bluuebunny/crossref_metadata_2025_split huggingface dataset:
Synthese und Charakterisierung von β‐phosphoranalogen Asparaginsäure‐Derivaten: 2‐Amino‐3‐aryl‐3‐phosphorylpropionsäure‐Derivate
Authors: Preußler Carola , Schnepp Kathrin , Kellner Kurt 
Published: July 2007

Synthesis and Characterization of β‐Phosphorus Analogues of Aspartic Acid Derivatives: 2‐Amino‐3‐aryl‐3‐phosphorylpropionic Acid DerivativesThe 4‐benzylidene‐4,5‐dihydro‐5‐oxazolones 1 react with alkali dialkyl phosphites 2 to give the alkali salts of 4‐[(dialkoxyphosphoryl)methyl]‐5‐hydroxyoxazoles 3. Silylation of 3 with ClSiMe3 yields the 5‐siloxyoxazole derivatives 4. Treatment of 4 with alcohols or water provides 3‐aryl‐2‐(benzoylamino)‐3‐(dialkoxyphosphoryl)propionic acid esters 6 and propionic acids 7, respectively. The ratio of the diastereomeres of 6 (A, B) and 7 (A, B) depends on the reaction conditions. A remarkable different diasteroselectivity is observed in basic versus acidic media. The proposed reaction pathway is supported by characterization of the intermediate 4‐[(dialkoxyphosphoryl)methyl]‐4,5‐dihydro‐5‐oxazolone 8. A complete hydrolysis of compounds 6 produces the 3‐phosphonoaspartic acid 9.
Polymorphie an chiralen phosphoranalogen Asparaginsäure‐Derivaten: Kristall‐ und Molekülstruktur von 2‐(Benzoylamino)‐3‐(diethoxyphosphoryl)‐3‐(4‐methoxyphenyl)propionsäure‐methylester
Authors: Preußler Carola , Kellner Kurt , Sieler Joachim 
Published: July 2007

Polymorphy on Chiral Phosphorus Analogues of Aspartic Acid Derivatives: Crystal and Molecular Structure of Methyl 2‐(Benzoylamino)‐3‐(diethoxyphosphoryl)‐3‐(4‐methoxyphenyl)propionateThe diastereomers of the title compound 1 were characterized by X‐ray structure analyses. The relative configuration of diastereomer A is determined as RS/SR, diastereomer B shows RR/SS configuration. Depending on the different configurations hydrogen bonds are formed by the phosphoryl oxygen with the amide hydrogen intermolecularly (form A) or intramolecularly (B). No interaction is observed of the carboxylate and the amide oxygen, respectively, with the amide hydrogen.
Endogenous alkaloids in man, IX. Potential tryptophan‐derived alkaloids in chloral‐treated patients: Synthesis and stereostructure
Authors: Bringmann Gerhard , Hille Annette , Stäblein Michaela , Peters Karl , Von Schnering Hans Georg 
Published: July 2007

AbstractThe trichlorotetrahydroharmancarboxylic acids 5a and 5b were shown to be formed in aqueous medium under neutral, physiological conditions from the amino acid tryptophan and the nonnatural aldehyde chloral. Preparative diastereomer resolution and configurational analysis were performed via the methyl esters 7a/7b. The structure of 7b was proved by an X‐ray structural analysis. By cautious hydrolysis, the chloral‐derived potential „mammalian alkaloids”︁ 5a and 5b were obtained in analytically pure form.
Stereoselective synthesis of alcohols, XL. Stereoselective cyclization of 7‐oxo‐2‐heptenylboronates
Authors: Hoffmann Reinhard W. , Niel Gilles 
Published: July 2007

AbstractIntramolecular allylboration reaction of 7‐oxo‐2‐heptenyl boronates leads to 2‐vinylcyclopentanols. The cyclization proceeds in a stereospecific manner, such that the (E)‐allylboronate 8 is converted into trans‐2‐vinylcyclopentanol (2) and the (Z)‐allylboronate 10 into cis‐2‐vinylcyclopentanol (3). Asymmetric induction originating from stereogenic centers placed between the boronate and the aldehyde function has been found to be low.
Stereoselective synthesis of alcohols, XLI. Chirality transfer to generate quaternary stereogenic centers by an allylboration reaction
Authors: Hoffmann Reinhard W. , Schlapbach Achim 
Published: July 2007

AbstractThe acyclic alcohols 13 and 14 having a neighboring quaternary stereogenic center can be obtained in diastereoselectivities of > 95% by addition of the ß,γ,γ‐trisubstituted allylboronates 12 to aldehydes. Starting from the nonracemic allylboronates 19 of presumed 84–92% e.e., we have obtained the alcohols 13a and 14a with the corresponding levels of the e.e.
Asymmetric Syntheses via Heterocyclic Intermediates, XLV. Asymmetric Synthesis of Diastereomerically and Enantiomerically Pure 3‐Substituted (2R,3S)‐serine Methyl Esters
Authors: Beulshausen Tessa , Groth Ulrich , Schöllkopf Ulrich 
Published: July 2007

AbstractThe titanium derivative 2 of the bislactim ether 1 of cyclo(‐L‐Val‐Gly‐) reacts with aldehydes and ketones 3 highly diastereoselectively to give the syn‐addition products 4. Upon hydrolysis with diluted trifluoroacetic acid the compounds 4 yield besides methyl L‐valinate the (2R,3S)‐threo‐serine methyl esters 5.
Heterocyclization with iminium chlorides, V. Condensation of 1,3‐dichlorotrimethinecyanines with 1,3‐ and 1,2‐dinucleophiles
Authors: Tóth Gábor , Kovács Attila , Bitter István , Duddeck Helmut 
Published: July 2007

AbstractCyclic 1,3‐dichlorotrimethinecyanines 1 were used for the preparation of condensed polycycles 2–13 with high regioselectivity. In the case of five‐membered cyanines the exclusive formation of the linear‐type products was observed, while with six‐ and seven‐membered cyanines the linear or angular type of products were obtained, depending on the character of the nucleophile. The structures of the products were supported by 1H‐, 13C‐ and 15N‐NMR data, NOE difference spectroscopy, and different two‐dimensional carbon‐proton correlation measurements.
Unexpected transformations of camphor (thio)semicarbazones under acetylating conditions
Authors: Somogyi László 
Published: July 2007

AbstractThe formation of camphor mono‐ and diacetylhydrazones (1, 4, 6) and a stereoselective synthesis of the spirothiadiazoline (1R)‐(+)‐2 is described. The degradation of (thio)semicarbazones 3 (X = O, S) and diacetylhydrazone 4 to the acetylhydrazone 6 has been performed.
Reactions of 3‐acyl‐substituted 2H‐1‐benzopyran‐2‐ones with acid anhydrides, II
Authors: Bojilova Anka , Rodios Nestor , Nicolova Rositsa , Ivanov Christo 
Published: July 2007

Abstract3‐Pivaloyl‐2H‐1‐benzopyran‐2‐one (6) reacts with acid anhydrides in the presence of triethylamine to give 4‐(2‐oxoalkyl)‐2‐oxochromans 7 and 3‐pivaloyl‐2‐oxochroman (8) in moderate yields. Also 3‐propionyl‐ and 3‐isobutyryl‐2H‐1‐benzopyran‐2‐ones (9) react with acid anhydrides under the same reaction conditions to give 4‐(2‐oxoalkyl)‐2‐oxochromans 10 and pyrano[3,4‐c][2H]chromenes 11 as the main products. A mechanistic explanation for the formation of these compounds is proposed.
Thermal Degradation of Glycosides, IV. Degradation of flavonoid glycosides
Authors: Kim Youn Chul , Higuchi Ryuichi , Kitamura Yoichi , Komori Tetsuya 
Published: July 2007

AbstractBy mere heating, the flavone (1, 7), flavanone (4, 10), and flavonol glycosides (13, 14) are converted into their aglycones and monoglycosides. The products of pyrolysis have been isolated by chromatography and their structures elucidated by chemical and spectroscopic methods. The compound derived from the sugar moiety in the pyrolysis of glucosides has been identified as levoglucosan (17). From the structures of some minor products (16, 18, 19), generated by the thermal degradation, a mechanism of their generation and the elucidation of the structures of rearranged ions (for example [M + 146 + H]+), often generated in the FD‐mass spectra of glycosides, are presented.
An improved synthesis of bicyclo[3.3.0]octane‐2,6‐dione
Authors: Quast Helmut , Janiak Rolf 
Published: July 2007

AbstractThe Michael addition of dimethyl malonate (12) to tert‐butyl acrylate (11), carried out without solvent, affords the triester 13a in 88% yield on a kg scale. Selective partial hydrolysis of 13a produces the monoacid 13b almost quantitatively. The Kolbe electrolysis of 13b furnishes the tetraester 7c as a crystalline 1:1 mixture of diastereomers in 62–74% yield. The Dieckmann condensation of 7c is induced by sodium hydride/tert‐butyl alcohol in tetrahydrofuran and yields the enolized β‐oxo ester 8c which, on acidic hydrolysis followed by decarboxylation, produces the title diketone 2 in 90% yield, based on 7c. Thus, the useful diketone 2 is obtained in 46–55% overall yield on a 100‐g scale.
Synthesis of Sphingosine Relatives, XI. Synthesis of wheat grain cerebroside with fruiting‐inducing effect on Schizophyllum commune
Authors: Mori Kenji , Kinsho Takeshi 
Published: July 2007

Abstract(2S,3R,8Z)‐1‐O‐(β‐D‐Glucopyranosyl)‐N‐hexadecanoyl‐8‐sphingenine (1) and its (8E) isomer 1(E) were synthesized by starting from D‐(−)‐tartaric acid.
Aminosäureester als chirale Hilfsgruppen bei Barbier‐Reaktionen in wäßriger Lösung
Authors: Waldmann Herbert 
Published: July 2007

Amino Acid Esters as Chiral Auxiliaries in Barbier‐Type Reactions in Aqueous SolutionValine and proline benzyl ester are converted into the aliphatic and aromatic α‐oxo amides 5 by activation of the respective α‐oxo acid by means of N,N′‐diisopropylcarbodiimide. The α‐oxo amides 5 undergo Barbier‐type reactions with differently substituted allyl halides in the presence of zinc and pyridinium toluenesulfonate in water/THF (2:1, v/v) at 4°C. Thereby, the α‐hydroxy amides 8/9 are formed in high yields and, in the case of the proline ester amides, with diastereomer ratios of 4–6:1. In the absence of any allyl halide, or if the addition of the allyl moiety to the carbonyl groups is only slow, the oxo groups are reduced to secondary alcohols, thus giving rise to the α‐hydroxy amides 12/13. During the reduction of the pyruvamide 5d also the competitive formation of the pinacol adduct 15 is observed. These results indicate that in the Barbier reactions in aqueous solution radicals are involved as intermediates.
Synthesis of the 4‐Pyridine Analog of Kostanecki's Triketone. Determination of Constitution and Stereochemistry by 2D‐NMR Spectroscopy and X‐ray Structural Analysis
Authors: Kessler Horst , Mronga Siggi , Kutscher Bernhard , Müller Arndt , Sheldrick William S. 
Published: July 2007

Abstract4‐Acetylpyridine reacts stereoselectively with benzaldehyde under basic conditions to afford rac‐1. The constitution of 1 was determined by the long‐range connectivities revealed by the H, C‐COLOC spectrum. The relative stereochemistry of the chiral centers C‐2 to C‐6 was obtained from 3JHH couplings. The stereochemistry at the non‐proton bearing C‐1 was established by through‐space connectivities from ROESY and semiquantitative analysis of 3JCH from an inverse 2D‐NMR spectrum (HMBC). The NMR findings were confirmed by single crystal X‐ray diffraction.
An expedient synthesis of rac‐2,3‐di‐O‐stearoyl‐1‐thiophosphatidylcholine via thiophosphatidic acid diesters
Authors: Młotkowska Barbara 
Published: July 2007

AbstractA convenient triester approach to rac‐2,3‐di‐O‐stearoyl‐1‐thiophosphatidylcholine (7) involving the preparation of S‐[2,3‐bis(stearoyloxy)propyl] O‐(2,4‐dichlorophenyl) O‐methyl thiophosphate (4) followed by demethylation, coupling of the resulting salt 5 with choline 2‐mesitylenesulfonate and subsequent removal of 2,4‐dichlorophenyl protecting group is described.
Hexafluoraceton als Schutzgruppen‐ und Aktivierungsreagenz in der Aminosäure‐ und Peptidchemie, 7. Synthese von γ‐Oxo‐α‐aminosäure‐Derivaten aus Asparaginsäure
Authors: Burger Klaus , Rudolph Martin , Neuhauser Horst 
Published: July 2007

Hexafluoroacetone as Protecting Group and Activation Reagent in Amino Acid and Peptide Chemistry, 7. – Synthesis of γ‐Oxo α‐Amino Acid Derivatives from Aspartic AcidOptically pure γ‐oxo α‐amino acids are obtained on reaction of acid chloride 2 with aromatic and heteroaromatic compounds under Friedel‐Crafts conditions.
Products from furans, 13. Synthesis of 6‐acyloxy and 6‐alkoxy derivatives of 2H‐pyran‐3(6H)‐ones
Authors: Constantinou‐Kokotou Violetta , Kokotos George , Georgiadis Minas P. 
Published: July 2007

AbstractThe 6‐hydroxy‐2H‐pyran‐3(6H)‐ones 1a–d are esterified stereoselectively with acetic and formic acid, and with several amino acids and peptide derivatives using the DCC/DMAP method. The direct synthesis of the 6‐alkoxy derivatives 3g–k is also studied.
Synthesis of α‐amino phosphonic acids via oxoiminium salts
Authors: Shatzmiller Shimon , Dolitzky Ben‐Zion , Meirovich Revital , Neidlein Richard , Weik Christian 
Published: July 2007

AbstractThe oxoiminium salts 4a, b, and 8 obtained by alkylation with Et3OBF4 of the aldonitrones 3a, b, and 7 react with diphenyl hydrogen phosphite to give the N‐alkoxy α‐amino phosphonic esters 6 and 9a, b. Similarly, the cyclic imine oxides 10a, b and the cyclic oxime ethers 14a, b afford the α‐branched N‐alkoxy α‐amino phosphonic esters 12a, b and 16a, b, respectively. Hydrogenolysis and ester hydrolysis affords the α‐methyl α‐amino phosphonic acid hydrochlorides 13a, b and 17a, b.
Synthesis of β‐lactosyl 1‐thioceramide
Authors: Bär Thomas , Schmidt Richard R. 
Published: July 2007

Abstract3‐O‐Benzoyl‐azidosphingosine 3 was transformed into the corresponding 1‐thio derivative 6. Its sodium sulfide salt 6A was treated with hepta‐O‐acetyl‐α‐lactosyl bromide 8 to provide after complete O‐deprotection the β‐connected thioglycoside 9. Azido group reduction and N‐palmitoylation led to the desired β‐lactosyl thioceramide 1; for structural assignments it was converted into the per‐O‐acetyl derivative 2.
Geometrically directed lithiation of O‐Alkyloximes for the synthesis of linear polyethers
Authors: Shatzmiller Shimon , Dolitzki Ben‐Zion 
Published: July 2007

AbstractFor synthetic purposes, the polyether‐based secondary alcohols 7 and 8 were prepared from acetone O‐methyloxime (1). This applies the (Z) effect for the geometry‐directed alkylation sequence, recovery of the keto group and reduction. In contrast to 11, α‐phenylthio‐substituted O‐alkyloxime 26 was found to be unsuitable as starting material for such synthesis. The strong effect of bivalent sulfur in the α‐position shadows the (Z) effect and permits only lithiation next to the sulfur atom.
Inter‐ and intramolecular hetero‐Diels‐Alder reactions, 37. Syntheses of the 3‐amino sugar glycosides rac‐4‐deoxydaunosaminide rac‐4‐deoxyristosaminide, and rac‐acosaminide
Authors: Tietze Lutz F. , Hartfiel Uwe , Hübsch Thomas , Voß Edgar , Bogdanowicz‐Szwed Krystyna , Wichmann Jürgen 
Published: July 2007

AbstractThe hetero‐Diels‐Alder reaction of the phenylthio‐activated N‐monoacyl‐ and N,N‐diacyl‐enamino ketones 8a‐c containing a methyl group at position 2 of the oxadiene with the electron‐rich dienophiles 9a‐c yields the exo/endo adducts 10a‐d and 11a‐d in 82–95% yield with the endo adducts as the main products. The enamino ketone 8d with a S‐ethyl group at C‐3 does not react. Hydrogenation of 11a with Raney nickel in THF leads to the desulfurized dihydropyran 12, whereas in MeOH gives stereoselectively the perhydrophthalimido derivative 13, which, after deprotection, yields the β‐methyl glycoside 14 of rac‐4‐deoxydaunosamine. Under similar conditions 10c is converted into the β‐ethyl glycoside 15 of rac‐N‐benzoyl‐4‐deoxyristosamine. Stereoselective hydroboration of 12 affords 17 and subsequent cleavage of the protecting group leads to the β‐methyl glycoside 18 of rac‐acosamine.
Diastereomeric 5,6‐dimethyl‐4H‐1,3‐dioxin‐4‐ones from (−)‐(1R,4S)‐menthone: Synthesis and NMR analysis
Authors: Jansen Ursula , Runsink Jan , Mattay Jochen 
Published: July 2007

AbstractThe two diastereomers of spirocyclic 5,6‐dimethyl‐4H‐1,3‐dioxin‐4‐one (5, 6) have been synthesized by acetalization of tert‐butyl 2‐methyl‐3‐oxobutanoate (2) with (−)‐menthone (4). Their structures have been determined by NMR analysis.
Pyrazino[2,3‐c]‐1,2,6‐thiadiazine 2,2‐dioxides. Synthesis of SO2 analogues of folic acid antagonists
Authors: Alkorta Ibon , Goya Pilar , Páez Juan Antonio , Pérez Concepción 
Published: July 2007

AbstractThe synthesis of novel analogues of foric acid (FA) antagonists derived from the pyrazino[2,3‐c]‐1,2,6‐thiadiazine 2,2‐dioxide system incorporating the glutamic acid side chain at the 7‐position is described. No significant DHFR inhibition of cytotoxic activity has been found with these compounds.
Synthese und Stereochemie von 4‐Thiazolidinylphosphonsäureestern
Authors: Martens Jürgen , Kintscher Jürgen , Lindner Karen , Pohl Siegfried , Saak Wolfgang , Haase Detlev 
Published: July 2007

Synthesis and Stereochemistry of Dimethyl 4‐ThiazolidinylphosphonatesDimethyl phosphite adds to the azomethine bond of 2,5‐dihydrothiazoles 1 to produce dimethyl 4‐thiazolidinylphosphonates 2. Depending on the reaction conditions diastereomeric mixtures 2 are formed and explained by a two‐step mechanism. Assignment of configurations is proved by an X‐ray structure analysis of the thermodynamically more stable stereoisomer of 2c. N‐Acylated derivatives 5 could not be obtained by direct acylation of 2 but by a TiCl4‐catalyzed Michaelis‐Arbusov‐type reaction of trimethyl phosphite with N‐acyl‐4‐methoxythiazolidines 3. Phosphonates 5 are formed with high diastereoselectivity.
Über Pyridinium‐N‐phenolat‐Betaine und ihre Verwendung zur Charakterisierung der Polarität von Lösungsmitteln, XVI. Bestimmung der empirischen Lösungsmittelpolaritäts‐Parameter ET(30) und AN für 55 substituierte Phenole
Authors: Spange Stefan , Lauterbach Manfred , Gyra Anett‐Kathrin , Reichardt Christian 
Published: July 2007

Pyridinium N‐Phenoxide Betaines and Their Application for the Characterization of Solvent Polarities, XVI1). – Determination of the Empirical Parameters of Solvent Polarity ET(30) and AN for 55 Substituted PhenolsBy means of the negatively solvatochromic dyes 1 and 2, the empirical solvent polarity parameters ET(30) and AN (Acceptor Number) are determined for solutions of 55 substituted phenols in 1,2‐dichloroethane as inert solvent (Table 1). The ET(30) values and Acceptor Numbers are compared with each other and with corresponding literature values, determined in neat substituted phenols (Table 2). The influence of the phenolic substituents on both solvent parameters is discussed with respect to their electronic and steric effects as well as to the self‐association of phenols in solution. Polyhydroxybenzenes such as resorcinol and pyrogallol exhibit both high solvent polarity and acceptor properties, whereas substituents in positions 2 and 6 of phenols decrease their polarity and acceptor strength.
Biologically active glycosides from asteroidea, XXVI. Stereochemistry of the four diastereomers of ceramide and ceramide lactoside
Authors: Sugiyama Shigeo , Honda Masanori , Higuchi Ryuichi , Komori Tetsuya 
Published: July 2007

AbstractThe diastereomeric ceramides, (2S,3S,4R)‐, (2S,3S,4S)‐, (2S,3R,4S)‐, and (2S,3R,4R)‐2‐[(2R)‐2‐hydroxytetracosanoylamino]‐1,3,4‐hexadecanetriols 5–8 and the corresponding ceramide lactosides 1–4 have been synthesized. Compound 1 is almost identical with the natural specimen, acanthalactoside A. The physical data of these diastereomeric compounds are most useful to determine the stereochemistry of ceramides and ceramide lactosides, either isolated from natural sources or obtained by partial hydrolysis of gangliosides.
Reactions of 3‐vinylindole derivatives with dienophiles
Authors: Medio‐Simon Mercedes , Pindur Ulf 
Published: July 2007

AbstractReactions of 3‐(1‐cyclohexenyl)‐1,2‐dimethylindole (1a) and the 1,2‐dihydrocarbazole 1b with some carbo‐ and heterodienophiles are described. Thus, compound 1a reacts to give ene, Michael‐type, and Diels‐Alder adducts, depending on the dienophile and reaction conditions. The 3‐vinylindole 1b reacts with 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione or N‐phenylmaleimide in a dehydrogenative reaction to yield the fully aromatized carbazole 8.
Sekundärstoffe aus dem chemischen Screening, 16. Inthomycine, neue Oxazol‐triene aus Streptomyces sp.
Authors: Henkel Thomas , Zeeck Axel 
Published: July 2007

Secondary Metabolites by Chemical Screening, 161). – Inthomycins, New Oxazole‐Trienes from Streptomyces sp.The oxazole‐triene metabolites inthomycin A to C (2, 4, 6) have been discovered by chemical screening in the culture broth of Streptomyces sp. (strain Gö 2). Its separation was successful only when the compounds had previously been transformed into the 3‐O‐(S)‐2‐phenylbutanoates 3, 5 and 7. The structures were deduced from their spectroscopic data, especially those taken from 2D‐NMR spectra. The natural products reveal differences in the (E/Z) configuration of its triene chains. By feeding [1‐13C]acetate to growing cultures of strain Gö 2, it was determined that C‐1 to C‐10 of the inthomycins biosynthetically originated via the polyketide pathway. Inthomycin A (2) has already been known as a substructure element of oxazolomycin (1) and probably is identical with the recently described phthoxazolin.
Preparation and use of chloromethyl (−)‐menthyl ether in the synthesis of optically pure α‐branched α‐amino nitriles
Authors: Shatzmiller Shimon , Dolithzky Ben‐Zion , Bahar Eliezer 
Published: July 2007

AbstractThe synthesis of optically pure chloromethyl (−)‐menthyl ether (2b) and its use in the synthesis of di‐(−)‐menthyl acetal (−)‐menthyl (+)‐menthyl acetals are described. The diastereomeric mixed acetals 7a, b and 8a, b are easily obtainable from the nitrones 5 and 6, KCN and 2b. The mixtures of diastereomers are separated into the pure components 7a, 7b and 8a, 8b by simple silica gel column chromatography. Hydrolysis of these products (H2O2/Na2CO3, ultrasound) followed by NO cleavage affords the heterocyclic α‐methyl‐α‐amino amides 11a, 11b and 12a, 12b. These are subsequently hydrolyzed to give the corresponding α‐methyl‐α‐amino acids with S and R configuration, respectively.
Synthesis of an enantiomerically pure sterol side‐chain precursor by enantioselective reduction of 1,3‐dihydroxy‐3‐methyl‐2‐butanone with baker's yeast
Authors: Schrötter Eberhard , Weidner Judith , Schick Hans 
Published: July 2007

Abstract1,3‐Dihydroxy‐3‐methyl‐2‐butanone (1), accessible in 5 steps from 2‐methyl‐3‐butyn‐2‐ol, is reduced by baker's yeast to (R)‐(+)‐3‐methyl‐1,2,3‐butanetriol (2) with a high enantioselectivity. This chiral building block for the synthesis of various sterols with a modified side chain thus becomes available in 73% yield with an enantiomeric excess of 90%.
5‐Imino‐1,4,5,6‐tetrahydro‐1,2,3,4‐tetrazine aus 5‐Alkyliden‐4,5‐dihydro‐1H‐tetrazolen und elektrophilen Aziden
Authors: Quast Helmut , Regnat Dieter , Balthasar Jürgen , Banert Klaus , Peters Eva‐Maria , Peters Karl , Von Schnering Hans Georg 
Published: July 2007

5‐Imino‐1,4,5,6‐tetrahydro‐1,2,3,4‐tetrazines Formed from 5‐Alkylidene‐4,5‐dihydro‐1H‐tetrazoles and Electrophilic Azides1)The electrophilic azides 1 react with the 5‐alkylidenedihydrotetrazoles 8 already at low temperatures to produce high yields of the novel 5‐iminotetrahydro‐1,2,3,4‐tetrazines 10 besides molecular nitrogen. The configurations of (Z)‐10a, (E)‐10c, (Z)‐10d, and (E)‐10h are elucidated by means of X‐ray diffraction analyses. The formation of 10 is interpreted in terms of an initial [3 + 2] cycloaddition leading to the unstable spiro compounds 9. Ring opening of their dihydro‐1,2,3‐triazole ring generates the zwitterions 11 which lose molecular nitrogen with concomitant ring expansion of the dihydrotetrazole ring by a nitrogen 1,2‐shift. The tetrazines 10a–c and e are also obtained when 8a is generated from the tetrazolium salt 7a and trapped „in situ”︁ by the azides 1a–c and e.
Synthese von C‐Glycosiden der N‐Acetylneuraminsäure und weiteren Derivaten
Authors: Paulsen Hans , Matschulat Peter 
Published: July 2007

Synthesis of C‐Glycosides of N‐Acetylneuraminic Acid and Other DerivativesReaction of the β‐pyranosyl chloride 1 of N‐acetylneuraminic acid with allyl(tributyl)stannane under radical‐induced conditions affords a mixture of the allyl C‐glycosides 2/3. After deprotection, the pure allyl α‐C‐glycoside 5 and the analogous β isomer 7 can be isolated. The allyl C‐glycosides 2 and 3 are converted into the corresponding epoxypropyl C‐glycosides 9 and 11 by epoxidation of the allylic group. Further modified allyl C‐glycosides are prepared from the C‐3‐hydroxylated N‐acetylneuraminic acid, which are available as pure α‐ and β‐C‐glycosides 19 and 21 after deprotection. At C‐3 modified compounds are also synthesized which have allyl and azido residues at C‐3. All compounds are interesting as potential inhibitors of sialidases, CMP sialate syntheses, and viral infection.