bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reactions of cumulated and conjugated dienes with sulfur trioxide
Authors: Schonk Ruud M. , Bakker Bert H. , Cerfontain Hans 
Published: September 2010

AbstractThe reactions of a series of cumulated (1a‐5a) and conjugated alkadienes (8a‐13a) with sulfur trioxide have been studied in the temperature range of −60 to 25°C using dichloromethane as solvent and 1.5 equiv of dioxane as reactivity moderator. Reaction of tetramethylallene (1a) at low temperature yielded the β‐sultone 1b, which at 0°C was slowly converted into 2,4‐dimethyl‐1,3‐pentadiene‐3‐sulfonic acid (1f). This conjugated dienesulfonic acid, in the presence of additional SO3, at 0°C, was rapidly converted into the unsaturated δ‐sultone 1g. Reaction of 1,2‐ cyclononadiene (5a) with SO3, formed an exception to the generally observed formation of the unsaturated δ‐sultones g, as at low temperatures a 1:1 mixture of 2‐cyclononene‐2,1‐sultone (5b) and the corresponding carbyl sulfate (5d) was formed. These products at 0°C were both converted into the same alkadienesulfonic acid, viz. 6. Upon using an excess of SO3, 6 was rapidly converted into 3‐cyclononene‐1,2‐sultone‐3‐sulfonic acid (7).Reaction of the conjugated alkadienes 8a‐13a with sulfur trioxide led to the formation of the similar unsaturated δ‐sultones 8g‐13g, as observed upon starting with the cumulated dienes 1a‐5a. The reactions of SO3 with the conjugated alkadienes 9a‐12a clearly demonstrate that the formation of the δ‐sultones proceeds non‐stereospecifically. The formation of the unsaturated δ‐sultones from the alkadienes 1a‐5a and 8a‐13a is, therefore, suggested to proceed via a two‐step reaction, viz. An initial [2s + 2s] cycloaddition, followed by very fast conversion of the resulting β‐sultone into the unsaturated δ‐sultone g.
Sulfonation of 1‐ and 2‐naphthol and their methanesulfonate esters with sulfur trioxide. The influence of initial sulfation on the sulfo‐product composition
Authors: Ansink Harold R. W. , Zelvelder Erwin , Cerfontain Hans 
Published: September 2010

AbstractThe sulfonation of 1‐ and 2‐naphthol with sulfur trioxide in C2H3NO2 has been studied by using 1H NMR. 1‐Naphthol (1) yields, upon reaction with 1.0 mol‐equiv of SO3, a mixture of 2‐ and 4‐sulfonic acids (2‐ and 4‐S); upon increasing the reaction temperature, the relative amount of 2‐S increases. Upon reaction with 4.0 mol‐equiv of SO3, the initially observed products are the hydrogen sulfate 1‐O,2,4‐S3, and some corresponding sulfonic anhydrides. After prolonged reaction times, some 1‐O‐4,7‐S3, is formed.2‐Naphthol (3), upon reaction with 1.0 mol‐equiv of SO3, yields a 85: 15 mixture of 1‐S and 8‐S, whereas upon reaction with 2.0 mol‐equiv of SO3, a 8: 14: 78 mixture of the 5‐S, 6‐S and 8‐S are formed. Sulfonation of 3, either by (i) reaction with 1.2 and, subsequently, an additional 2.0 mol‐equiv of SO3, or (ii) by direct addition of 4.0 mol‐equiv of SO3, yields a mixture of the carbyl sulfates 5‐5‐S and 5‐6‐S and the hydrogen sulfate 3‐O,6,8‐S3, the relative yield depending on the method used.The results are discussed in terms of initial formation of the corresponding naphthyl hydrogen sulfates and on the basis of a comparison with the reactions of 1‐ and 2‐naphthyl methanesulfonates, the chosen model compounds for the hydrogen sulfates, with SO3.
Conformational analysis of cis‐fused eudesm‐11‐en‐4‐ols
Authors: Kesselmans R. P. W. , Wijnberg J. B. P. A. , Schrijvers R. , Sudhölter E. J. R. , de Groot Ae. 
Published: September 2010

AbstractThe conformational behaviour of the four cis‐fused stereoisomers 1–4 of eudesm‐11‐en‐4‐ol has been investigated using NMR spectroscopy. In addition, the conformational behaviour of these compounds has been simulated with molecular‐mechanics calculations using the MM2(87) force‐field program. Comparison of the results obtained from NMR analysis and MM2 calculations shows that the outcome of both methods agree very well.
Coordination compounds of tripeptides and pentapeptides containing L‐histidyl residues. Studies towards structural models for the active site of copper proteins
Authors: Hulsbergen F. B. , Reedijk J. 
Published: September 2010

AbstractFive small, completely protected, L‐histidyl(NτBzl)‐containing peptides, were synthesized and characterized by NMR spectroscopy, i.e., R‐Ala‐His(Nτ‐Bzl)‐Ala‐R′ (1), R‐His(Nτ‐Bzl)‐Ala‐Ala‐Ala‐Met‐R′ (2), R‐His(Nτ‐Bzl)‐Ala‐Ala‐Ala‐His(Nτ‐Bzl)‐R′ (3), R‐His(Nτ‐Bzl)‐Ala‐His(Nτ‐Bzl)‐Ala‐His(Nτ‐Bzl)‐R′ (4), R‐His(Nτ‐Bzl)‐Ala‐His(Nτ‐Bzl)‐R′ (5), in which: R is phenylacetyl (PhCH2CO‐), R′ is phenylamino (‐NHPh); Bzl is benzyl (PhCH2‐).It has been shown that benzylation of histidine residues takes place at the Nτ atom of the imidazole. The resulting peptide derivatives appear to be good ligands for CoII, ZnII and CuI. Titrations of zinc chloride solutions towards peptide solutions (in dmso‐d6, dimethyl sulfoxide followed by NMR spectroscopy show the formation of the two species [Zn(NπHis)2Cl2] and [Zn(NπHis)(dmso)Cl2]. Copper(I)‐chloride titrations result in formation of trigonal planar and tetrahedral complexes (in dmso‐d6). Zinc, copper and cobalt trifluoromethanesulfonates were also investigated, and corresponding tetrahedral species with additional dmso ligands replacing chloride were obtained. In addition, octahedral complexes have been found, as shown for cobalt(II) using ligand‐field spectroscopy.Conductivity experiments of zinc chloride complexes in dmso and chloroform indicate non‐electrolytes. Their very low conductivity in methanol indicates only slight dissociation of chloride, in agreement with a tetrahedral geometry for zinc(II). For [Co(NπHis)2Cl2], the UV‐VIS adsorption spectra in dmso and in the solid state (diffuse reflection) are comparable, indicating tetrahedral geometry, with a CoN2Cl2 chromophore.
Self‐assembling chiral metallo‐clefts; synthesis and molecular structure of N,N′‐bis(12H‐benzo[α]xanthen‐12‐ylidene)‐1,2‐ethanediamine zinc(II)‐dichloride complex
Authors: Barf Tjeerd , Jansen Johan F. G. A. , van Bolhuis Fré , Feringa Ben L. , Spek Anthony L. 
Published: September 2010

AbstractBulky ligands for cleft‐type metal complexes were synthesized from thio ketones and diamines in yields varying from 20–80%. A molecular structure determination of one ligand N,N′‐bis(12H‐benzo[a]‐xanthen‐12‐ylidene)‐1,2‐propanediamine (19) was performed. A metallocleft was constructed by a self‐assembling process with zinc(II) chloride. A crystallographic study of this zinc complex (24) revealed surprisingly that an anti‐syn inversion of the imine moieties of the ligand had taken place during complexation.
Rapid charge migration within 1,4‐benzoquinone stacks in the solid phases of 2,5‐Di‐n‐decoxy‐1,4‐benzoquinone
Authors: Keegstra E. M. D. , Zwikker J. W. , Jenneskens L. W. , Schouten P. G. , de Haas M. P. , Warman J. M. , Schouten A. , Kooijman H. , Spek A. L. 
Published: September 2010

AbstractTemperature dependent, radiation‐induced conductivity measurements of 2,5‐di‐n‐decoxy‐1,4‐benzoquinone (1) unambiguously show that self‐assembly of the 1,4‐benzoquinone moieties into stacks is a prerequisite for rapid electron and/or hole migration.
A remarkable halogen‐zinc exchange reaction; X‐ray crystal structure of (2‐iodozincio‐1,3‐xylylene)‐15‐crown‐4
Authors: Gruter Gert‐Jan M. , Akkerman Otto S. , Bickelhaupt Friedrich , Smeets Wilbert J. J. , Spek Anthony L. 
Published: September 2010

AbstractAn unprecedented halogen‐metal exchange was observed in the reaction between (2‐iodo‐1,3‐xylylene)‐15‐crown‐4 and diethylzinc, which resulted in the formation of (2‐iodozincio‐1,3‐xylylene)‐15‐crown‐4. An X‐ray crystal structure of this product is presented.
Polymer‐supported solution synthesis of a heptaglucoside having phytoalexin elicitor activity
Authors: Verduyn R. , van der Klein P. A. M. , Douwes M. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractAn efficient synthesis of methyl heptaglucoside 2 using poly(ethyleneglycol)monomethyl ether as a polymer support is described. Elongation of the acceptor 11, anchored via a succinoyl linkage to PEG, with the appropriate glycosyl donors 4–6 and intermittent protective group manipulations gave fully protected heptamer 18. Deprotection of 18 furnished, after purification as its peracetate, title compound 2 in a good overall yield.
Potential usefulness of sugar 1,2 thio ortho esters in iodonium‐promoted glycosidation
Authors: Zuurmond H. M. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractSugar 1,2 thio ortho esters can be condensed with terminal glycosyl acceptors using iodonium‐ion sources (IDCP and NIS/TfOH) as activators. IDCP‐ or NIS/TfOH‐assisted glycosidation of sugar 1,2 thio ortho esters with primary hydroxyl groups of “armed” or “disarmed” ethyl (phenyl) 1‐thioglycosides gave the respective disaccharides having 1,2 ortho ester or 1,2 trans interglycosidic linkages.
Synthesis of 2,3‐dihydro‐I H,4 H, 6 H‐furo[3,4‐b]pyrrolo[1,2‐a]quinoline‐6a(7H)‐carbonitrile; a novel type of intramolecular tetrahydrofuran formation
Authors: Verboom Willem , Morzherin Yury , Kelderman Erik , Engbersen Johan F. J. , Reinhoudt David N. , van Hummel Gerrit J. , Harkema Sybolt 
Published: September 2010

AbstractAppropriately 4‐substituted 1,2,3,3a,4,5‐hexahydro‐3a‐(methoxymethyl)pyrrolo[1,2‐a]quinolines 3 cyclize to 2,3‐dihydro‐1 H,4H,6H‐furo[3,4‐b]pyrrolo[1,2‐a]quinoline‐6a(7H)‐carbonitrile (5) upon heating in polar solvents, the reaction being accelerated by lithium bromide. The formation of the annulated tetrahydrofuran ring of 5 takes place via intramolecular attack of the oxygen atom of the methoxymethyl substituent at C‐3a on the electrophilic carbon atom at C‐4. The structure of 5 was confirmed by single‐crystal X‐ray structure determination.
Synthesis of 7‐substituted 6‐demethoxythebaines and Diels‐Alder reaction of 7‐methoxy‐5β‐methyl‐6‐demethoxythebaine (chemistry of opium alkaloids, part XLI)
Authors: Woudenberg R. H. , Meuzelaar G. J. , Maat L. 
Published: September 2010

AbstractMesylation of 7‐acetoxyneopine(4), followed by reductive cleavage of the acetyl group gave 6α‐O‐mesyl‐7α‐hydroxyneopine(6), in which the hydroxyl group was protected as a methoxymethoxy group. Elimination of the mesyl ester yielded 7‐(methoxymethoxy)‐6‐demethoxythebaine(7). For the 5β‐methyl analogue, we started from 6‐O‐acetyl‐7α‐hydroxy‐5β‐methyl‐neopine(5), which was converted into9via hydroxyl protection as a methoxymethoxy group and removal of the acetyl group. Mesylation and elimination gave 7‐(methoxymethoxy)‐5β‐methyl‐6‐demethoxythebaine(10). Hydrolysis of7and10afforded the salutaridine analogue11and 5β‐methyl‐6‐deoxyneopin‐7‐one(12), which were easily converted into the 7,7‐dimethoxy‐6‐deoxyneopine analogues13and14. Elimination of methanol from14yielded the desired diene15. Diels‐Alder reaction of15with ethyl acrylate yielded exclusively the 8β‐substituted 6β,14β‐ethenomorphinan16, due to α‐face approach. Cycloaddition of diene15with maleic anhydride gave the 6α, 14α‐ethenoisomorphinan17and the 6β,14β‐ethenomorphinan18in a ratio of 5: 4. The outcome of the Diels‐Alder reactions is discussed in relation to the substituents at the 5β‐ and 7‐positions combined with an asynchronous cycloaddition mechanism.
Unexpected phenomena in glycosylations of acceptors with L‐idose configuration
Authors: Spijker Nynke M. , Basten Jan E. M. , van Boeckel Constant A. A. 
Published: September 2010

AbstractFor the synthesis of Galß(1 → 4)IdoA disaccharides 1, several glycosylations of L‐iduronic acid derivatives 5 and 13 and of L‐idopyranose derivative 21 were performed with differently protected D‐galactopyranosyl donors under various conditions. It was found that these coupling reactions mainly led to the formation of the undesired α‐interglycosidic linkage, even when the donor contained a participating group at C‐2. On the other hand, coupling of the corresponding D‐glucopyranosyl donor 19 with 13 led to a much higher β/α ratio (2/1). By changing the conformation of the acceptor into the 1,6‐anhydro‐L‐idopyranose acceptor 23, 90% of the desired β‐coupled disaccharide was obtained in the glycosylation with galactopyranosyl donor 12. Finally it was found that the α/β ratio of the condensation with 25, promoted by an insoluble silver salt, was influenced in an unusual way by the substituents at the galactosyl bromide.
The influence of substituents on the geometry of the cyclopropane ring. VII The molecular and crystal structures of bicyclopropylidene (C3H4C3H4) and (dicyclopropylmethylene)cyclopropane [(C3H5)2CC3H4]
Authors: de Boer J. S. A. M. , Stam C. H. 
Published: September 2010

AbstractCrystals of bicyclopropylidene grown from the liquid are monoclinic, space group P21/n, a = 4.9744(3), b = 12.4870(8); c = 4.0366(3) Å, β = 95.077(7)° (173 K), Z = 2. The final R for 450 independent observed reflections is 0.036.Crystals of (dicyclopropylmethylene)cyclopropane grown from the liquid are monoclinic, space group P21/a. a = 16.781(2), b = 7.260(1), c = 13.665(1) Å, β = 99.28(1)° (123 K), Z = 8. The final R for 2592 independent observed reflections is 0.046.The dimensions of the cyclopropylidene moiety in the molecules of both compounds are very similar. The (average) lengths of the distal bonds are 1.549 and 1.547 Å, respectively, and the (average) length of the vicinal bonds is 1.472 Å in both molecules. The average dimensions of the cyclopropane rings in the molecules of the second compound are 1.505 Å for the distal and 1.513 Å for the vicinal bonds. There is a significant difference between the lengths of the double bonds in the two compounds [1.307(2) and 1.327(2) Å, respectively; all distances corrected for librational motion of the molecules].
Reaction of C60, C70, C76, C78, and C84 with ozone at 23.5°C
Authors: Heymann Dieter , Chibante L. P. Felipe 
Published: September 2010

AbstractC60, C70, C76, C78, and C84 dissolved in toluene, were treated at 23.5°C with ozone. The concentrations of all five fullerenes decreased with increasing dose of ozone, but C60, C76, C78, and C84 transformed significantly faster than C70. Oxides of C60 and C70, but not of the other fullerenes, were observed in the ozonated solutions. We assume that all five fullerenes form molozonides, which swiftly lose molecular oxygen to form oxides. We assume further that the molozonide always forms at an interpentagonal bond. The π‐bond orders calculated by Taylor for such bonds may explain the faster ozonation of C76, C78, and C84, but probably not of C60. We suggest that the “equatorial belt” of 15 hexagons of C70, with its relatively high π density may be the cause for the slower rate of ozonation of C70.
New pyridinecarbonitriles from fluoro arylpropenones
Authors: Mishriky N. , Asaad F. M. , Girgis A. S. , Ibrahim Y. A. 
Published: September 2010

AbstractThe facile synthetic approaches to 3‐pyridinecarbonitriles are described. The first approach involves the base‐catalyzed transformation of 4‐hydroxy‐1,1‐cyclohexanedicarbonitrile 2a into 4a, b. The other route involves the base‐catalyzed multi‐step one‐pot reaction of aryl methyl ketones with the appropriate arylidenemalononitriles 6, 11a, b. Careful study of the synthesis of 2a, b from 1a, b revealed the importance of controlling the reaction conditions. Thus, 1,7‐dioxo‐4,4‐heptanedicarbonitriles 3a, b or 3‐pyridinecarbonitrile 4a were obtained in addition to the desired 2a, b under different basic conditions.
Crystal Structure and Silver Ion Complexation of a Novel Porphyrazine Substituted with four Dithiacrown ether Rings
Authors: van Nostrum Cornelus F. , Benneker Franciscus B. G. , Nolte Roeland J. M. , Veldman Nora , Spek Anthony L. , Schouten Arend‐Jan 
Published: September 2010

AbstractThe synthesis of magnesium porphyrazines substituted with sulfur‐containing 15‐crown‐5 and 18‐crown‐6 macrocycles is reported as well as the single crystal structure of the 18‐crown‐6 substituted porphyrazine; the larger crown ether compound is shown to form dimers with Ag+ ions, unlike the porphyrazine with the smaller crown ether rings.
Synthesis and Physical Properties of Highly Ca2+‐Tolerant Disodium 2‐(Sulfatomethyl)‐1‐Alkylsulfate Surfactants
Authors: Kooreman Peter A. , Engberts Jan B. F. N. 
Published: September 2010

AbstractThe synthesis, critical micelle concentrations (CMC) and Krafft temperatures (TKrafft) of a series of disodium 2‐(sulfatomethyl)‐1‐alkylsulfates (2a‐d) are presented, with alkyl being n‐tetradecyl (C14), n‐hexadecyl (C16), n‐octadecyl (C18) and n‐eicosyl(C20). The surfactants exhibit a large Ca2+‐tolerance in aqueous solutions.
Microemulsions as reaction media. Self‐organizing assemblies in an environmental cleanup problem
Authors: Menger F.M. , Park H. 
Published: September 2010

AbstractA microemulsion system has been developed that simultaneously destroys three environmental contaminants by combined oxidative/hydrolytic pathways. The method is rapid, cheap, and mild. No special equipment (stirrer, heater, photolyzer, etc.) is required. Self‐organization converts a seemingly intractable 8‐component mixture into a useful system, a tactic discovered by living cells long ago.
Organonickel(II) complexes containing aryl ligands with chiral pyrrolidinyl ring systems; syntheses and use as homogeneous catalysts for the Kharasch addition reaction
Authors: van de Kuil Lucia A. , Veldhuizen Yvonne S. J. , Grove David M. , Zwikker Jan W. , Jenneskens Leonardus W. , Drenth Wiendelt , Smeets Wilberth J. J. , Spek Anthony L. , van Koten Gerard 
Published: September 2010

AbstractNew chiral organonickel(II) complexes 3a‐d have been synthesized containing monoanionic terdentate ligands of the type 2,6‐bis[(1‐pyrrolidinyl)methyl]phenyl. Chirality is introducedmagnified imageat the nitrogen donor atoms, which are part of the pyrrolidinyl ring systems, by placing substituents on the 2 or 5 positions of the rings. The complexes have been characterized variously by 1H‐ and 13C‐NMR spectroscopy, UV/Vis spectroscopy and X‐ray crystallography.Crystals of 3b are monoclinic, space group P21, with a = 11.572(2), b = 11.804(2), c = 13.249(3) Å, β = 107.00(2)°, Z = 4, final R = 0.043 for 3043 observed reflections. Crystals of 3c are tetragonal, space group P412121, with a = b = 12.2957(14) Å, c = 26.418(3) Å, Z = 8, final R = 0.052 for 1479 observed reflections. Crystals of 3d are tetragonal, space group P412121, with a = b = 11.0869(5), c = 21.718(2) Å, Z = 4, final R = 0.046 for 1469 observed reflections.The catalytic ability of the nickel complexes in the addition reaction of polyhalogenated compounds with alkenes (Kharasch addition) is markedly influenced by the geometry around the nickel atom and only 3a and 3b prove to be effective catalysts. The highest enantiomeric excesses of 16‐17% obtained with 3b and L‐menthyl methacrylate in this catalytic reaction indicate that the C2 chiral fence produced by the Me‐substituted pyrrolidinyl rings is not very effective for the transfer of chiral information.
A LHASA analysis of taxol
Authors: van Rozendaal Erik L. M. , Ott Martin A. , Scheeren Hans W. 
Published: September 2010

AbstractA retrosynthetic analysis using the computer program LHASA of the promising antitumor agent taxol (1) is described, which resulted in a synthetic route with the following key steps: an intramolecular Diels‐Alder reaction generating the AB rings, and the coupling reactions of the required diene and dienophile with a CD‐ring fragment. The feasibility of the route is studied by comparing the LHASA analysis with related chemistry from the literature. Finally, a critical discussion about the usability of the LHASA program for the planning of complex organic molecules is given.]
Synthesis of 3‐alkenylcephalosporins using an epoxide mediated wittig reaction
Authors: de Vroom Erik , van der Wal Anton , Lugtenburg Johan 
Published: September 2010

AbstractThe synthesis of 3‐alkenyl cephalosporins 5 using an epoxide mediated Wittig reaction is described. Reduction of the 3′‐triphenylphosphonium cephalosporin‐1‐oxide 4 followed by condensation with acetaldehyde in the presence of 1,2‐epoxybutane gave, after purification, the 3‐propylidene derivative 5 (R1=CH3) in 39% yield.
Synthesis of L‐histidine specifically labelled with stable isotopes
Authors: Cappon J. J. , Witters K. D. , Baart J. , Verdegem P. J. E. , Hoek A. C. , Luiten R. J. H. , Raap J. , Lugtenburg J. 
Published: September 2010

Abstract(2′‐13C)‐, (1′‐15N)‐ and (3′‐15N)‐L‐Histidine were prepared according to a synthetic scheme that allows the 13C or 15N labelling of all carbon and nitrogen positions or any combination of positions. A 1,5‐disubstituted imidazole ring was constructed via condensation of tosylmethyl isocyanide with 3‐phenylpropenal and subsequent cycloaddition of benzylamine. The imidazole intermediate was converted into 1‐benzyl‐5‐(chloromethyl)‐imidazolium chloride which was coupled to a glycine moiety via an enantioselective coupling with the bislactim ether of cyclo‐D‐valylglycine. Deprotection of the coupling product afforded L‐histidine in high optical purity. Syntheses for the isotopically labelled synthons were developed starting from simple, commercially available, highly enriched compounds. The labelled L‐histidines were characterized by mass spectrometry and 1H‐, 13C‐ and 15N‐NMR spectroscopy.
A new model for coenzyme B12 based on a Costa‐type ligand
Authors: Altink R. , 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

AbstractThe synthesis of a new Costa‐type ligand (H2mdo), in which the propylene bridge has been replaced by a methylenedioxy bridge has been accomplished: two molecules of butanedione monoxime are coupled via a CH2 group by reaction with CH2Cl2 and 50% aqueous NaOH in the presence of a phase‐transfer reagent. Dihalidocobalt and alkyl(halido)cobalt complexes of the deprotonated ligand have been prepared and structurally characterized by NMR spectroscopy.
Efficient route to highly functionalized tetrahydrofurans by stereocontrolled silicon‐directed cyclization
Authors: van Delft F. L. , van der Marel G. A. , van Boom J. H. 
Published: September 2010

AbstractCyclization of 3,4,6‐tri‐O‐benzyl‐2,5‐di‐O‐trimethylsilyl‐1‐deoxy‐1‐phenyldiisopropylsilyl‐L‐glucitol in the presence of BF3·Et2O or catalytic H2SO4 proceeds stereoselectively to give predominantly the fully benzylated 2,5‐anhydro‐L‐glucitol derivative without occurrence of the Peterson elimination.
Nucleophilic substitutions using O‐alkyl‐N,N′‐dialkylisoureas. Applications to ephedrines
Authors: Poelert Martin A. , Kellogg Richard M. , Hulshof L. A. 
Published: September 2010

AbstractDialkylcarbodiimides in the presence of a Cu1 catalyst react cleanly with the hydroxyl group of N‐methylated (1R,2S)‐ephedrine and (1S,2S)‐pseudoephedrine. These adducts react with nucleophiles like alkyl and aryl thiols as well as thioic acids and phthalimide to form the substitution products with overall retention of configuration. It is postulated that intramolecular participation of the amino group via an SN2 reaction leads to aziridium salts, which are subsequently opened by the nucleophiles via a second SN2 reaction. This synthetic approach is also useful for the inversion of simple secondary alcohols; on treatment with dicyclohexylcarbodiimide followed by benzothioic acid and treatment with LiAlH4, menthol was converted in good yield to neomenthane thiol.
Selective hydrogenation of acetic acid towards acetaldehyde
Authors: Pestman R. , Koster R.M. , Ponec V. 
Published: September 2010

AbstractAs a model reaction for the selective hydrogenation of carboxylic acids towards aldehydes, the reaction of acetic acid towards acetaldehyde has been investigated. Various oxides are used as catalysts, including platinum‐enriched oxides. It appeared that oxides with a moderate metal‐oxygen bond strength are good catalysts, provided that a source of activated hydrogen is present. On exposure to molecular hydrogen zero‐valent metals can produce activated hydrogen. Addition of precious metals, such as Pt, or completely reducing part of the oxidic catalyst can provide the zero‐valent metal. The hydrogenation probably occurs on the oxidic surface by a Mars and Van Krevelen type of mechanism.