bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthesis of 6H‐1,2‐oxazines by hetero Diels‐Alder reactions of nitroso alkenes towards methoxyallenes
Authors: Zimmer Reinhold , Reißig Hans‐Ulrich 
Published: July 2007

AbstractRegioselective hetero Diels‐Alder reactions of in‐situ generated nitroso alkenes 2–4 with methoxyallene derivatives 1 provide 4H‐1,2‐oxazines 5–7 with an exo‐methylene group at C‐5. These primary cycloadducts are smoothly transformed into conjugated 6H‐1,2‐oxazines 11–13 by base or acid catalysis. The bicylic nitroso alkene 17 and methoxyallene (1a) combine to give the tricyclic 1,2‐oxazine 18, thus demonstrating that an exo‐transition state is favoured in this [4+2] cycloaddition. The reaction of the sterically hindered methoxyallene 1h with nitrosostyrene affords the cycloadduct 22 in low yield. 22 is very likely formed by a two‐step Diels‐Alder reaction via a zwitterion. Allene derivatives lacking a methoxy group are not sufficiently reactive towards nitroso alkenes and do not provide 1,2‐oxazines.
Investigations on different coupling reagents for the synthesis of a cyclopeptide analog of neuropeptide Y
Authors: Hoffmann Eike , Beck‐Sickinger Annette G. , Jung Günther 
Published: July 2007

AbstractThe short‐cut analog of neuropeptide Y (NPY), NPY 1YESK‐Ahx‐25RHYINKITRQRY‐NH2, was synthesized on the amide anchor 5‐(4‐aminomethyl‐3,5‐dimethoxyphenoxy)valeric acid (ADPV) attached to polystyrene/1% divinylbenzene by using the 9‐fluorenylmethoxycarbonyl/tert‐butyl (Fmoc/tBu) strategy. Side‐chain‐to‐side‐chain cyclization of residues Glu2 to Lys30 of this linear heptadecapeptide amide was carried out by using different activating reagents under high‐dilution conditions of the free peptide. The use of diphenylphosphoryl azide (DPPA) with the addition of triethylamine gave the highest yield of cyclic peptide. Replacing the tertiary amine by dipotassium hydrogen phosphate as an insoluble inorganic base did not improve the cyclization. Complete cyclization was achieved within four hours by using 2‐(1H‐benzotriazol‐1‐yl) ‐1,1,3,3‐tetramethyluronium tetrafluoroborate (TBTU) in combination with 1‐hydroxybenzotriazol (HOBt) as activating agent, but the separation from excess TBTU resulted in lower yields. Reactions were monitored by HPLC and kinetic investigations were made. The identity and purity of the final product magnified image were proven by various analytical methods including atmospheric pressure ionization mass spectrometry (API‐MS). The receptor binding constant of the cyclic analog was found to be comparable to that of NPY.
Synthesis and circular dichroism of steroids with a 1,4‐benzodioxane chromophore: On the absolute configuration of (−)‐silandrin
Authors: Antus Sándor , Baitz‐Gács Eszter , Snatzke Günther , Tóth Tamás S. 
Published: July 2007

AbstractStarting from cholesterol the three possible stereoisomeric 1,4‐benzodioxanes 24, 31, 32 and a series of analogues with 2βH,3βH configuration (25–27, 29, 30) have been synthesized. The α band of the 1,4‐benzodioxane chrompohore has been unequivocally identified in the CD spectra between 325–300 nm. For its Cotton effect the same helicity rule is valid as for homochirally analogous tetralins: the P/M helicity of the heteroring leads to a positive/negative CD within the α‐band. The (2′R,3′R) configuration of 6 has been established by a comparison of its CD data with those of 39 and with the help of the above‐mentioned helicity rule. This allows the assignement of the (2S,2′R,3′R) configuration of (−)‐silandrin (3).
Synthesis and spectroscopic characterization of 15N‐labeled hexaaminobenzene derivatives
Authors: Wolff J. Jens , Limbach Hans‐Heinrich 
Published: July 2007

AbstractEfficient syntheses of [15N6]‐labeled hexaaminobenzene (6), hexakis(dimethylamino)benzene (7) and 2,2′,2″‐trimethylbenzotris(imidazol) (1) are described. The compounds are characterized by 15N CPMAS NMR spectroscopy.
Substituent effects in the 1,3‐dipolar cycloaddition reactions of 2‐methylenecephalosporins with diazoalkanes
Authors: Pitlik János , Csaba Jászberényi J. , Komáromi István 
Published: July 2007

AbstractThe 2‐methylenecephalosporins 1 undergo stereoselective 1,3‐dipolar cycloaddition reactions with diazoalkanes to give exclusively the spirocyclopropylcephalosporins 3. Substituens at C‐3, C‐4 and C‐7 of the cephalosporin nucleus do not display a significant effect on the reactivity of the 2‐exo double bond. However, reduction of the sulfoxides to sulfides has an inactivating influence. Reactions with substituted diazoalkanes proceed more slowly in every case. The results are explained by theoretical (PM3, AM1 and MNDO) calculations.
Biologically active glycosides from asteroidea, XXVIII. Glycosphingolipids from the starfish Asterias amurensis versicolor Sladen, 1. Isolation and structure of six new cerebrosides, asteriacerebrosides AF, and two known cerebrosides, astrocerebroside A and acanthacerebroside C
Authors: Higuchi Ryuichi , Jhou Jian Xin , Inukai Kazuyoshi , Komori Tetsuya 
Published: July 2007

AbstractSix new cerebrosides, asteriacerebroside A (1), B (2), C (3), D (4), E (7) and F (8), have been isolated from the two cerebroside molecular species obtained from the less polar fraction of the chloroform/methanol extract of the starfish Asterias amurensis versicolor Sladen. The structures of these cerebrosides have been determined on the basis of chemical and spectroscopic evidences. Two known cerebrosides, astrocerebroside A (5) and acanthacerebroside C (6), have also been isolated and characterized. Reversed‐ and normal‐phase HPLC were effective in isolating these cerebrosides, showing the very close similarity in their structures. Mass spectrometry of dimethyl disulfide derivatives of the cerebrosides was useful for the determination of the double‐bond position in the cerebrosides.
Functionally substituted vinyl carbanions, 44. Synthesis of odd‐numbered 13‐crown‐4 derivatives possessing a functional group and their application in C‐lithiation of acrylates
Authors: Jatzke Harald , Schmidt Richard R. 
Published: July 2007

AbstractThe synthesis of symmetrically hydroxy‐substituted 13‐crown‐ 4 derivatives 2 and 3 is reported. To this end, diol 7 is first deprotonated with potassium tert‐butoxide and then treated with ditosylate 6 in the presence of lithium perchlorate as a template. Base‐catalyzed addition of 2 and 3 to methyl propiolate affords β‐alkoxy‐substituted acrylates 1a and 1b, respectively. Treatment of 1a with LDA in THF generates the β‐C‐lithiated species 1a‐A as indicated by quenching with CH3OD and reaction with propanal; thus, β‐deutero derivative 1a‐(β‐D) and tetronate 4a, respectively, are obtained. Competition experiments between 1a and methyl β‐methoxyacrylate (1c) with LDA in THF exhibit for 1a a higher thermodynamic but practically the same kinetic acidity.
Synthese chiraler Bausteine aus D‐glucosamin‐hydrochlorid
Authors: Giannis Athanassios , Henk Thomas 
Published: July 2007

Synthesis of Chiral Building Blocks from D‐Glucosamine HydrochlorideWittig‐reaction of 2‐acetamido‐2‐deoxy‐D‐glucose (1) with the semistabilized ylide Ph3PCHPh yielded the epimeric chain‐elongated derivatives 2 and 3 in different amounts depending on the reaction conditions. Reaction of 2‐(tert‐butoxycarbonylamino)‐2‐deoxy‐D‐glucose (5) with Ph3PCHPh yielded the compound 8, or after intramolecular cyclisation, the derivatives 6 or 7. Compound 3 was transformed in three steps into the amino alcohol 10. The 3‐amino‐1,2‐diol derivative 17 and also the N,O‐protected α‐hydroxy‐β‐amino acid derivative 16 were obtained from 7. The N‐protected homophenylalanine derivatives 12 and 14 were available in two steps from 2 or 8.
Synthesis of 4‐nitro‐2H‐isoindole derivatives
Authors: Wojciechowski Krzysztof 
Published: July 2007

AbstractOxidation of nitro derivatives of 3,4‐dihydro‐1H‐2,3‐benzothiazine 2,2‐dioxides 1a–e in the presence of a base leads to nitro‐2H‐isoindole derivatives, 3a–e.
Natural product chemistry, 145. Synthesis of rac‐acridone‐coumarin dimers (acrimarins)
Authors: Reisch Johannes , Herath H. M. T. Bandara , Kumar N. Savitri 
Published: July 2007

AbstractThree new rac‐acridone‐coumarin dimers (acrimarins) 5, 6 and 7 have been obtained by condensation of (E)‐suberenol (1) with the corresponding acridones 2, 3 and 4.
Reactions of lithium salts of O‐alkyl oximes with halogens: A highly stereoselective oxidative coupling of 5,6‐dihydro‐3‐methyl‐4H‐1,2‐oxazine
Authors: Shatzmiller Shimon , Lidor Ramy , Bahar Eliezer , Goldberg Israel 
Published: July 2007

AbstractLithiation of 5,6‐dihydro‐3‐methyl‐4H‐1,2‐oxazine (4) in an unpolar solvent system (hexane/THF) at −65°C followed by reaction with Cl2,Br2, or I2 affords cleanly and stereoselectively 6 (RS,RS) of which an X‐ray structure analysis is described. In contrast, attempts to couple the halogenated 1,2‐oxazine derivative 5c have given, under various reaction conditions, equal amouts of 6 and 8 (meso). A mechanism of this reaction is discussed.
Reactions of 4‐(dicyanomethylene)‐3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one towards active methylene compounds
Authors: Metwally Saoud A. M. , El‐Naggar Galal M. , El‐Emary Talaat I. 
Published: July 2007

AbstractThe reaction of some active methylene compounds with 4‐(dicyanomethylene)‐3‐methyl‐1‐phenyl‐2‐pyrazoline‐5‐one (1a) has been investigated. This reaction involves a Michael addition to afford 4‐spirocyclobutenes 3 or cyclopyran‐2‐pyrazoline‐5‐ones 4, depending on the active methylene derivatives used. A possible rationalization of the reaction pathway is proposed.
Synthese von 6‐Methoxy‐2,5‐dimethyl‐2H‐isoindol‐4,7‐dion, einem Alkaloid aus Reniera‐Arten
Authors: Schubert‐Zsilavecz Manfred , Schramm Hans Wolfgang 
Published: July 2007

Synthesis of 6‐Methoxy‐2,5‐dimethyl‐2H‐isoindole‐4,7‐dione, an Alkaloid from Reniera Species6‐Methoxy‐2,5‐dimethyl‐2H‐isoindole‐4,7‐dione (4) can easily be obtained in high yields in a one‐pot synthesis by heating sarcosine (2) and paraformaldehyde in the presence of 3‐methoxy‐2‐methyl‐1,4‐benzoquinone (1).
Concave reagents, 9 Alcoholysis of diphenylketene catalyzed by concave pyridines and open‐chain analogs
Authors: Lüning Ulrich , Baumstark Roland , Schyja Wolfgang 
Published: July 2007

AbstractPseudo‐first‐order rate constants k(obs) for the (concave) pyridine‐catalyzed addition of ethanol to diphenylketene have been determined photometrically. The catalytic activity of the concave pyridines 1 or 2 is determined by their basicity and by their size. This effects a difference in k(obs) of up to three orders of magnitude. The decrease in catalytic activity by the concave shielding can be overcome by introduction of basicity‐increasing substituents into the pyridine ring (i.e. 1q). An amine–alcohol complex is probably the reactive species in this catalysis as the slope β of 0.3‐0.5 in a Brønsted plot supports.
Synthese von cis‐konfigurierten Bis(trifluormethyl)pyrethroiden
Authors: Rothermel Reinfried , Hanack Michael 
Published: July 2007

Synthesis of cis‐Configurated Bis(trifluoromethyl)pyrethroidstrans‐2,2‐Bis(trifluoromethyl)cyclopropanecarboxylates 2a, b are converted into the cis‐diastereomers by base‐catalyzed epimerization via the bicyclic lactones 3a, b. Dehydration of cis‐2a and cleavage of the ester function leads to the fluorinated chrysanthemic acid 4b, which is converted into the pyrethroids 4d, e. cis‐2b is oxidized by pyridinium chlorochromate to give methyl cis‐3‐formyl‐2‐2‐bis(trifluoromethyl)‐cyclopropanecarboxylate (hexafluorocaronaldehydic acid methyl ester) (5). This compound, which is very sensitive to isomerization, is converted into the pyrethroid esters 6a, b predominately retaining the cis configuration; however, by introducing the 2,2‐dichlorovinyl side chain the trans diastereomer is obtained. The starting materials trans‐2a, b are prepared by the reaction of aldehydes 9a, b with 2,2‐dichlorohexafluoropropane and triphenylphosphine followed by cyclopropanization of the resulting 1,1‐bis(trifluoromethyl)olefins 10a, b with (ethoxycarbonylmethylene)dimethylsulfurane (14).
New stereoisomers of quinic acid and their lactones
Authors: Scholz‐Böttcher Barbara M. , Ernst Ludger , Maier Hans Gerhard 
Published: July 2007

AbstractHeating of (−)‐quinic acid [(−)‐1] at reflux temperature with 90% acetic acid/concd. H2SO4 (67/1) yields a mixture of six stereoisomeric quinic acids (four meso forms and two pairs of enantiomers), four γ‐quinides (four pairs of enantiomers), and three δ‐quinides (two meso forms and one enantiomeric pair). The 1H‐ and 13C‐NMR spectra for most of these compounds are given. The fully trimethylsilylated derivatives of all the compounds are characterized by high‐resolution GC/MS. The existence of neo‐quinic acid (6), its γ‐ (10) and δ‐lactone (12), of epi‐δ‐quinide (13), of two meso‐quinic acids, and of another γ‐quinide is reported for the first time. The structures and configurations of neo‐quinic acid, neo‐γ‐, neo‐δ‐, and epi‐δ‐ quinide are derived from their NMR spectra. All stereoisomeric quinic acids and their γ‐and δ‐lactones are also formed under the roasting conditions of coffee.
2,2′‐Binaphthyliden‐1,1′ ‐dione – Farbe und Struktur
Authors: Göltner Christine , Laatsch Hartmut 
Published: July 2007

2,2′‐Binaphthylidene‐1,1′ ‐diones – Colour and StructureThe UV spectra of deep purple to green 2,2′‐binaphthylen‐1,1′‐diones 3 may be explained by substituent increments with high reliability. This allows assistence in structure elucidation of substituted 1‐naphtholes 1a by UV/Vis measurements of their oxidation products, or colour adjustment of 3 for use in diagnostic purposes. Also highly soluble derivatives of 3 were synthesized for the first time.
Synthesis of Shikonin and Alkannin
Authors: Braun Manfred , Bauer Claus 
Published: July 2007

AbstractThe enantiomeric naturally occurring naphthoquinones shikonin [(R)‐1] and alkannin [(S)‐1] have been synthesized in a thirteen‐step procedure in 44 to 65% e.e. The stereogenic centers of (R)‐1 and (S) are created by the reaction of naphthaldehyde 3 with (R)‐ and (S)‐2‐hydroxy‐1,2,2‐triphenylethyl acetate (2), respectively. In order to find out a rationalization for the unexpectedly low diastereoselectivity in this aldol addition, a series of substituted aromatic aldehydes 12a–h has been treated with (R)‐2.
Metallkomplexe mit Tetrapyrrol‐Liganden, LX. Pseudo‐Sandwichkomplexe: Komplexe drei‐ und vierwertiger Metall‐Ionen mit Porphyrin‐ und Schiff‐Base‐Liganden
Authors: Buchler Johan N. W. , Hammerschmitt Peter 
Published: July 2007

Metal Complexes with Tetrapyrrole Ligands, LX. – Pseudo Sandwich Complexes: Complexes of Metal(III) and ‐(IV) Ions with Porphyrin and Schiff‐Base LigandsThe synthesis of novel metal complexes with a porphyrinate, (P)2–2), and an ethylenebis(salicylidenealdiminate) or similar tetradentate open chelate, (L‐4)2−, as ligands is described. Their general formula [M(P)(L‐4)]n is realized with n = o and M = ZrIV or HfIV or n = −1 with M = YIII or TbIII; in the latter, an additional Li+ ion warrants electroneutrality. These complexes are prepared from the metal monoporphyrinates MIV(P)X2 or MIII(P)X (X = acetylacetonate) and the corresponding Schiff‐base derivatives, H2(L‐4) or Li2(L‐4), respectively. 1H‐NMR data prove the square antiprismatic configuration of the ZrIV species at 295 K which is abandoned at 373 K when the (P)2− and (L‐4)2− freely rotate about each other. Electrochemical measurements show that oxidations and reductions involve only the porphyrin ligands. The redox potentials experience shifts that can be understood in terms of the Hammett parameters σ of the substituents at (L‐4)2−.
Untersuchung des stereochemischen Einflusses von Substituenten in 3‐Stellung an Cholsäurederivaten mit Hilfe von 1D‐ und 2D‐NMR‐Methoden
Authors: Wollborn Ute , Leibfritz Dieter 
Published: July 2007

1D‐ and 2D‐NMR Studies on the Stereochemical Influence of C‐3 Substituents in Derivatives of Cholic Acid1)The structural effects of C‐3 sustituents on two derivates of cholic acid have been studied by 1D‐as well as homonuclear and heteronuclear 2D‐NMR spectra. The stereochemical structure of ring A is derived from homonuclear vicinal coupling constants. The consequences of C‐3 substitution on 1H and 13C chemical shifts, on stereochemical and electronical effects are discussed.
Synthesis of oxime‐based macrocyclic systems by oxidative coupling of an aza‐allyl anion derivative – cyclooligomerization of dioxime diethers
Authors: Shatzmiller Shimon , Menashe Naim , Shalom Eytan , Bahar Eliezer 
Published: July 2007

AbstractReaction of the dilithium salts of the dioxime diethers 1 gives the polyoxime‐based macrocyclic systems 2–4. Temperature and lithium effects indicate that mixed aggregates play an important role in the formation of these heterocyclic systems by oxidative coupling. An X‐ray structure analysis of 3f has been carried out showing that the thermodynamically unfavored Z configuration is a characteristic feature of this reaction product.
Efficient and diastereoselective synthesis of (+)‐ and (−)‐grandisol and 2‐[(1R,2S)‐2‐isopropenylcyclobutyl]ethanol (demethylgrandisol) in high purity
Authors: Hoffmann Norbert , Scharf Hans‐Dieter 
Published: July 2007

AbstractAcetone‐sensitized [2 + 2] photocycloaddition of ethylene to chiral butenolides 3 and 15 yields diastereomeric cyclobutanes, which are transformed to (+)‐(1) and (−)‐grandisol (ent‐1) (overall yield 34–36%) and to 2‐[(1R,2S)‐2‐isopropenylcyclobutyl]ethanol (demethylgrandisol) (2) (overall yield 25%) in five steps.
Oxime von Derivaten der 2‐Acetamido‐2,4‐didesoxy‐D‐xylo‐hexose und der entsprechenden Uronsäure
Authors: Györgydeák Zoltán 
Published: July 2007

Oxime Derivatives of 2‐Acetamido‐2,4‐dideoxy‐D‐xylo‐hexose and of the Corresponding Uronic AcidOximes and O‐methyl oximes of 3‐O‐protected 2‐acetamido‐2,4‐dideoxy‐D‐xylo‐hexose and of methyl 2‐acetamido‐2,4‐dideoxy‐D‐xylo‐hexuronate (14, 15, 16, 18, 19 and 26) have been prepared from 2‐acetamido‐2‐deoxy‐D‐glucopyranose. Their structures have been elucidated by 1H‐ and 13C‐NMR data.
Enzymes in Organic Synthesis, 8. Synthesis of enantiomerically pure prostaglandin intermediates by enzymatic transesterification of (1S*,5R*,6R*,7R*)‐(±)‐7‐hydroxy‐6‐hydroxymethyl‐2‐oxabicyclo[3.3.0]octan‐3‐one
Authors: Weidner Judith , Theil Fritz , Kunath Annamarie , Schick Hans 
Published: July 2007

AbstractLipase Amano PS is a suitable biocatalyst for the highly regio‐ and enantioselective transesterification of the racemic prostaglandin building block (1S*,5R*,6R*,7R*)‐(±)‐7‐hydroxy‐6‐hydroxymethyl‐2‐oxabicyclo[3.3.0]octan‐3‐one (rac‐1) yielding (1S,5R,6R,7R)‐(−)‐6‐acetoxymethyl‐7‐hydroxy‐2‐oxabicyclo[3.3.0]octan‐3‐one (2) and the unreacted (1R,5S,6S,7S)‐(+)‐enantiomer ent‐1.
Diels‐Alder reactions of 2,3‐dimethylenecephalosporins
Authors: Gunda Tamas E. , Kövér Katalin E. 
Published: July 2007

Abstract2,3‐Dimethylenecephalosporin esters 1 undergo Diels‐Alder reaction with ethyl methacrylate and O‐ethyl S‐methyl dithiooxalate. The structure of the former reaction product 3a is in accordance with 1H‐NMR data as well as with theoretical considerations (FMO, MMX)
Conversion of (−)‐α‐narcotine into (+)‐papaveroxinoline and (+)‐macrantaline
Authors: Rozwadowska Maria D. , Banaszyński Slawomir 
Published: July 2007

Abstract(−)‐α‐Narcotine (5), a phthalideisoquinoline alkaloid, is converted into two secoberbines: (+)‐papaveroxinoline (3) and (+)‐macrantaline (1). The reaction sequence involves reduction of 5 to the diol 6 followed by selective monoacetylation to (+)‐3. Hydrogenolysis of the latter affords (+)‐1.
Synthesis of 3,5‐dichloro‐6‐ethyl‐2,4‐dihydroxybenzoic acid – the aromatic constituent of lipiarmycin A3
Authors: Alexy Markus , Scharf Hans‐Dieter 
Published: July 2007

Abstract3,5‐Dichloro‐6‐ethyl‐2,4‐dihydroxybenzoic acid (5, homodichloroorsellinic acid) is the polysubstituted aromatic carboxylic acid found in the macrolide antibiotic lipiarmycin A3. A convenient synthesis of the title compound from ethyl 2‐pentenoate and ethyl acetoacetate is described (five steps, 41% overall yield).
Solution structure of phalloidin obtained by NMR spectroscopy in [D6]DMSO and molecular dynamics calculation in vacuo and in water
Authors: Kessler Horst , Wein Thomas 
Published: July 2007

AbstractHomo‐ and heteronuclear NMR techniques have been used to assign all proton and most of the carbon resonances of phalloidin (1) [cyclic(L‐alanyl‐D‐threonyl‐L‐cysteinyl‐cis‐4‐hydroxy‐L‐prolyl‐L‐alanyl‐L‐mercapto‐L‐tryptophyl‐4,5‐dihydroxy‐L‐leucyl) cyclic (3→6) sulfide], a toxic bicyclic heptapeptide of the poisonous mushroom Amanita phalloides. Intramolecular proton–proton distances derived from rotating‐frame NOE experiments have been used as constraints in energy minimization and molecular dynamics calculations using GROMOS. Charge reduction of solvent‐exposed NH protons has been used to minimize artifacts in the in vacuo calculation. The structure has been proven to be unstable without constraints in vacuo. Hence, a procedure is proposed in which first restrained MD in vacuo is performed and refinement is carried out by restrained or unrestrained MD in water.
Synthese von 5,15‐diarylsubstituierten Porphyrinen über Aminomethylierung von Bis(4‐ethyl‐3‐methyl‐2‐pyrryl)phenylmethanen
Authors: Hombrecher Hermann K. , Horter Gaby 
Published: July 2007

Synthesis of 5,15‐Diaryl‐Substituted Porphyrins by Aminomethylation of Bis(4‐ethyl‐3‐methyl‐2‐pyrryl)phenylmethanesThe synthesis of unsymmetrically diarylsubstituted porphyrins 11a‐g (yields 5–19%) is described. Aminomethylation of dipyrromethane 6a with Mannich reagent 9 in acetonitrile leads to the intermediate 10, which is directly converted into the porphyrins 11 by acid‐catalysed coupling with the dipyrromethanes 6.
Zur Reaktion von Dialkylphosphiten mit α‐Enonen, II. 2:1‐Addukte aus Dimethylphosphit und α‐Enonen: Darstellung von (1‐Hydroxy‐1,3‐alkandiyl)diphosphonaten und 5‐Dimethoxyphosphoryl‐2‐methoxy‐1,2‐oxaphospholan‐P‐oxiden
Authors: Öhler Elisabeth , Zbiral Erich 
Published: July 2007

Reaction of Dialkyl Phosphites with α‐Enones, II. – 2:1 Adducts from Dimethyl Phosphite and α‐Enones: Synthesis of (1‐Hydroxy‐1,3‐alkanediyl)diphosphonates and 5‐Dimethoxyphosphoryl‐2‐methoxy‐1,2‐oxaphospholane P‐OxidesOn NaOCH3‐catalyzed reaction with two equivalents of dimethyl phosphite (2), various α‐enones 1 are transformed into the diphosphonates 5 (e.g. 5a, 5b, 5e, 5f), which, depending on the structure of the enone, can further react with ring closure to give the 1,2‐oxaphospholanes 6 (e.g. 6c, 6g, 6h), or with phosphonate‐phosphate rearrangement of the α‐hydroxyphosphonate moiety to yield compounds 7 (e.g. 7d). The formation of the 2:1 adducts is believed to occur via addition of 2 to the carbonyl group of the (3‐oxoalkyl)phosphonates 4, formed from thermodynamically controlled 1,4 addition of 2 to 1. Compounds 4 could also be treated with 2 to yield 2:1 adducts (e.g. 4c → 5c, 4d → 5d, 4d → 7d).
Improved synthesis of α‐L‐Fuc(1→4)‐β‐D‐GlcNAc and α‐L‐Fuc(1→6)‐β‐D‐GlcNAc building blocks: A convergent strategy employing 4‐O→6‐O acetyl migration; NOE data of the protected α‐1,4‐linked disaccharide
Authors: Peters Thomas , Weimar Thomas 
Published: July 2007

AbstractThe synthesis of the two ethylthio disaccharide building blocks 10 and 17 was achieved by coupling of fucosyl bromide 9 with the acceptor alcohols 6 and 7 under in situ anomerization conditions. The selectively protected 2‐deoxy‐2‐phthal‐imidoglucose derivative 7 was derived from 6 by utilizing an optimized acetyl migration reaction. The ethylthio function in disaccharides 10 and 17 was activated with bromine, and excess bromine was removed with cyclohexene. The sensitive 1,6‐linkage in the disaccharide 10 proved to be stable under these activating conditions. The disaccharide bromides 11 and 18 were treated with methanol to afford after deblocking the methyl glycosides 16 and 23. Homonuclear 1H‐NOE data were obtained for the protected 1,4‐linked disaccharide 17 suggesting that its preferred solution conformation is rather similar to the solution conformation of the deblocked disaccharide 23 in aqueous solution as known from literature data.