bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solvolysen von 4‐Alkylidenbicyclo[3.2.0]hept‐2‐en‐6‐olen. Synthese von 1‐Vinylfulvenen und 8,8‐Diphenylheptafulven
Authors: Stadler Heinz , Rey Max , Dreiding André S. 
Published: December 2004

Solvolysis of 4‐Alkydenbicyclo[3.2.0]hept‐2‐en‐6‐oles. Synthesis of 1‐Vinylfulvenes and 8,8‐DiphenylheptafulveneFour 4‐alkylidenebicyclo[3.2.0]hept‐2‐en‐6‐ones 2–5, obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ ‐alcohols ‘endo’‐6 to ‘endo’‐9 (68–73%) and ‘exo’‐6 to ‘exo’‐9 (3–20%). Treatment of some of these alcohols with (CF3SO2)2O in CH2Cl2/pyridine caused a spontaneous solvolysis to yield unsaturated 7‐membered rings as pyridinium triflates 10–12 or 1‐vinylfulvenes 13 and 14, a new class of reactive tetraenes: Both ‘endo’‐9 and ‘exo’‐9, having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H‐atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’‐6 to ‘endo’‐8 afforded only the corresponding 7‐membered‐ring pyridinium salts 10–12 (66–79%), while ‘exo’‐6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)‐bond cleavage with ‘endo’‐B and ‘endo’–6‐‘endo’‐8, as well as the C(1), C(7)‐bond cleavage with ‘exo’‐B, ‘exo’‐6, and with both ‘endo’‐ and ‘exo’‐9. Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3‐isopropenyl‐cycloheptatrienes 18 and 19, respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8‐diphenylheptafulvene (23, 86%) was obtained.
Selektive Herstellung von l‐ oder u‐Aldolen aus Äthyl‐trityl‐keton und aromatischen Aldehyden über Lithium‐ bzw. Aluminium‐Enolate
Authors: Ertaş Mümtaz , Seebach Dieter 
Published: December 2004

Selective Preparation of l‐ or u‐Aldols from Ethyl Trityl Ketone and Aromatic Aldehydes through Lithium and Aluminium Enolates, RespectivelyThe ethyl trityl ketone (1) is deprotonated to the (Z)‐enolate 2 which adds to aromatic aldehydes with relative topicity ul to give the aldols 3(−78°, THF, kinetic control). If, on the other hand, 1 is heated with trimethylaluminium in toluene, the aluminium enolate formed combines with aromatic aldehydes and with cinnamic aldehyde with opposite relative topicity (lk) to the aldols 5 (+20°, toluene, 2 d, precipitation of the aluminium aldolate 4, thermodynamic control). The mechanism is discussed (cf. Fig. 1). The adducts to benzaldehyde (3a, 5a), furfural (3f, 5f), and cinnamaldehyde (3i, 5i) are O‐(2‐methoxyethoxy)methyl (MEM) protected and cleaved by lithium triethylborohydride to the 1,3‐diol derivatives 9–11 with a free primary and a protected secondary OH‐group. Analogous conversions of 1 and other ketones may also be diastereoselective, but turned out to be of less preparative value (see 6–8, 12).
Intramolekulare 1,3‐dipolare Cycloadditionen von Diarylnitriliminen aus 2,5‐Diaryltetrazolen
Authors: Meier Hansruedi , Heimgartner Heinz 
Published: December 2004

Intramolecular 1,3‐Dipolar Cycloadditions of Diaryl‐nitrile‐imines Generated from 2,5‐Diaryl‐tetrazolesAlkenyl‐substituted diaryl‐nitrile‐imines – generated by photolysis or thermolysis of alkenyl‐substituted 2,5‐diaryl‐tetrazoles ‐ undergo a regioselective intramolecular [2 + 3] cycloaddition to yield new heterocyclic compounds, e. g. fused 2‐pyrazolines. With alkinyl derivatives, the corresponding pyrazoles have been formed. UV evidence is given for the intermediate nitrile‐imine at − 190°. The latter can be trapped using an excess of carboxylic acid (UV evidence for a new intermediate at − 120°). In this case, the corresponding rearranged addition product N′‐acyl‐N′‐aryl‐benzohydrazide is isolated in good yield.
Radicaux libres dérivés de sucres. Partie. VII. Analogues de nucléosides marqués par un spin. Communication préliminaire
Authors: Tronchet Jean M. J. , Mekhael Kamal , Graf‐Poncet Joëlle , Benhamza Rachid , Geoffroy Michel 
Published: December 2004

Sugar Free Radicals. VIII. Spin‐Labeled Nucleosides AnalogsA series of 5′‐deoxy‐5′‐hydroxylamino derivatives of adenosine and uridine have been prepared by reduction of the corresponding oxime or nitrone. ‘Second generation’ 3′‐deoxy‐3′‐N‐aryl(or N‐alkyl) hydroxylamino‐β‐D‐xylofuranosyluracils have also been synthesized by a one‐pot reaction including the following elementary steps: deblocking of the starting material, reduction of the 3′‐deoxy‐3′‐oximinouridine, condensation of the resulting hydroxylamine with an aldehyde, reduction of the nitrone formed. The deoxy‐hydroxylaminonucleosides oxidized spontaneously in the air (or in presence of traces of PbO2) to give the corresponding nitroxide free radicals, ESR spectra of which furnished useful informations on their structures. Some of these modified nucleosides bore notable cytotoxic or antiviral activities.
Synthèse d'une nouvelle depsidone dérivée de l'acide furfurique, le diméthoxy‐3,8‐(diméthoxy‐2,4‐méthoxycarbonyl‐5‐diméthyl‐3,6‐benzyl)‐9‐triméthyl‐1,4,6‐oxo‐11‐11H‐dibenzo[b,e]dioxépinne[1,4]carboxylate‐7 de méthyle
Authors: Gunzinger Jan , Tabacchi Raffaele 
Published: December 2004

Synthesis of a New Depsidone, Derivative of Furfuric Acid: Methyl 3,6‐dimethoxy‐9‐(2,4‐dimethoxy‐5‐methoxycarbonyl‐3,6‐dimethylbenzyl)‐1,4,6‐trimethyl‐11‐oxo‐11H‐dibenzo[b,e] [1,4]dioxepin‐7‐carboxylateThe total synthesis of the title compound 1b is described. Starting from simple orcinol and β‐orcinol units, the benzophenone 4 has been prepared. Using a biomimetic reaction, the intramolecular oxydative coupling, lead to the grisadienedione 25. By thermal interconversion and permethylation, the depsidone 1b has been obtained.
Neue Synthese von Vinblastinderivaten; 20′‐Deethyl‐20′‐deoxyvinblastin und 20′‐Deethyl‐20′‐deoxy‐C′‐homovinblastin Vorläufige Mitteilung
Authors: Schill Gottfried , Priester Claus Ulrich , Windhövel Udo Frank , Fritz Hans 
Published: December 2004

A New Synthesis of the Vinblastine Derivatives 20′‐Deethyl‐20‐deoxyvinblastine and 20′‐Deethyl‐20′‐deoxy‐C′‐homovinblastineA new synthesis of vinblastine derivatives is described. In the key step, the chloroindolenine derivative 14 was reacted with vindoline (2) to give, after cyclization, stereospecifically 17/I and 20′‐deethyl‐20′‐deoxyvinblastine (17/II). In an analogous manner, the epimeric C′‐homovinblastine derivatives 21/I‐21/IV were synthesized.
Anion Selectivity of Metalloporphyrins in Membranes
Authors: Ammann Daniel , Huser Marin , Kräutler Bernhard , Rusterholz Bruno , Schulthess Peter , Lindemann Bernhard , Halder Ernst , Simon Wilhelm 
Published: December 2004

AbstractLipophilic Co(III) and Mn(III) complexes of 5,10,15,20‐tetrakis[4‐(hexyloxycarbonyl)phenyl]porphyrin act as positively charged carriers for anions and induce anion selectivities in membranes clearly deviating from the sequence of classical anion exchangers. Different anion selectivities are observed for the Co(III) and Mn(III) porphyrins.
Pteridine. Teil LXXXI. Mechanismus der Photooxidation von 5,6‐Dihydro‐1,3‐dimethyl‐6‐thioxopteridin‐2,4(1H,3H)‐dion
Authors: Heckel Armin , Pfleiderer Wolfgang 
Published: December 2004

Mechanism of the Photooxidation of 5,6‐Dihydro‐1,3‐dimethyl‐6‐thioxopteridine‐2,4(1H,3H)‐dioneThe mechanism of the photooxidation of 5,6‐dihydro‐1,3‐dimethyl‐6‐thioxopteridine‐2,4(1H,3H)‐dione (9) has been investigated in dependence of the pH. Photooxidation of the anion species in weak alkaline solution takes place by singlet oxygen as well as the superoxide radical anion forming 1,2,3,4‐tetrahydro‐1,3‐dimethyl‐2,4‐dioxopteridine‐6‐sulfinate (5) as the first detectable reaction product. In acidic medium, a more complex photooxidation process is observed leading, in a radical‐chain mechanism, to 6,6′‐dithiobis[1,3‐dimethylpteridine‐2,4(1H,3H)‐dione] (6).
Synthèse d'acétals de désoxy‐3‐hydroxyamino‐3‐furannoses. Note de laboratoire
Authors: Tronchet Jean M. J. , Habashi Ford , Fasel Jean‐Pierre , Zosimo‐Landolfo Guido , Barbalat‐Rey Françoise , Moret Gilles 
Published: December 2004

Synthesis of 3‐Deoxy‐3‐(hydroxyamino)furanose AcetalsReduction of sugar ketoximes with NaBH3CN under acidic conditions constitutes a good synthetic pathway to deoxy(hydroxyamino)sugar derivatives. These compounds which are useful building blocks for the preparation of analogs of various classes of biologically important carbohydrates are reasonably stable.
Fragmentation of Optically Active (1‐Phenylethyl)‐ and (1‐Naphthylethyl)ureas in Refluxing Alcohols: Easy Preparation of Optically Active Amines of High Optical Purity
Authors: Schönenberger Bernhard , Brossi Arnold 
Published: December 2004

Abstract(1‐Phenylethyl)‐ and (1‐naphthylethyl)ureas, obtained in the reaction of racemic amines with optically pure isocyanates, are separated and then decomposed in refluxing alcohols, to afford optically pure secondary amines and optically pure alkyl carbamates in quantitative yields. The scope of this fragmentation for the resolution of racemic mixtures of amines is illustrated by several examples of biologically important compounds. Carbamates obtained by this fragmentation can readily be recycled.
Nonapentafulvalen
Authors: Escher André , Neuenschwander Markus 
Published: December 2004

Nonapentafulvalene(1) has been prepared by oxidative coupling of sodium cyclopentadienide (6) and sodium cyclononatetraenide (7) with CuCl2 in THF, two‐fold deprotonation of cyclopentadienyl‐cyclononatetraene 8 to give dianion 16, and oxidative treatment of 16 with CuCl2 (Schemes 2 and 3). Compound 1 is a highly reactive and thermally instable molecule, since valence isomerisation 1 → 17 proceeds easily even at low temperature (the half‐life of 1 is ca. 30 min at −15° in CDCl3). NMR investigations show that nonapentafulvalene is an olefinic molecule with strongly alternating bond lengths, its nine‐membered ring deviating strongly from planarity. Comparison of the NMR data of 1 with those of a series of sterically similar pentafulvenes 18 and nonafulvenes 19 (Tables 1 and 2) demonstrates that (a) with regard to the pentafulvene unit of 1, the cyclononatetraene ring acts as very weak electron‐donating group, while (b) with regard to the nonafulvene unit of 1, the cyclopentadiene ring acts as weak electron‐accepting group. So nonapentafulvalene may be regarded as a ‘nonafulvene of inverse π‐polarisation’.
Monoterpenoid chemistry. Part 3.. Stereoselective synthesis of the major oxygenated metabolites of trans‐sobrerol
Authors: Pellegata Renato , Dosi Ivana , Ventura Paolo , Villa Maurizio , Lesma Giordano , Palmisano Giovanni 
Published: December 2004

AbstractThe stereoselective synthesis of the major oxygenated metabolites of trans‐sobrerol (1) in optically active and/or racemic form is described.
Complexes of 2,2′,2″‐Nitrilotriphenol. Part 1. A Study of Bimolecular Nucleophilic Substitution at the Boron Atom
Authors: Müller Edgar , Bürgi Hans‐Beat 
Published: December 2004

AbstractThe tetradentate ligand 2,2′,2″‐nitrilotriphenol forms a boron complex III with an intramolecular, transannular N→B dative bond of 1.68 Å in a strained tricyclo[3.3.3.0]undecane chelating system. The complex reacts with nitrogen bases L, such as pyridine, quinuclidine and others, to form complexes III‐L, in which the intramolecular B–N bond is replaced by one between B and the external nucleophile. In solution, this displacement reaction is reversible. It was studied by temperature‐dependent NMR spectroscopy. The resulting reaction and activation parameters suggest that the reaction is a bimolecular nucleophilic substitution (SN2).
The Hydrolysis of Ethyl 1‐Methyl‐2,4‐cyclopentadiene‐1‐carboxylate by Nonenzymatic and Enzymatic Methods. Carbon‐Carbon vs. Carbon‐Oxygen Bond Cleavage
Authors: Burger Ulrich , Erne‐Zellweger Dominique , Mayerl Christa 
Published: December 2004

AbstractThe title ester 5 is shown to undergo C–C bond cleavage under the conditions of basic ester hydrolysis (KOH/EtOH) with formation of potassium ethyl carbonate (6) and the tautomeric methylcyclopentadienes 7 and 8. In contrast, porcine liver esterase (PLE, EC 3.1.1.1) cleanly hydrolyses 5 to give the isolable 1‐methyl‐2,4‐cyclopentadiene‐1‐carboxylic acid (13). The latter undergoes thermal dimerization with conservation of the geminal‐substitution pattern. The configuration of the Diels‐Alder adduct 17 is ascertained by it photochemical transformation into bishomocubane dicarboxylic acid 12, easily distinguished by its C2 symmetry. Under the conditions of acid‐catalyzed hydrolysis, dimerization of ester 5 and polymerization prevail, unless low acid concentration is used. The dimer 9 of 5 has one ester function that is reluctant to undergo basic hydrolysis.
Synthesis of biopterin from neopterin? The formation of pyrrolo[1,2‐f]pteridins upon side‐chain activation of neopterin
Authors: Kaiser Ado , Wessel Hans Peter 
Published: December 2004

AbstractThe formation of derivatives of L‐neopterin (2) is investigated with respect to a possible transformation into L‐biopterin (1). High‐yield syntheses of isopropylidene and benzylidene derivatives 5 and 7, respectively, are described. Activation of the primary C‐atom in the side chain of neopterin leads to formation of pyrrolo[1,2‐f]‐pteridins via oxonium‐ion intermediates.
Synthetic Models of the Active Site of Cytochrome P‐450. 1st Communication. The Synthesis of a Doubly‐Bridged Iron(II)‐Porphyrin Carrying a Tightly Bound Thiolate Ligand
Authors: Stäubli Beat , Fretz Heinz , Piantini Umberto , Woggon Wolf‐Dietrich 
Published: December 2004

AbstractThe doubly‐bridged iron(II)‐tetraphenylporphyrin derivative 6, carrying a sterically fixed S− ligand in the ‘proximal’ position and the substrate at the ‘distal’ site, was synthesised as an enzyme model for cytochrome P‐450. Compound 36, the CO complex of 6, displays a split Soret band (403 and 457 nm) similar to the native cytochrome P‐450.
Stereoselective Syntheses of Tetrahydrolipstatin and of an Analogue, Potent Pancreatic‐Lipase Inhibitors Containing a β‐Lactone Moiety
Authors: Barbier Pierre , Schmeider Fernand , Widmer Ulrich 
Published: December 2004

AbstractTetrahydrolipstatin (1) and itsanalogue 2 are representatives of a new class of pancreatic‐lipase inhibtors. Two stereoselective synthetic approaches are described.
Diels‐Alder‐Reaktionen von 2′‐substituierten 3‐Vinyl‐1H‐indolen zu neuen anellierten Indol‐und Carbazol‐Derivaten
Authors: Pfeuffer Ludwig , Pindur Ulf 
Published: December 2004

Diels‐alder Reactions of 2′‐Substituted 3‐Vinyl‐1H‐indoles to New Annellated Indole and Carbazole DerivativesNew regio‐ and stereoselcctive cycloadditions between 2′‐ substituted 3‐vinyl‐lH‐indoles and the dienophiles N‐Phenylmaleimide, dimethyl acetylendicarboxylate, and methyl acrylate are reported. Products include some new carbazole derivatives and Michael adducts. In the presence of AlCl3 as dicnophile‐activating catalyst, ‘endo’ preference for deriving cycloadducts is observed. In some cases, Michael addition competes with[4+2] cycloaddition.
The Ionization Energies of Tetrazinodi(heteroarenes)
Authors: Lecoultre Jacques , Heilbronner Edgar , Eichenberger Thomas , Balli Heinz 
Published: December 2004

AbstractThe ionization energies of four [1,2,4,5]tetrazinodi(heteroarenes) of C2h Symmetry have been measured by PE spectroscopy. It is found that the first ionization energy is very low (6.2 eV to 6.4 eV) and rather independent of the size and/or topology of the molecules. This is explained, by comparison with the results of a simple MO treatment, as being due to strong localization of the HOMO (of Au symmetry) on the [1,2,4,5]tetrazino moiety of the molecules. The PE‐spectroscopic data are shown to be in agreement with the UV/VIS‐and electrochemical‐oxidation data published previously.
Die Position 5 im Oxotremorin‐Gerüst: Eine zentrale Stelle für die Steuerung der Aktivität am muscarinischen Rezeptor
Authors: Amstutz René , Closse Annemarie , Gmelin Gernot 
Published: December 2004

Position 5 at the Oxotremorine Skeleton as the Stearing Position for Activity at the Muscarinic ReceptorsSubstitution of the Ch2 group at position 5 of oxotremorine (2) by electronegative atoms like O‐ or N‐atom, or by sterically bulkier groups like methyl, N‐formyl, or N‐acetyl Changes the pharmacological profile of oxotremorine drastically. The O‐ and N‐analogues were potent but unselective (M1/M2) muscarinic agonists. The methyl analogue ((R)‐BOK‐1) is a muscarine antagonist which is 10 times more potent on the ganglion cervical superius (pA2 = 9.3) than pirenzepine and is able to distinguish between the ileal and ganglion receptor by a factor of 100. The N‐formyl derivative differentiates between the two receptors by a factor of 500 with a potency comparable to pirenzepine. The two M1‐selective antagonists have higher affinity to the rat‐ganglion receptors compared to the affinity to rat‐cortex homogenate. The synthesis and the pharmacological activity of several new oxotremorine analogues are discussed.
Isolation and Absolute Configuration of β,β‐Carotene Diepoxide
Authors: de Almeida Ligia Bicudo , De Vuono Camargo Penteado Marilene , Britton George , Uebelhart Peter , Acemoglu Murat , Eugster Conrad Hans 
Published: December 2004

AbstractThe 5,6:5′,6′‐diepoxy‐5,6:5′,6;‐tetrahydro‐β,β‐carotene, isolated from tubers of a white‐fleshed variety of sweet potato (Ipomoea batatas LAM.) has been assigned the (5R,6S,5′R,6′S)‐chirality on the basis of its HPLC, UV/VIS, and CD data.
Anwendung der Azirin/Oxazolon‐Methode in der Peptid‐Chemie: Synthese von Modell‐Tripeptiden
Authors: Wipf Peter , Heimgartner Heinz 
Published: December 2004

The Azirine/Oxazolone Method in Peptide Chemistry: Synthesis of Tripeptide ModelsTripeptides 5, containing an α,α ‐disubstituted α‐amino acid and ethyl p‐aminobenzoate, were synthesized in high yield by application of the azirine/oxazolone method (Table 2). In this versatile approach for the incorporation of disubstituted residues into the peptide chain, N‐protected peptides or amino acids are coupled with 2,2‐dialkyl‐3‐amino‐2H‐azirines and, after the selective hydrolysis of the newly formed C‐terminal amid bond, further condensed with amino components via in situ generated oxazole‐5(4H)‐ones in the presence of additives (Scheme 1). A comparison with conventional procedures clearly demonstrates the advantages of this new method that works equally well with β‐branched, cyclic, or acyclic disubstituted amino acids.
Silicon‐Directed Nazarov Cyclizations. Part VI. The anomalous cyclization of vinyl dienyl ketones
Authors: Denmark Scott E. , Hite Gary A. 
Published: December 2004

AbstractReactions, of various vinyl dienyl ketones (see la–e, li) with FeCl, give rise to β,γ‐unsaturated α‐vinyl‐cyclo‐pentenones (see 2a–e, 2i, Table 2). The reaction succeeds for vinyl dienyl ketones with substituents on either double bond. Aryl dienyl and alkyl dienyl ketones (see 1f–h) do not cyclize cleanly. The effects of substituents on the rate of reaction is discussed in terms of the mechanism of the rearrangement. A 13C‐labeling study establishes the pathway as an unusual 1‐hydroxypentadienyl‐cation electrocyclization to a cyclopentenyl cation which collapses via a pinacol rearrangement to the α‐vinyl ketone.
Norbornanes. Part 20. Inductivity and bridging in 2‐norbornyl cations
Authors: Bielmann Rolf , Fuso Francesco , Grob Cyril A. 
Published: December 2004

AbstractThe solvolysis rates and products of several 1‐substituted 2exo‐ and 2‐endo‐norbornyl p‐toluenesulfonates 7 and 8, respectively, have been determined. Hydrolyses of these epimeric tosylates yielded rearranged products in varying amounts, except when the substituent was COOCH3 or CN. The logarithms of the rate constants (log k) for the endo‐series 8 correlated linearly with the corresponding inductive constants σ with a reaction constant ρI of −1.24. On the other hand, log k values for the exo‐series 7 appear to fit two regression lines, the first line (ρI = −1.90) defined by the tosylates that ionize, with rearrangement, to the tertiary cations 11, the second (ρI = −1.86) by the tosylates 7 (R = H, COOCH3, and CN) that ionize to an asymmetrically bridged secondary cation 19. These results confirm the unique participation of C(6) with a ρI of −2.00 in the ionization of 2‐exo‐nor‐bornyl tosylate.
Photochemical Reactions. 149th Communication. Photochemistry of 7,8‐dihydro‐4‐hydroxy‐β‐ionone and derivatives
Authors: Pascual Alfons , Bischofberger Norbert , Frei Bruno , Jeger Oskar 
Published: December 2004

AbstractThe photolysis of 7,8‐dihydro‐4‐hydroxy‐β‐ionone (6) was investigated together with its acetate and isopropyl ether 7 and 8, respectively. Irradiation (λ > 245 nm) of 6 in MeCN or i‐PrOH at temperatures between 25° and −65° leads to the tricyclic ethers 9, 10 and 13A + B, and to the spirocyclic ethers 11 and 12, which are all known types of photoproducts, previously obtained on photolysis of 7,8‐dihydro‐β‐ionone (1). The same types of products are obtained on irradiation of the acetate 7 and the isopropyl ether 8. On the other hand, irradiation of the hydroxy compound 6 in MeCN or i‐PrOH at temperatures between −35° and −65° leads to the new tricyclic tertiary alcohols 14 and 15 as the major products. Their formation involves an intramolecular trapping of a carbocation by the neighbouring OH group, thus, supporting the previously proposed mechanism of the transformation 1 → 5. For structure proof, the tricyclic alcohol 14 and the pheny1 carbamate 42, derived from 9, were subjected to X‐ray analysis.
A new synthesis of N‐acetylneuraminic acid
Authors: Csuk René , Hugener Martin , Vasella Andrea 
Published: December 2004

AbstractA new synthesis of N‐acetylneuraminic acid (Neu5Ac; 28) via aldehyde 10 is described. The aldehyde 10 was obtained from N, acetyl‐D‐glucosamine (11; 5 steps, overall yield ca. 6%) or from D‐glucono‐1,5‐lactone (17; 6 steps, overll yield ca 57%). Thus, on the one hand, N‐acetyl‐D‐mannosamine (12), obtained from 11, was transformed into the known dithioacetal 14 and hence into the (ethylthio)dihydrooxazole 16, which was cleaved under weakly acidic conditions to the aldehyde 10. On the other hand, the known ester 18, obtained from 17, was sulfonylated and further transformed via the azide 20 into the N‐acetyl‐D‐mannonate 22. Reduction of 22 to 23 and oxidation of 23 with ‘periodinane’ again gave 10. The aldehyde 10 was treated with the organozinc reagent 8 obtained from tert‐butyl 2‐(bromomethyl)acrylate (2) to yield predominantly 24, which was transformed (two steps) into the 2‐methylidene‐D‐glycero‐nononic acid 27 and hence into Neu5Ac (28).