bluuebunny/crossref_metadata_2025_split huggingface dataset:
Configuration‐dependent conformational transmission in trigonal‐bipyramidal Pv compounds. Enhanced gauche (‐) population around the C(5)‐C(6) linkage in 6‐Pv phosphorylated tetramethyl‐α‐D‐galactopyranoside
Authors: de Vries N. K. , Buck H. M. 
Published: September 2010

AbstractA 300‐MHz 1H NMR variable‐temperature study of the 1′‐phosphorylated trigonal‐bipyramidal (TBP) tetrahydropyran‐2‐methyl model compound 4 is reported. For this compound, in which both the equatorial and axial sites undergoing phosphorus pseudorotation bear a tetrahydro‐pyran‐2‐methyl group, a precise conformational analysis of the C(1′)‐C(2) bond is possible. The thermodynamic parameters which result from this analysis allow the assignment of the proton resonating at low field as H(1′). It is shown that, for the group situated axially in the Pv TBP, an enhanced gauche (‐) population [O(1′) and O(1) trans‐situated] occurs around C(1′)‐C(2) (290 K, 59%; 230 K, 74%) as compared to the corresponding Piv compound 3 (298 K, 10%). The same conformational transmission is observed for 6‐phosphorylated pyranosides, but in this case is found to depend upon the configuration at C(4). It appears that 6‐phosphorylated methyl 2,3,4‐tri‐O‐methyl‐α‐D‐galactopyranoside shows a conformational change around C(5)‐C(6) towards a higher g− population, going from 6‐Piv to 6‐Pv TBP, which is absent in the corresponding 6‐phosphorylated methyl 2,3,4‐tri‐O‐methyl‐α‐D‐glucopyranoside. Apparently, the configuration at C(4) is jointly liable for the transmission in the Pv TBP.
Photochemistry of α‐oxo oximes. Part 9. The γ‐hydrogen abstraction in α‐oxo oxime ethers
Authors: Buys Theo S. V. , Cerfontain Hans , Geenevasen Jan A. J. , Stunnenberg Frank 
Published: September 2010

AbstractThe photochemistry (λ 300 nm) of the α‐oxo oxime ethers 1a and 2a has been studied with the objective of detecting any γ‐H abstraction. Direct irradiation of (Z)‐1a results only in (E)‐(Z) isomerization, whereas direct irradiation of the isomeric α‐oxo oxime ether 1b and the corresponding α‐diketone 1c leads mainly to cyclobutanol formation. The absence of cyclobutanol formation with 1a is ascribed to the higher angle of twist of the intercarbonyl‐iminyl angle of the reacting excited state of 1a, as compared with those of both 1b and 1c.The photodeuteration of the 7‐methyl hydrogens of 2a, using C2H3O2H as (co)‐solvent, is a very inefficient process (Φ 7.0 × 10−5), and that of the benzylic hydrogens of the related ketone 3a is even more inefficient (Φ ≤ 0.5 × 10−5). The inefficiency is ascribed mainly to the relatively low rate of γ‐H abstraction in the excited triplet (nπ*) state as well as to the very short life‐times of the ground state (Z)‐enols resulting from the relatively high rate of reketonization. The higher photodeuteration yield of the α‐oxo oxime ether 2a, as compared with the benzylic hydrogens of 3a, is ascribed to stabilization of the triplet 1,4‐diradical formed by γ‐hydrogen abstraction of the excited triplet (Z)‐2a, which results from electron delocalization and intramolecular hydrogen bonding.
NAD(P)H models XXII. Magnesium ion mediated acid catalysis of the reduction of imines by Hantzsch ester
Authors: van Niel J. C. G. , Kort C. W. F. , Pandit U. K. 
Published: September 2010

AbstractReduction of imines (2a‐e) derived from n‐butylamine and p‐substituted benzaldehydes, in the presence of magnesium perchlorate, by Hantzsch ester (1), in acetonitrile, proceeds via the corresponding iminium salts formed by protonation of the imines by [Mg(H2O)L5]2+ complexes. These complexes are produced by reaction of Mg2+ ions with water, which is associated with the solvent acetonitrile. Within the range 1.67 × 10−3‐26.11 × 10−3 M of added water, the rate of the reaction shows a direct dependence upon the concentration of water. Rates of reduction of the iminium perchlorates of 2a‐e exhibit a Hammett relationship with a ρ value of + 1.83.
Sulfur trioxide sulfodeprotonation of the rigidly bridged 1,6:8,13‐propane‐1,3‐diylidene[14]annulene
Authors: de Wit Peter , Kruk Cor , Cerfontain Hans 
Published: September 2010

AbstractThe sulfodeprotonation of 1,6:8,13‐propane‐1,3‐diylidene[14]annulene (1) with sulfur trioxide in dioxane and nitromethane at 20°C has been studied. Reaction of1with SO3in (2H8)dioxane yields initially only the 2‐sulfonic acid which is subsequently converted into about equal amounts of the 2,9‐ and 2,12‐disulfonic acid. Upon using 6.0 and 8.0 equiv. of SO3in (2H8)dioxane, the very rapid formation of the 2,9‐ and 2,12‐disulfonic acids is followed by a relatively slow conversion into a mixture of the 2,4,9‐, 2,4,12‐ and 2,5,9‐trisulfonic acids in a ratio ofca.3/3/2. Reaction of1with 8.5 equiv. of SO3in (2H3)nitromethane gave the 2,4,9,11‐, 2,4,9,12‐, 2,4,10,12‐ and 2,5,9,12‐tetrasulfonic acid in yields of 20, 39, 35 and 6%, respectively. The observed sulfonic acid isomer distributions are discussed in terms of the directing effects of the “ideal” [14]annulene and the sulfo substituent(s) already present.
The benzylic effect in nucleophilic attack on oxiranes
Authors: Lynas‐Gray Jack I. , Stirling Charles J. M. 
Published: September 2010

AbstractReactivities of 2‐phenyloxirane (4) and trans‐2,3‐diphenyloxirane (6) towards nucleophiles are comparable with those of non‐benzylic oxiranes; in aryloxiranes for which an antiperpendicular trajectory of the nucleophile orthogonal to the plane of the aryl ring is required, considerable increases in reactivity over non‐benzylic models are found.
13C NMR studies of p‐substituted nitrosobenzenes
Authors: Al‐Tahou Baheeja M. , Gowenlock Brian G. 
Published: September 2010

AbstractThe 13C NMR spectra of a wide range of monomeric para‐substituted nitrosobenzenes have been determined and the results related to a wide range of published data for other para‐disubstituted benzenes. It is shown that the nitroso substituent exercises a different pattern of effect for the 13C chemical shifts at the ipso C atom from at least twenty eight other substituents. It is noted that when the para substituent is a π‐donor, the nitroso group functions in a different manner from that operative when the para substituent is a π‐acceptor, a general possibility that has already been suggested in the recent literature.
Synthesis and spectroscopic study of 1,1′‐methylene‐2,2′‐pyrromethen‐5[1H]‐one and its 3,4‐dihydro and 2,3,4,6‐tetrahydro derivative
Authors: van Es J. J. G. S. , Koek J. H. , Erkelens C. , Lugtenburg J. 
Published: September 2010

AbstractThe Z‐syn‐locked 1,1′‐methylene‐2,2′‐pyrromethen‐5(1H]‐one 1, prepared in 45% yield in a one‐pot reaction from the previously reported 1,1′‐methylenebis(pyrrole‐5‐carbaldehyde) (8), exhibits a brilliant fluorescence with a high quantum yield (1.0) in contrast to the parent 2,2′‐pyrromethen‐5[1H]‐one systems. The λmax of emission and the quantum yield are solvent dependent. Catalytic reduction of 1 affords the 3,4‐dihydro derivative 2 in 80% and the 2,3,4,6‐tetrahydro derivative 3 in 80% and 95% yields, respectively. Compounds 2 and 3 exhibit no fluorescence, however 2 shows a very efficient photoFries‐type rearrangement. Advanced 1H NMR techniques had to be applied in order to obtain the complete analysis of the 1H NMR spectrum of 3, which showed the conformational details of its reduced bicyclic moiety.
Photochemistry of 3‐methyl‐1,2‐dihydronaphthalene
Authors: Laarhoven W. H. , Berendsen N. 
Published: September 2010

AbstractIrradiation of the title compound (6) with a broad spectrum lamp at room temperature afforded 2‐methylidene‐1,2,3,4‐tetrahydronaphthalene (8) and 2‐methylnaphthalene (7). Apart from 8, irradiation of 6 at −45°C also afforded 5‐methylbenzobicyclo[3.1.0]hex‐2‐ene (12) 1‐methylidene‐2‐(2‐tolyl)cyclopropane (13) as well as a small amount of 2‐methyl‐1,4‐dihydronaphthalene (14). Both 12 and 13 originate from the ring‐opened product of 6. Compound 14 is probably formed via a retro di‐π‐methane rearrangement from 12.Irradiation of 6 in n‐propylamine afforded the same photoproducts, 14 being the main one in this case.
The bonding of H2 in W(CO)5(H2), a reactive intermediate stabilized and identified in liquid xenon
Authors: Andréa Ronald R. , Vuurman Michael A. , Stufkens Derk J. , Oskam Ad 
Published: September 2010

AbstractLiquid Xenon (LXe) appears to be an ideal solvent for the study of reactive intermediates in photochemical reactions because of its complete inertness and transparency in both the IR and UV/Visible spectral regions. Photolysis of a H2‐doped solution of W(CO)6 in LXe at 193 K leads to the formation of W(CO)5H2 having CO stretching modes at 2098.4 (A21), 1972.2 (E) and 1970.5 cm−1 (A11) and v(H‐H) at 2707 cm−1. From a comparison of these CO stretching frequencies with those of other W(CO)5L complexes it is concluded that the W(dπ) → H2(σ*u) interaction is stronger than expected theoretically.
The meta photocycloaddition of fluoroarenes to cyclopentene
Authors: Osselton E. M. , Krijnen E. S. , Lempers E. L. M. , Cornelisse J. 
Published: September 2010

AbstractThe meta photocycloaddition of fluorobenzene and disubstituted fluoroarenes to cyclopentene has been investigated. From the effects of the various substituents and the varying product ratios it can be concluded that the reaction must proceed via a polar mechanism.
Photochemical reactions of 1‐acetyl‐3‐methylbicyclo[1.1.0]butane
Authors: Cerfontain Hans , Geenevasen Jan A. J. 
Published: September 2010

AbstractThe photochemistry of 1‐acetyl‐3‐methylbicyclo[1.1.0]butane in various solvents usingλ 254 and 300 nm radiation has been studied. In inert solvents, photoisomerization occurs with formation of 3 and 4 with subsequent photoconversion of 3 into 5. The (3 + 5)/4 ratios are significantly greater forλ 254 than forλ 300 nm radiation, illustrating direct reaction from the π* excited state(s). Additional photoreduction to 6 was observed forλ 300 nm in hydrogen‐donating solvents, especially in diisopropyl ether and toluene. In carbon tetrachloride, atλ 300 nm, mainly the HCl addition compound 10 is formed via ketone‐photosensitized decomposition of CCl4. Similarly, with methanol, 2‐propanol and water as solvent or addendum, the 1,3‐addition products 7–9 are obtained. Under all of these conditions, no photoproducts containing the intact bicyclo[1.1.0]butyl group were found, illustrating the high chemical reactivity of this severely strained group.Mechanisms for the formation of the photoisomerization, photoreduction and 1,3‐dipolar addition products are proposed.
Effect of pressure on the (2 + 2) cycloaddition of ethoxycyclopropane to tetracyanoethylene
Authors: Wiering Petrus G. , Steinberg Herbert 
Published: September 2010

AbstractThe pressure dependence of the (2 + 2) cycloaddition of ethoxycyclopropane 1 to tetracyanoethylene in various solvents has been studied.Only 3‐ethoxy‐1,1,2,2‐cyclopentanetetracarbonitrile 2 is formed in p‐dioxane and acetonitrile. The reaction in benzene, however, also gives rise to the ring‐opened enol ether 4E/Z, which rapidly reacts further with TCNE. The volume of activation is found to be −29.2 cm3/mole (CH3CN) and − 33.7 cm3/mole (p‐dioxane). These findings point to a two‐step cycloaddition mechanism involving a dipolar transition state.
The use of sulfenyl halides in the synthesis of mercapturic acids and their esters
Authors: Buijs Wim , van der Gen Arne , Eid Mohammed I. A. , Onkenhout Willem , Vermeulen Nico P. E. 
Published: September 2010

AbstractA new method for the synthesis of mercapturic acids (N‐acetyl‐S‐substituted‐L‐cysteines), based on the addition of sulfenyl halides to olefins, is described. Alkenes and alkynes of widely different structure have been converted in this way into fully characterized mercapturic acids and their methyl esters.
Synthesis and reactions of 3‐alkoxy‐2H‐azirines
Authors: Ghosez L. , Sainte F. , Rivera M. , Bernard‐Henriet C. , Gouverneur V. 
Published: September 2010

Abstract3‐Alkoxy‐2H‐azirines 4 have been prepared by treatment of enol ethers 6 with iodine azide followed by base‐catalysed elimination of HI and thermolysis of the resulting vinyl azide 5. Azirines 4 readily undergo electrophilic additions, to yield products resulting from cleavage of either the N(1)‐C(3) or the N(1)‐C(2) bond. Reaction of 4 with trimethylsilyl cyanide yields highly functionalized aziridines 12. Thermolysis of 4 produces C‐alkoxy‐N‐vinylmethanimines.
Synthesis of 5‐deazaflavin adenine dinucleotide (5‐dFAD) using a modified triester approach
Authors: Smit P. , Stork G. A. , van der Plas H. C. , den Hartog J. A. J. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractStarting from D‐ribose and 3,4‐xylidine, a fifteen‐step synthesis is described for the preparation of 5‐dFAD (18). The synthesis involves as key intermediates, 5‐deazariboflavin (8), its 2′,3′,4′‐tris‐O‐(tetrahydropyranyl) derivative (12) and 2′,3′,4′‐tris‐O‐(tetrahydropyranyl)‐5′‐O‐(morpholinophosphonyl)‐5‐deazariboflavin (15).
4,5α‐epoxy‐3‐methoxy‐8β‐nitro‐6β, 14β‐ethenomorphinan, a novel type Diels‐Alder adduct from 6‐demethoxy‐17‐formylnorthebaine and nitroethene (Chemistry of opium alkaloids, part XXIII)
Authors: Prazeres M. A. , Peters J. A. , Linders J. T. M. , Maat L. 
Published: September 2010

Abstract4,5α‐Epoxy‐3‐methoxy‐8β‐nitro‐6β, 14β‐ethenomorphinan (5) was isolated as one of two major cycloaddition products of 6‐demethoxy‐17‐formylnorthebaine (3) and nitroethene. Structure elucidation was mainly based on 1H NMR data.
Crystal and Molecular Structure of 1,2‐Diphenylcyclopentene, C17H16. A redetermination
Authors: Smits J. M. M. , Beurskens Paul T. , Laarhoven W. H. 
Published: September 2010

AbstractThe structure of the title compound was determined by X‐ray analysis, using CuKα radiation, graphite crystal monochromator, λ=1.5418 Å, C17H16, Mr =220.31, monoclinic, space group P21, a=9.0270(9), b=9.5267 (16), c=8.0327(6) Å,β=112.366(7)°, V=638.8 Å3, Z=2, Dc=1.145 Mg/m3, μ(MoKα)=4.92 cm−1, F(000)=236.0, T=290 K. Final conventional R‐factor = 0.044, Rw =0.063 for 2222 unique reflections and 201 variables. The structure was solved by MULTAN.
Crystal and Molecular Structure of Ethyl‐α((E)‐hydroxyimino)‐β‐(2(α,α‐dimethylallyl) indol‐3‐yl)propanoate, C18H22N2O3.1/6 CH2CL2
Authors: Bosman W. P. , Beurskens Paul T. , Smits J. M. M. , Plate Ralf , Ottenheijm Harry C. J. 
Published: September 2010

AbstractThe structure of the title compound was determined by X‐ray analysis, using MOKα radiation, graphite crystal monochromator, λ=0.71069 Å, C18H22N2O3. 1/6 CH2Cl2, Mr=376.53, monoclinic, space group P21/c, a=12.297 (11), b=17.781(6), c=16.612(3) Å,β=93.91(3)°, V=3624(3) Å3, Z=8, Dc=1.35 Mg/m3, μ(MoKα)=1.6 cm−1, F(000)=1399.0, T=290 K. Final conventional R‐factor = 0.096, Rw=0.119 for 3060 unique reflections and 419 variables. The structure was solved by an orientation and translation search on a known fragment and expanded with DIRDIF.
On the relative stabilities of zeolitic silicas
Authors: Ooms G. , van Santen R. A. 
Published: September 2010

AbstractA simple quantum‐chemical calculation method has been used to obtain a first estimate of the relative stabilities of zeolitic silicas. When applied to dealuminated faujasite, mordenite and ZSM‐5, the method indicated faujasite to be less stable than mordenite and ZSM‐5. However, the calculated differences in heat of formation between the dealuminated zeolites are very small. Hence, care must be taken in drawing any definite conclusions, particularly in view of the rather approximate nature of the calculation method.
Aromatic isomerizations and related reactions. Part 6 Reactions of the tetra‐ and pentamethylbenzenesulfonic acids and hexamethylbenzene in concentrated sulfuric acid; the mechanism of the Jacobsen reaction
Authors: Koeberg‐Telder Ankie , Cerfontain Hans 
Published: September 2010

AbstractThe chemical behaviour of the sulfonic acids of pentamethylbenzene (PMB) and the three tetramethylbenzenes (TeMB's) in concentrated aqueous sulfuric acid has been studied quantitatively using 1H and 13C NMR and UV spectroscopy. PMB‐sulfonic acid yields (protonated) hexamethylbenzene (HMB) and the 2,3,4,5‐ and 2,3,4,6‐TeMB‐1‐sulfonic acids in an initial ratio of 9/1/8 up to a substrate conversion of 36%; the ratio of HMB to the TeMB‐1‐sulfonic acids remains 1/1 and the only subsequent reaction is the relatively slow conversion of the 2,3,4,6‐ into the 2,3,4,5‐TeMB‐1‐sulfonic acid which is the only stable TeMB‐1‐sulfonic acid isomer in concentrated sulfuric acid.2,3,5,6‐TeMB‐1‐sulfonic acid yields, as initial products, 2,3,5‐ and 2,4,5‐trimethylbenzene(TrMB)‐1‐sulfonic acid together with PMB‐1‐sulfonic acid in a ratio of ca. 1/3/4. The subsequent products are the 2,3,4,6‐ and 2,3,4,5‐TeMB‐1‐sulfonic acids, of which the former slowly isomerizes to the latter, together with some HMB.2,3,4,6‐TeMB‐1‐sulfonic acid yields the stable 2,3,4,5‐isomer. It is proposed that the conversion proceeds via inter‐molecular trans‐methylations involving 1,3,5‐TrMB and PMB as intermediates, the concentrations of which, however, are below the limits of NMR detection.Based on (i) the desulfonation‐sulfonation equilibrium data of the TrMB‐, TeMB‐ and PMB‐sulfonic acids, (ii) the strong rate decrease for the conversion of both 2,3,4,6‐ and 2,3,5,6‐TeMB‐1‐sulfonic acid in 98.4% H2SO4 in the presence of added cyclohexane and (iii) the very strong electron‐withdrawing and meta‐directing effect of the SO3−/SO3H substituent, it is proposed that all the conversions proceed inter‐molecularly, that the trans‐methylating reagent is the polymethylbenzene (and not the corresponding sulfonate) and that the substrate undergoing methylation is most likely to be once again the polymethylbenzene rather than its sulfonate ion.
Conformational effects of through‐bond interaction in N‐aryl‐piperidine derivatives
Authors: Krijnen B. , Beverloo H. B. , Verhoeven J. W. 
Published: September 2010

AbstractThrough‐bond interaction in an N‐aryl‐piperidine derivative carrying an electronegative substituent at C‐4 is found to stabilize axial arrangement of the aryl group, which demonstrates the possibility of long‐range stereoelectronic conformational control.
The chemistry of D‐gluconic acid derivatives. Part 1: Synthesis of 3,4;5,6‐di‐O‐isopropylidene‐D‐glucitol and 2,3;4,5‐di‐O‐isopropylidene‐aldehydo‐D‐arabinose from D‐glucono‐1,5‐lactone
Authors: Regeling Henk , de Rouville Egbert , Chittenden Gordon J. F. 
Published: September 2010

AbstractAcid‐catalysed isopropylidenation of D‐glucono‐1,5‐lactone with 2,2‐dimethoxypropane yields methyl 3,4;5,6‐di‐O‐isopropylidene‐D‐gluconate. Convenient syntheses of the title compounds from this ester by reduction and oxidation sequences, together with the characterisation of the products and intermediates are described.
A specific 2,4‐disubstituted‐adamantane interaction with plasma‐grown aluminium oxide. An inelastic‐electron‐tunnelling spectroscopy study
Authors: Meijer E. W. , Raas M. C. , van Velzen P. N. T. 
Published: September 2010

AbstractThe interaction of several mono‐ and disubstituted adamantanes with plasma‐grown aluminium oxide has been studied using inelastic‐electron‐tunnelling (IET) spectroscopy. The IET spectra evidence the chemisorption of 2,4‐adamantanedione (1) onto the aluminium oxide surface as the carboxylate anion of bicyclic acid ketone 2, which is formed by ring opening of the β‐diketone. In the case of 4‐hydroxy‐2‐adamantanone (3), no ring opening to the corresponding bicyclic acid (4) is observed. 3 is chemisorbed as aluminium alkoxide through condensation. Stabilization by additional hydrogen bonding between the aluminium oxide and the keto group seems to be required since 1‐adamantanol, 2‐adamantanol and 2‐adamantanone do not adsorb onto the aluminium oxide. Even 5‐hydroxy‐2‐adamantanone is not bonded to the surface, indicating the necessity of a specific 2,4‐disubstituted adamantane bidentate interaction with aluminium oxide.
Photochemistry of estra‐5,7‐diene‐3β,17β‐diol 17‐acetate and its 9,10‐seco isomer, 10‐desmethyl analogues of pro‐ and previtamin D. 1. “Reversible” isomerization reactions
Authors: Koolstra R. B. , Cornelisse J. , Jacobs H. J. C. 
Published: September 2010

AbstractIn analogy with the photochemistry of 7,8‐didehydrocholesterol (provitamin D), irradiation of the 10‐desmethyl steroid estra‐5,7‐diene‐3β,17β‐diol 17‐acetate leads to a photoequilibrated mixture of steroid‐5,7‐dienes and 9,10‐seco‐5(10),6,8‐trienes. In addition, a thermally unstable bicyclo[2.2.0]hexene derivative is found. From the composition of the quasi‐photostationary state, the ratios of the quantum yields of the various interconversions are estimated. Differences with the photochemistry in the 10‐methyl series are discussed in relation to conformational differences.
The influence of substituents on the geometry of the cyclopropane ring: III. The molecular and crystal structure of phenylcyclopropane
Authors: de Boer J. S. A. M. , Loopstra B. O. , Stam C. H. 
Published: September 2010

AbstractPhenylcyclopropane, C6H5C3H5, is monoclinic, with space group Pa, a = 15.761(4), b = 7.748(2), c = 5.854(2) Å, β = 103.01(1)°. V = 696.5(4) Å3 (‐ 100°C). Z = 4. The final R for 1192 independent reflections is 0.039. The two molecules in the asymmetric unit are very similar, the plane of the benzene ring bisecting the cyclopropane ring. The average distal bond length in the cyclopropane ring is 1.502(7) Å; the average vicinal length is 1.520(5) Å (corrected for libration).
An improved procedure for the acetalisation of alcoholic hydroxyl functions
Authors: Roelen H. C. P. F. , Ligtvoet G. J. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractAcetalisation of 3′,5′‐di‐O‐acetyluridine in DMF with 4,4‐dimethoxytetrahydro‐4H‐pyran and 4,4‐dimethoxytetrahydro‐4H‐1‐thiopyran in the presence of trimethylsilyl chloride (TMSiCl) afforded, after removal of the acetyl groups, 2′‐O‐(4‐methoxytetrahydropyranyl)‐uridine and its sulfur analogue, respectively. It was also established that a 3′,5′‐O‐(tetraisopropyldisiloxane‐1,3‐diyl) protected ribonucleoside was rapidly isomerised into the corresponding 2′,3′‐isomer using the TMSiCl promoted acetalisation method.
Synthesis of diphosphorylated and diphosphonylated Lipid A monosaccharide analogues via phosphite intermediates
Authors: Westerduin P. , Veeneman G. H. , van Boom J. H. 
Published: September 2010

AbstractThe synthesis of two Lipid A monosaccharide analogues, 3‐O‐palmitoyl‐2‐deoxy‐2‐palmitamido‐α‐D‐glucopyranose 1,4‐diphosphate (1) and the corresponding 1,4‐bis(1H‐phosphonate) (2), is described. The introduction of the phosphate functions was achieved via phosphitylation of the anomeric and non‐anomeric hydroxyl groups with the monofunctional phosphitylating reagents benzyl 2‐cyanoethyl N,N‐diethylphosphoramidite (9) and salicyl phosphochloridite (10). Oxidation of the intermediate phosphite triester and subsequent removal of all the protective groups afforded the target molecules 1 and 2.
Empirical force field calculations. Part 28. Conformations and pseudorotations of 1,3‐dioxolane and some methyl‐substituted derivatives
Authors: van Duin M. , Hoefnagel M. A. , Baas J. M. A. , van de Graaf B. 
Published: September 2010

AbstractThe conformations and pseudorotations of 1,3‐dioxolane (1), cis‐ and trans‐4,5‐dimethyl‐1,3‐dioxolane (2 and 3) and the corresponding 2,2‐dimethyl derivatives (4, 5 and 6) have been studied with molecular mechanics using the MM2 force field. Free pseudorotation occurs in 1 and 4 (ΔE = 1.5 kJ/mol) and pseudolibration in 2, 3, 5 and 6 (ΔE = 6, 7, 11 and 14 kJ/mol, respectively). The steric energies of 3 and 6 are lower than those of 2 and 5 since the 4‐ and 5‐methyl groups can both occupy a pseudo‐equatorial position in the minimum energy conformation of the trans isomers. Estimates of ΔH°f (25°C, gas, kJ/mol) are: 2, ‐ 376.1; 3, ‐ 380.5; 4, ‐ 387.2; 5, ‐ 464.4; 6, ‐ 470.1. Vicinal proton coupling constants were calculated from the appropriate torsion angles and averaged over the pseudorotation circuit. They are in good agreement with experimental values. The 1,3‐dioxolanes can be used as model compounds for borate monoesters of vicinal diols. The 13C chemical shifts of C(2) in 1,3‐dioxolanes correlate well with the 11B chemical shifts in the corresponding borate monoesters.