diethylamino)phosphine proved to be very effective for the in situ preparation of d‐nucleoside phosphoramidites. These latter compounds could be used for the introduction of 3′,5′‐internucleotide bonds and for the synthesis of DNA fragments both in solution and on a solid support. Removal of the 2‐cyano‐1,1‐dimethylethyl protective group at P(V) could easily be effected by ammonolysis.
A novel synthesis of α‐(phenylthio)aldehydes
Authors: Jansen B. J. M. , Peperzak R. M. , de Groot Ae.
Published: September 2010

Addition of methoxy(phenylthio)methyllithium to ketones, followed by rearrangement of the adducts, provides a new method for the preparation of α‐(phenylthio)aldehydes. The rearrangement is stereospecific.
Selective formation of 1,3,4‐trisubstituted and 3,4‐disubstituted trans‐β‐lactams from zinc enolates and imines
Authors: Jastrzebski Johann T. B. H. , van der Steen Fred H. , van Koten Gerard
Published: September 2010

A new route for the high yield synthesis (better then 90%) of exclusively trans‐β‐lactams (azetidin‐2‐ones) is reported which involves the 1:1 reaction of an α‐aminoacid ester zinc enolate with an appropriate imine. The reaction can be carried out as a ‘one‐pot’ synthesis as has been demonstrated for the synthesis of trans‐3‐diethylamino‐4‐phenyl azetidin‐2‐one (93% yield). The novel zinc enolates have most likely a Z‐geometry as a result of intramolecular chelate coordination. Evidence has been obtained that in the first step these zinc enolates react with the imine in a highly diastereoselective manner providing the threo aldolate which in a subsequent step undergoes ring closure to the azetidin‐2‐one.
The crystal and molecular structure of 3,4‐dihydro‐benzo(a)‐4‐ortho‐hydroxyphenyl‐3,4a‐diazo‐carbazole dimethylamino‐methanal, C20H15N3O. C3H7N O
Authors: Garcia‐Blanco S. , Beurskens Gezina , Beurskens Paul T.
Published: September 2010

The structure of the title compound, C20H15N3O. C3H7N O was determined by X‐ray analysis at T= 298 K, Mr=386.452, monoclinic, space group Cc, a=14.747(1), b=9.860(1), c=13.973(1) Å, β=91.21(1)°, V=2031.3(3) Å3, Z=4, F000=816, Dc=1.264 Mg/m3, CuKα radiation (graphite crystal monochromator, λ=1.5418 A), μ(CuKα)=6.301 cm‐1. The structure was solved by orientation and translation search on a known fragment and expanded with DIRDIF. Final conventional R‐factor=0.092, Rw=0.108 for 1522 unique reflections and 284 variables.
A new approach to annelated furans. The total synthesis of (±)‐euryfuran
Authors: Jansen B. J. M. , Peperzak R. M. , de Groot Ae.
Published: September 2010

A new approach to annelated furans has been developed starting from ketones. Formylation of the enolate, protection of the aldehyde function as its (phenylthio)‐ or (n‐butylthio)methylene derivative and addition of methoxy(phenylthio)methyllithium gave adducts with the necessary functionalized carbon atoms. Rearrangement of these adducts to phenylthio aldehydes, followed by reduction, led to alcohols which spontaneously cyclized to furans. The method has been demonstrated in the total synthesis of (±)‐euryfuran. An unusual rearrangement was found upon hydrolysis of the adducts mentioned above in that a ring expansion leading to γ‐oxo α,β‐unsaturated aldehydes was observed.
Attempted synthesis of a [5](2,5)pyridinophan‐6‐one from its Dewar isomer
Authors: Kostermans G. B. M. , de Wolf W. H. , Bickelhaupt F. , Krever M.
Published: September 2010

The 1,4‐pentamethylene Dewar pyridone 1a was synthesized from 2,9‐undecadiyne (3), aluminium trichloride and phenyl isocyanate. The exclusive formation of 1a at the expense of other possible isomers is discussed and tentatively explained by the regiospecific reactivity of the intermediate 4a. Attempts to convert 1a into the [5] (2,5)pyridinophan‐6‐one 2 by irradiation, thermolysis or acid catalysis did not give the desired result. However, on thermolysis and acid catalysis, 1a rearranges to the ortho‐annelated pyridone 13 in high yield, the structure of which was established by X‐ray‐crystal structure determination. The mechanism of these reactions is discussed.
Synthesis of ribonucleoside 3′,5′‐cyclic phosphorothioates using a modified hydroxybenzotriazole phosphotriester approach
Authors: de Vroom E. , van der Marel G. A. , van Boom J. H.
Published: September 2010

Phosphorothioylation of 3′,5′‐dihydroxyl ribonucleosides with O‐(2‐chlorophenyl) O, O‐bis[6‐(trifluoromethyl)‐1‐benzotriazolyl] phosphorothioate, followed by addition of N‐methyl‐imidazole and removal of protecting groups, gives ribonucleosides 3′,5′‐cyclic phosphorothioates. The latter compounds could also be prepared by phosphorothioylation of 2′,3′,5′‐trihydroxyl ribonucleosides.
Physico‐chemical studies on calcium soaps
Authors: Mehrotra K. N. , Upadhyaya S. K.
Published: September 2010

Calcium soaps were prepared by the metathesis of the corresponding potassium soap with an aqueous solution of calcium acetate. The IR results showed that the fatty acids exist in a dimeric structure as a result of hydrogen bonding between the carboxyl groups of two acid molecules, whereas calcium palmitate has an ionic character. The X‐ray analysis indicated that the zig‐zag chains of the fatty acid radical constituent of the soap molecules extend straightforward on both sides of each basal plane and that the molecular axes of the soaps are slightly inclined to the basal plane. The thermal decomposition of calcium palmitate was found to be kinetically of zero order and the energy of activation for the decomposition reaction was in the region of 3 KJ/mole.
A new model for coenzyme B12
Authors: van Arkel B. , van der Baan J. L. , Balt S. , de Bolster M. W. G. , van Delft R. J. , Klumpp G. W. , de Koning H. , van den Winkel Y.
Published: September 2010

A new cobaloxime‐type model for coenzyme B12 has been synthesized. For this model strong steric repulsion between its dioxymethylene bridge and (one of) the axial ligands on cobalt presages enhanced rates of axial ligand exchange.