bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of neopine and its 5β‐ and 7‐substituted derivatives (chemistry of opium alkaloids, part XL≠)
Authors: Meuzelaar G. J. , Woudenberg R. H. , Sinnema A. , Maat L. 
Published: September 2010

AbstractHeating 14β‐bromocodeine (3) with methanol and triethylamine yielded 6α, 7α‐epoxy‐6‐deoxyneopine (5). The epoxide 5 was reduced to neopine (7) with lithium aluminium hydride, whereas reaction of 5 with sodium methoxide gave 7β‐methoxyneopine (9). Similar reactions were performed with 14β‐bromo‐5β‐methylcodeine (4), yielding the corresponding 5β‐methyl derivatives 6, 8 and 10. Acetylation of 3 and 4 gave 6α‐O‐acetyl‐14β‐bromocodeine (11) and its 5β‐methyl analogue 12, respectively, from which the ortho esters 13 and 14 were obtained after treatment with methanol. Acid hydrolysis of 13 or, better, solvolysis of 11 in water yielded a mixture of 6α‐O‐acetyl‐7α‐hydroxyneopine (15) and 7α‐acetoxyneopine (17). Under the same conditions 12 and 14 gave the 5β‐methyl analogues 16 and 18.
Regioselective introduction of functional groups in α‐diimines by means of dialkylzinc compounds. Synthesis of functionalized 2‐ and 3‐pyrrolidinone derivatives
Authors: Wissing Elmo , Kleijn Henk , Boersma Jaap , van Koten Gerard 
Published: September 2010

AbstractAlkylation of the 1,4‐diaza‐1,3‐butadiene t‐BuN=CH‐CH=N t‐Bu (t‐BuDAB) by functionally substituted diorganozinc compounds Zn[(CHR1XCH2)nXR2]2 (n = 1–3, R1 = H, Me, XR2 = OMe, OBn, SEt, NMe2, COOEt) occurs regioselectively. Alkylation occurs at the nitrogen atom of the N=C‐C=N skeleton of t‐BuDAB when primary diorganozinc compounds are used (R1 = H), but at the carbon atom when secondary and benzylic diorganozinc compounds are employed. The functional groups in the diorganozinc reagents proved to be important for the alkylation reaction only in the case of Zn[(CH2)3NMe2]2 (7) and Zn(C6H4CH2NMe2−2)2 (16), in which the strongly coordinating NMe2 groups give either a decrease of the alkylation rate (7), or no reactivity at all (16). When t‐BuDAB is reacted with Zn[(CH2)2COOEt]2 (10) alone, a 3‐pyrrolidinone (10c) is formed, whereas the same reaction with a mixture of 10 and ClZn(CH2)2COOEt affords a 2‐pyrrolidinone (10b). The reactions involve a two‐step process involving prior regioselective introduction of the alkyl group either at the N or C atom of an imine unit followed by an intramolecular nucleophilic substitution leading to 10b or 10c, respectively. The molecular structure of 10c shows the functionalized heterocycle to be part of a conjugated enamine system.
Synthesis of carba‐strigol analogues
Authors: Kishimba M. A. , Zwanenburg B. 
Published: September 2010

AbstractCarba analogues 1, 14, 15 and 16 of Strigol were synthesised in which the vinyl ether oxygen is replaced by methylene. Compound 1 was prepared by the Wittig reaction of ylid 2 with aldehyde 3. Compounds 14, 15 and 16, for which this approach failed, were prepared by reaction of aldehyde 20 with lactones 17, 18 and 19, respectively, using the method of Tanaka et al.35,36, or with phosphonates 32 and 33, in a Wittig‐Horner reaction. Subsequent oxidative elimination of the thioether moiety gave the desired products.
Peptides from chiral Cα,α‐disubstituted glycines. Synthesis and conformational analysis of homochiral (αMe) Leu / Ala model peptides
Authors: Kamphuis J. , Boesten W. H. J. , Schoemaker H. E. , Aubry A. , Bayeul D. , Dautant A. , Pantano M. , Formaggio F. , Crisma M. , Bonora G. M. , Toniolo C. 
Published: September 2010

AbstractHomochiral (αMe)Leu/Ala and Leu/Ala model peptides were synthesized by solution methods and fully characterized. A solution conformational analysis of the tripeptides was carried out using FT‐IR absorption and 1H NMR. The crystal‐state structure of Z‐D‐(αMe)Leu‐(D‐Ala)2‐OMe monohydrate was resolved by X‐ray diffraction. The results obtained support the conclusion that the tendency of the non‐coded (αMe)Leu residue to fold into β‐bends and helical structures is markedly higher than that of its unmethylated protein counterpart (Leu).
An expeditious route to methylphosphonate analogues of DNA
Authors: Kuyl‐Yeheskiely E. , Meeuwenoord N. J. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractProtection of the exocyclic amino groups of both nucleobases adenine and guanine with the N,N‐dimethylformamidine and cytosine with the isobutyryl group presents a convenient and economical N‐protective‐group‐strategy for the solid‐phase synthesis of DNA fragments containing methylphosphonate linkages at predetermined locations. Thus, the post‐synthesis removal of the N‐protective groups with hydrazine hydrate (16 h at 20°C) afforded immobilized fragments, which were then cleaved from the solid support and deprotected at the phosphorus by treatment with ammonia in methanol (2 h at 20°C) to yield high‐quality products.
Synthesis of six novel retinals and their interaction with bacterioopsin
Authors: Groesbeek M. , Kirillova Y. G. , Boeff R. , Lugtenburg J. 
Published: September 2010

AbstractThe synthesis and spectroscopic characterization of six novel chemically modified retinals, is described, prepared by a single strategy: all‐E‐10,12‐ethanoretinal (1), all‐E‐10,12‐propanoretinal (2), all‐E‐10,12‐ethano‐20‐norretinal (3), all‐E‐20‐nor‐10,12‐propanoretinal (4), all‐E‐12,14‐ethano‐20‐norretinal (5), and all‐E‐20‐nor‐12,14‐propanoretinal (6). For this strategy we developed two novel synthons, 2‐(diethoxyphosphinyl) hexanedinitrile and 2‐(diethoxyphosphinyl) heptanedinitrile which were prepared in their deprotonated form from hexanedinitrile and heptanedinitrile. Bacterioopsin was incubated with each of 1 to 6. Only 1 and 3 form bacteriorhodopsin analogues (bR‐1 and bR‐3). bR‐1 shows light‐dark adaptation and an approx. 50% light‐driven proton‐pump action. bR‐3 does not show light‐dark adaptation or proton‐pump action. It is also shown that the protein can efficiently accommodate retinal with the 10,12‐ethano group whereas the corresponding retinal with the 10,12‐propano group does not fit in the binding site.
Solution structures of hydrido‐rhodium diphosphite hydroformylation catalysts
Authors: van Leeuwen Piet W. N. M. , Buisman Godfried J. H. , van Rooy Annemiek , Kamer Paul C. J. 
Published: September 2010

AbstractThe NMR spectroscopy data for five hydroformylation catalysts RhH(CO)2(P‐P) (P‐P = diphosphite bidentate ligand) are reported and interpreted in terms of equatorial and axial coordination of the phosphorus and carbon monoxide ligands in a trigonal bipyramidal structure.
Conformational analysis of all‐E‐retinal, all‐E‐8,16‐methanoretinal, (1S)‐all‐E‐8,16‐methano‐18‐norretinal, and all‐E‐17,18‐dinor‐8,16‐methanoretinal by means of NMR spectroscopy and molecular dynamics
Authors: Ippel J.H. , Spijker‐Assink M.B. , Groesbeek M. , van der Steen R. , Altona C. , Lugtenburg J. 
Published: September 2010

AbstractThe conformations of all‐E‐retinal (1), (1S)‐all‐E‐8,16‐methano‐18‐norretinal [(1S)‐2], all‐E‐8,16‐methanoretinal (3) and all‐E‐17,18‐dinor‐8,16‐methanoretinal (4) in solution were studied by 1H‐NMR spectroscopy and molecular‐mechanics and molecular‐dynamics simulations. The 1H‐NMR spectrum of 1 is characterized by fast inversion of two half‐chair rings and by a skewed 6‐s‐cis geometry of the polyene chain. Molecular‐dynamics simulations at 1000K on 1 show the existence of two, dynamically stable, skewed 6‐s‐cis conformers (torsion angle C5‐C6‐C7‐C8: 84° and —83°), separated by a 6‐s‐trans transition state. The conformationally locked structures of 2, 3 and 4 have similar conformations and are, in a geometrical sense, ideal model compounds to study rhodopsins with a well‐defined 6‐s‐trans orientation of the chromophore.
Acid‐induced decomposition of coenzyme B12 and variants
Authors: Gerards L.E.H. , Balt S. 
Published: September 2010

AbstractThe acid‐catalyzed heterolytic cleavage of the Co‐C bond in coenzyme B12 (1) and adocobinamide hydroxide (2) was studied using the excess‐acidity functions of Cox and Yates. The results are compared to the acid‐induced decomposition of methyl(5′‐deoxyribofuranosyl)cobalamin (3) and (2‐ethoxyethyl)cobalamin (4). Evidence is presented to view the bond cleavage in the compounds 1, 2 and 3 as an A2 mechanism or as an Ia substitution at Co3+, with water as the nucleophile, and in 4 as an A1 mechanism. For 1, the temperature dependence (289‐320 K) gives ΔS‡ = − 96 J/(K· mol), in agreement with the Ia (A2) mechanism. For the A2 reactions the volumes of activation [ΔV‡ = −11.4 (1), −8.2 (2) and −11.5 (3) cm3/mol in 2‐4M acid at 298K] are consistent with the proposed mechanism, but ΔV‡ for the A1 mechanism of 4 is exceptionally negative (‐7.2 cm3 /mol), probably due to intramolecular coordination in the transition state. A comparison with the much slower acid‐induced decomposition of 5′‐deoxyadenosine brings out the labilization of the furanosyl oxygen bridge by coordination of the 5′‐deoxyadenosyl or 5′‐deoxyribofuranosyl group at the β‐position to cobalt. For 5′‐deoxyadenosine the excess‐acidity treatment and the activation volume (ΔV‡ = 1.7 cm3/mol in 2 M acid) indicate a clear A1 mechanism.
Synthesis of bicyclic 3‐pyrazolidinones via π‐cyclization reactions of exocyclic N‐acylhydrazonium ions
Authors: Rutjes Floris P. J. T. , Udding Jan H. , Hiemstra Henk , Speckamp W. Nico 
Published: September 2010

AbstractThe preparation of several a‐fused 3‐pyrazolidinones is described starting from 5,5‐di‐methyl‐3‐pyrazolidinone and using an acid‐induced cyclization of a π‐nucleophile tethered to N‐1 onto a cationic carbon bonded to N‐2 (an exocyclic N‐acylhydrazonium intermediate). The cyclization reactions proceed best with activated π‐nucleophiles such as allyl‐ and propargylsilanes. In the case of an ester substituent at the cationic carbon, structural analogues of antibacterial bicyclic pyrazolidinones are obtained. The stereochemistry of one product is established by X‐ray crystallographic analysis. Two cyclization products showed NMR spectra with very broad signals due to relatively high nitrogen‐inversion barriers (ca. 13 kcal/mole).
Synthesis and spectroscopic characterisation of 13C‐labelled ubiquinone‐0 and ubiquinone‐10
Authors: van Liemt W.B.S. , Steggerda W.F. , Esmeijer R. , Lugtenburg J. 
Published: September 2010

Abstract(1‐13C)‐, (2‐13C)‐, (3‐13C)‐, (3‐13CH3)‐, (4‐13C), and (13CH3O)2‐ ubiquinone‐10 and the corresponding (1‐13C)‐, (6‐13C)‐, (5‐13C)‐, (5‐13CH3)‐, (4‐13C)‐, and (13CH3O)2‐ubiquinone‐0 have been synthesised from simple labelled starting materials via a single reaction scheme. The ubiquinones have been characterised using mass spectrometry, 1H NMR and 13C NMR. The spectroscopic results indicate that, within experimental error, the syntheses have been accomplished without scrambling or dilution of label. All labelled ubiquinones have been synthesised on a decigram scale.
Aggregation behaviour of a phospholipid based on D‐(‐)‐threitol
Authors: Feiters M.C. , Nolte R.J.M. , Zwanenburg B. 
Published: September 2010

AbstractThe aggregation behaviour of a synthetic C4 phospholipid, containing two phosphate groups and two stearoyl groups, has been studied. The surfactant formed different types of aggregates in water depending on the concentration, the temperature and the treatment of the samples. Tilted bilayers were found at high surfactant concentrations, whereas at low surfactant concentrations intercalated bilayers could be identified. The intercalated structures could be converted into very small vesicles upon sonication. Tube‐like aggregates were formed after storage at low temperature, which coagulated into thread‐like superstructures.
The effects of salts and surfactants on the physical stability of lamellar liquid‐crystalline systems
Authors: van de Pas J.C. , Buytenhek C.J. , Brouwn L.F. 
Published: September 2010

AbstractThe effects of the salting‐out effectiveness of electrolytes and of the salting‐out resistance of surfactants on the physical stability of lamellar phase systems, consisting of sodium dodecylbenzenesulphonate, a co‐surfactant, an electrolyte and water, have been investigated. A correlation was found between (i) the electrolyte concentration necessary to induce salting‐out/phase separation of a micellar solution of the co‐surfactant and (ii) the maximum electrolyte concentration which can be incorporated into a lamellar phase system formed from the co‐surfactant before physical instability is observed. High concentrations of salting‐out electrolyte can be added to lamellar phase systems before instability is observed, when the co‐surfactant has a high resistance against salting‐out effects.
Synthesis and polymorphism of deuterium labeled unsaturated monogalactosyl diglyceride as studied by 2H NMR
Authors: Chupin Vladimir , Smirnova Svetlana , de Kruijff Ben 
Published: September 2010

AbstractThe synthesis and polymorphism of deuterium‐labeled 1,2‐di‐O‐[11‐2H2)‐oleoyl]‐3‐O‐β‐D‐galactopyranosyl)‐rac‐glycerol is described. 2H‐NMR studies show that this lipid in its hydrated state adopts a lamellar phase below ‐ 5°C and an inverted hexagonal phase above ‐ 5°C.
Methacrylate resin membranes by Gel‐Template‐Leaching: Concept and scope
Authors: Gankema Harold , Hempenius Mark A. , Möller Martin 
Published: September 2010

AbstractA method of preparation of microporous membranes is described, based on the removal of a crystalline (perfluoroalkyl)alkane [F(CF2)m‐(CH2)nH] network from a cross‐linked methacrylate matrix. (Perfluoroalkyl)alkanes with a particular (CF2)m/(CH2)n balance form gels of interconnected long‐needle crystals upon crystallization from dilute solution. A template of this gel structure was prepared employing a mixture of suitable methacrylate monomers as a solvent. The solvent was first cured by low‐temperature UV‐initiated copolymerization/cross‐linking and subsequently the crystalline network was removed by extraction or sublimation. The resulting microporous morphologies were monitored by optical microscopy, scanning electron microscopy and scanning force microscopy. The cylindrical pore sizes could be varied deliberately by changing the (perfluoroalkyl)alkane, its concentration, and the degree of undercooling upon gelation. Maximum pore diameters varied between 12 nm and 145 nm. Flux measurements showed a decrease in pore size upon increasing the operation temperature of the membrane. A change in the temperature coefficient has been correlated with the glass transition temperature of the membrane. After saponification of the pore surfaces, the pores became smaller, which is probably due to swelling of the top layer of the surfaces. Introduction of sodium‐sulfonate groups on the inner pore surfaces resulted in a certain cation selectivity.
Second‐harmonic generation from thin films of mixtures of an aggregated chiral 4‐nitroazobenzene dye and amylose acetate
Authors: Schoondorp Monique A. , Schouten Arend Jan , Hulshof Jos B. E. , Schudde Ebe P. , Feringa Ben L. 
Published: September 2010

AbstractSecond‐harmonic generation (SHG) from both Langmuir‐Blodgett (LB) films and solvent‐cast films of mixtures of a chiral nonlinear optical (NLO) dye, an ester of palmitic acid and 4‐nitro‐4′‐[(3R)‐hydroxypyrrolidinyl]azobenzene (KMES16) and amylose acetate is investigated. Results are discussed concerning the structure of the films. The NLO‐active molecules form crystalline domains in which the molecules are aligned anti‐parallel without a centre of symmetry (crystal point group P21). The dye domains behave like H aggregates. LB multilayer films show no significant SHG when measured “as deposited”. After heating and cooling down unexpectedly large SHG is measured. Cast films of the same mixtures also show SHG. The effect is attributed partly to a crystal‐size effect and an enhancement of the SHG by H aggregates is suggested. In this paper, we describe SHG of thin layers without the execution of extended procedures to orient the molecules.
The relationship between the molecular structure of polyhydroxy amphiphiles and their aggregation behaviour in water. I. The contact preparation method as a tool for empirical studies
Authors: van Doren Henk A. , Wingert Lavinia M. 
Published: September 2010

AbstractThe lyotropic liquid‐crystalline behaviour of several dozens of (nonionic) polyhydroxy amphiphiles was studied by observing the penetration of water into the bulk of a sample of amphiphile on a microscope slide and identifying the mesophases observed at the interface with the aqueous solution. The compounds were plotted as a function of the total number of hydroxyl and carbonyl groups vs. the total number of carbon atoms in the (hydrophobic) alkyl chain(s). The symbol used for each compound was chosen to indicate the mesophase observed. In this manner, a clear picture emerged of the relationship between overall molecular structure and type of lyotropic phase(s) formed. Based on this plot it becomes possible to predict the type of lyotropic phase that will be formed at the amphiphile‐water interface. Lyotropic mesophases are generally considered to be built up from the aggregates found in dilute aqueous solution. Therefore, a contact preparation also constitutes a simple test for the prediction of the type of aggregate an amphiphile will form in dilute aqueous solution. A useful tool for the design of new surfactants is thus provided.
Synthesis of 4‐imidazolin‐2‐ones from α‐bromo ketimines
Authors: De Kimpe Norbert , De Smaele Dirk , Stanoeva Elena , Tinant Bernard , Declercq Jean‐Paul 
Published: September 2010

AbstractA novel synthesis of 1,4‐dialkyl‐5‐aryl‐4‐imidazolin‐2‐ones 3 has been achieved by reaction of α‐bromo ketimines 2 with potassium cyanate in dimethylformamide. The structural assignment of these heterocycles was performed by spectrometric methods, comparison with a known compound and X‐ray crystallographic analysis of the acetyl derivative 8.
Synthesis of 5‐(β‐D‐glucopyranosyloxymethyl)‐2′‐deoxyuridine and derivatives thereof. A modified d‐nucleoside from the DNA of Trypanosoma brucei
Authors: Wijsman E. R. , van den Berg O. , Kuyl‐Yeheskiely E. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractAn appropriately protected 3′‐phosphoramidite and 5′‐phosphate derivative of the modified 2′‐deoxyuridine were obtained by β‐glycosylation of a properly protected 5‐hydroxymethyl‐2′‐deoxyuridine, and subsequent elaboration of the resulting intermediates using standard protocols devised in nucleic acids chemistry.
Conformations and rotational barriers of di‐ and tetraarylporphyrins; a computational and experimental study
Authors: Schrijvers Robert , van Dijk Marinus , Sanders Georgine M. , Sudhölter Ernst J. R. 
Published: September 2010

AbstractThe usefulness of molecular‐mechanics calculations in the study of the conformational properties of several tetraarylporphyrins and diarylporphyrins is demonstrated. Energy‐minimized conformations and rotational barriers of several substituted and unsubstituted arylporphyrins correspond very well with experimental results.
Vanadium in cationic and anionic positions as a promoter of 12‐molybdophosphoric‐acid‐based catalysts
Authors: Bergier T. , Brückman K. , Haber J. 
Published: September 2010

AbstractDerivatives of 12‐molybdophosphoric acid (H3PMo12O40), containing vanadium in the form of a vanadyl cation or substituted as addenda in Keggin anions, have been synthesized and characterized by IR, LRS, XPS, NMR, and DTA/DTG. Their catalytic behavior in the oxidation of methanol, butane and pentane has been determined. Both catalysts exhibit strong acidity, due to hydrolysis of the secondary structure in the case of the salt. The vanadium atom performs its role as the active site for the activation of hydrocarbon molecules irrespective of whether it is present as a cation or incorporated in Keggin anions.
On the positional reactivity order in the sulfonation of phenyl‐and naphthyl‐substituted naphthalenes with SO3
Authors: Cerfontain Hans , Zou Yousi , Bakker Bert H. 
Published: September 2010

AbstractThe sulfonation of 1‐ and 2‐phenylnaphthalene, 1,1′‐ and 2,2′‐binaphthyl, and that of the 2,2′‐dihydroxy, 2,2′‐dimethoxy and 2,2′‐dimesyloxy derivatives of 1,1′‐binaphthyl with SO3 in dichloromethane as solvent was studied at 22 ± 2°C. Sulfonation of 1‐phenylnaphthalene and 1,1′‐binaphthyl leads to substitution at (each of) the α‐naphthyl moieties, initially at the 4‐position and subsequently at the 6‐ and 7‐position, in a ratio of approximately 8:92 and 14:86, respectively. Upon sulfonation the more planar 2‐phenylnaphthalene and 2,2′‐binaphthyl both give initially the 8‐sulfonic acid derivative (8‐S) and subsequently a mixture of 8,4′‐S2 and 8,8′‐S2, respectively; their further sulfonation affords mixtures of the 4,8,4′‐S3 + 6,8,4′‐S3 and of the 4,8,8′‐S3 + 6,8,8′‐S3, respectively, both in an isomer ratio of approximately 19:81.Sulfonation of 2,2′‐dimethoxy‐1,1′‐binaphthyl gives initially the 3‐S and 6‐S derivatives in an isomer ratio of approximately 13:87 subsequently the 3,6′‐S2 and 6,6′‐S2 derivatives and eventually the 3,6,4′,6′‐S4 and 4,6,4′,6′‐S4 derivatives. Monosulfonation of 2,2′‐dimesyloxy‐1,1′‐binaphthyl gives the 5‐S and 6‐S in a ratio of 58:42. With a large excess of SO3, 4,6,4′,6′‐S4, 4,6,5′,7′‐S4 and 5,7,5′,7′‐S4 are eventually formed. Sulfonation of 2,2′‐dihydroxy‐1,1′‐binaphthyl gives initially the 5‐S and 6‐S, the ratio of which increases upon increasing the amount of SO3 employed from approximately 35:65 on using ≤ 1.0 mol‐equiv. of SO3 to approximately 62:38 on using > 6.0 mol‐equiv. of SO3. Under the latter conditions the substrate species undergoing sulfonation is proposed to be the di‐sulfated species 3.
Odd‐even effects in the optical properties of chiral twin liquid‐crystalline cholesteryl ω‐(cyanobiphenylyloxy) alkanoates
Authors: Marcelis Antonius T. M. , Koudijs Arie , Sudhölter Ernst J. R. 
Published: September 2010

AbstractA series of novel cholesteryl w‐(cyanobiphenylyloxy)alkanoate esters with a varying number (2–7 and 10) of methylene units in the alkanoate spacer was synthesized and their mesogenic properties were investigated by polarization microscopy and differential scanning calorimetry. All compounds show a broad range of enantiotropic liquid‐crystalline behavior. Both the cholesteric‐isotropic and the smectic‐cholesteric transition temperatures show a pronounced odd‐even effect as a function of spacer length. The selective reflection wavelength of the cholesteric phases has been determined as a function of spacer length and temperature. For the first time, we have shown that the reflection wavelength also shows a pronounced odd‐even effect. The compounds with an even number of methylene units reflect at much lower wavelengths than the compounds with an odd number of methylene units. The reflection wavelength of the latter compounds decreases strongly with temperature, whereas the reflection wavelength of the compounds with the even spacers is almost independent of the temperature. The odd‐even effect in the optical properties attenuates with increasing spacer length.
Synthesis of thiophene‐2‐phosphonates via α,β‐unsaturated sulfines as intermediates
Authors: van der Linden Johannes B. , Lucassen André C. B. , Zwanenburg Binne 
Published: September 2010

AbstractHeteroconjugate addition of various alkyllithium reagents to α‐silylallenephosphonates 3b,c has been accomplished in high yields. The formation of thiophene‐2‐phosphonates 5, by heteroconjugate addition of organolithium to 3bc, followed by treatment with sulfur dioxide, proceeds in reasonable yields via the intermediate formation of α,β‐unsaturated sulfines 4. An alternative synthesis of the heteroconjugate addition product diethyl 1‐(trimethylsily)‐2,3‐dimethylbut‐2‐ene‐1‐phosphonate 6a from 2,3‐dimethylbut‐2‐enyl bromide has also been described.