bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ein meta‐Xylylen durch Bamford‐Stevens‐Reaktion eines Fulven‐Keten‐Addukts
Authors: Stadler Heinz , Rey Max , Dreiding André S. 
Published: December 2004

A meta‐Xylylene by Bamford‐Stevens Reaction of a Fulvene‐Ketene‐AdductHeating the sodium salt 8 of the tosylhydrazone 4 of 4‐isopropyliden‐7,7‐dimethylbicyclo[3.2.0]hept‐2‐en‐6‐one (3; obtained by the addition of dimethylketene to 6,6‐dimethylfulvene (1)), in diglyme at 130° led to the cotamethyl‐[2.2]metacyclophane 10 (17%). The latter probably was formed by dimerization of the non‐Kékulé molecule m‐xylylene 14, which, in turn, could have arisen via the homofulvene 13 from the carbene 12. A second product in the thermolysis of 8 was the tricycle 9 (9 %), as a result of an intramolecular insertion of the carbene C‐atom in 12 into a methyl C,H‐bond. Further products were the azines 11a, 11b (50%), of the type known as byproducts in Bamford‐Stevens reactions. Heating dry 8 afforded 9 (9%) and the two benzene derivatives 15 (9%) and 16 (3%). The tosylhydrazone 4 could be recovered by reaction of 11a, 11b with p‐toluenesulfonohydrazide.
Dimers of 3,7‐dehydrotropones (bicyclo[3.2.0]hepta‐1(7),2,4‐trien‐6‐ones)
Authors: Szechner Barbara , Rey Max , Dreiding André S. , Grieb Rita 
Published: December 2004

Abstract2‐(tert‐Butyl)‐3,7‐dehydrotropone (7‐(tert‐butyl)bicyclo[3.2.0]hepta‐1(7),2,4‐trien‐6‐one; 1) was found to dimerize reversibly to 2A by [2 + 4]‐cycloaddition/cycloreversion reaction. The equilibrium lies on the side of the highly strained dimer 2A in the solid state, and on the side of the monomer 1 in solution. The [2 + 4]‐reaction is fully perisite‐, regio‐ and stereoselective. Above room temperature, 1 irreversibly formed a decarbonylated dimer 6, probably via the intermediate 9A or 9B, which resulted either from a dimerisation of 1 by [4 + 6]‐cycloaddition or from a sigmatropic rearrangement of the originally formed dimer 2A or 2B. Similary, the 6‐bromo derivative 14 afforded the corresponding decarbonylated dimer 15. Should the formation of 6 and 15 be due to a primary cycloaddition then that reaction is fully peri‐, site‐ and regioselective. Mild LiAlH4‐reduction of 6 and subsequent acetylation yielded the acetate 11, the structure of which was established by an X‐ray analysis. More vigorous LiAlH4‐treatment also reduced the terminal fulvenoid double bond of 6 and acetylation of the crude product led to the acetated 12 and 13.
Preparation of Regioselectively Protected Hydroquinones by Phosphorylation of p‐Benzoquinones with Trialkyl Phosphites
Authors: Duthaler Rudolf O. , Lyle Paulette A. , Heuberger Christoph 
Published: December 2004

AbstractThe title reaction has been applied to 10 monosubstituted p‐benzoquinones (Scheme 2, Table). The regioselectively of the O‐phosphorylation is influenced by bulky substituents (t‐butyl and trimethylsilyl) and, electronically, by the methoxy group. The regioselectivity, which is high in nonpolar media (benzene), is lower in polar solvents (CH2Cl2) and (CH3CN). The synthetic potential of this transformation, exemplified by the preparation of compounds 29 (Scheme 3) and 32 (Scheme 4), is considerably extended by applying milder methods for the phosphate hydrolysis and by using the reagent couple P(OCH3)3/trimethylsilyl chloride, which gives clean access to p‐hydroxyphenyl phosphates. p‐Benzoquinones 4th and 4i with strong π‐acceptor substituents react in a different way, giving phosphonates. The electronically induced regioselectivity of the O‐phosphorylation is in according with the preferences expected for the attack by a nucleophilic phosphorylation agent.
Messkette zur direkten potentiometrischen Bestimmung des Enantiomerenüberschusses von 1‐Phenyläthylmmonium‐Ionen
Authors: Bussmann Walter , Morf Werner E. , Vigneron Jean‐Pierre , Lehn Jean‐Marie , Simon Wilhelm 
Published: December 2004

AbstractCell Assembly for the Potentiometric Determinatin of the Enantiomeric Excess of 1‐Phenylethylammonium‐IonsA cell assembly with two membranes containing each one enantiomer of the ionophor N,N,N′,N′,N″,N″,N‴,N‴‐octabutyl‐1,4,7,10,16‐hexaoxacyclooctadecane‐2,3,11,12‐tetracarboxamide is used for the direct potentiomewtirc determination of the enantiomeric excess ee of 1‐phenylethylammonium ions in aqueous solutions. The preference for the (R)‐over the (S)‐1‐phenylethylammonium ion by the (2R,3R,11R,12R)‐ionophor of 2.7 allows a reliable determination of ee even in the presence of known concentrations of the heavy interferent KCl.
Deoxy‐nitrosugars, 7th communication Synthesis of methyl shikimate and of diethyl phosphashikimate from D‐ribose
Authors: Mirza Sohail , Vasella Andrea 
Published: December 2004

AbstractThe chain elongation of the deoxy‐nitroribose 6 by a Michael addition to the vinyl‐phosphonate 7 followed by a solvolysis gave the heptulosephosphonate 11 (87%). From 11, the key intermediates 15 and 16 (77%) were obtained by a highly diastereoselective reduction, followed by detritylation, periodate cleavage, and silylation. Methoxycarbonylation of 15 and 16 gave 17 and 18 which were converted into methyl shikimate (21; 79%) by intramolecular olefination and partial deprotection. Similarly, phosphonoylation of 16 gave 22 (99%) which was transformed into the diethyl phosphashikimate 2 (53% from 6).
The Persistence of Ribbon Orbitals in Polycyclic Alkanes
Authors: Heilbronner Edgar , Honegger Evi , Zambach Werner , Schmitt Peter , Günther Harald 
Published: December 2004

AbstractEquivalent bond orbital (EBO) calculations by a procedure based on recalibrated, localized bond orbitals derived from an ab initio model, suggest that the two frontier ‘ribbon’ orbitals φHOMO, φHOMO‐1 of polycyclic hydrocarbons consisting of all‐trans‐connected six‐membered rings are well separated in energy from the remaining manifold of σ‐orbitals. Assuming the validity of Koopmans' theorem, a PE‐spectroscopic investigation of perhydroanthracenes, 2‐methylperhydrophenalene and perhydroperylene have shown that this is indeed the case. According to the theoretical treatment these ribbon orbitals are evenly delocalized over the whole of the molecular frame and they conserve the characteristic phase relationship postulated by Hoffmann et al. [16] for cyclohexane moieties. Their behaviour under the successive introduction of centres of unsaturation, i.e., of double bonds is discussed.
A New Pyranocoumarin Diester from Polygala paniculata L
Authors: Hamburger Matthias , Hostettmann Kurt , Stoeckli‐Evans Helen 
Published: December 2004

AbstractA new coumarin diester has been isolated from Polygala paniculata L. (Polygalaceae) by a combination of flash chromatography on silica gel and preparative reversed‐phase chromatography. Its structure has been determined as 3′‐O‐acetyl‐4′‐O‐benzoylkhellactone (= 9‐acetoxy‐9,10‐dihydro‐8,8‐dimethyl‐2‐oxo‐2 H,8H‐benzo[1,2‐b:3,4‐b′]dipyranh‐10‐yl benzoate) by spectroscopic methods (UV, IR, 1H‐NMR, EI‐and CI‐MS) and by X‐ray analysis.
Experiments on the total synthesis of Lysolipin I. Part II. Michael addition of 1,3‐cyclohexanedione to quinone acetals
Authors: Duthaler Rudolf O. , Wegmann Urs H.‐U. 
Published: December 2004

AbstractBase‐catalyzed reaction of 1,3‐cyclohexanedione (3) with the quinone monoacetals 4 and 7 leads to the polycyclic products 5 and 8, respectively, and in the case of 4 to variable amounts of dibenzofuranone 6. The 2‐arylcyclohexanedione 9, on the other hand, is isolated from the reaction of 3 and bisacetal 11 catalyzed by ZnCl2 (Scheme 2). Treatment of the adduct 8 with (CH3O)2SO2/K2CO3 results in cleavage of teh heterocyclic ring by a retro‐Michael reaction affording teh liable enone 23 which was further transformed to 24 by selective hydrogenation. The 8‐acetoxydibenzofuranone 22 is obtainable from 8 by acid treatment and acetylation (Scheme 4). The reactions of the silylenol ethers 27 and 35 with quinone monoacetals were very complex (Scheme 6). The desired arylcyclohexanone derivatives 28 and 36 were formed in very low yields. Under certain conditions (elevated temperature or strong Lewis acids as catalysts), single‐electron transfer or addition to the ene‐acetal rather than to the enone function of the quinone monoacetals became predominant. In connection with this study, the sensitive 2‐methoxy‐p‐benzoquinone monoacetals 15 (Scheme 3) and 29 (Scheme 6) have been prepared and characterized.
Experiments on the total synthesis of Lysolipin I. Part III. Preparation and transformations of substituted 1,2,3,4‐Tetrahydrodibenzofuran‐1‐ones
Authors: Duthaler Rudolf O. , Scherrer Veronica 
Published: December 2004

Abstract1,2,3,4‐Tetrahydrodibenzofuran‐1‐ones were obtained by Michael addition of 1,3‐cyclohexadione (2) to o‐benzoquinone (3) and to p‐benzoquinones 8 and 11 (Scheme 2). In addition to the expected 7,8‐disubstituted adduct 14, the ZnCl2‐catalyzed reaction of dione 2 with methoxy‐p‐benzoquinone (11) afforded a small amount of the 6,8‐disubstituted regio‐isomer 13 (Scheme 2). The projected cleavage of these dibenzofuranones to 3‐methoxy‐2‐phenyl‐2‐cyclohexenone 22 could be effected by treatment with NaOH followed by methylation (Scheme 3). Attempted acetalization of such dibenzofuranones resulted in a retro‐Claisen‐type cleavage, giving the benzofuryl‐butyrate 16. Other transformations include reduction of the ketone, of the C(4a)=C(9b) bond, and alkylation with Li‐ethoxyacetylide (Scheme 3). Oxidation of 8‐hydroxy‐7‐mehoxydibenzofuran derivatives led to o‐quinones instead of the desired ring cleavage to p‐quinones (Scheme 4).
Photoreaction of (RS,SR)‐3‐Phenyl‐6‐hepten‐2‐ol. Benzene‐Olefin Cycloadditions as a Synthetic Route to [5.5.5.5] Fenestranes. Part III
Authors: Mani Jürg , Cho Jung‐Hyuck , Astik Rameshchandra R. , Stamm Erich , Bigler Peter , Meyer Veronika , Keese Reinhart 
Published: December 2004

AbstractIrradiation of (RS,SR)‐3‐Phenyl‐6‐hepten‐2‐ol (3n) gave the photoproducts 6n–10n. Some reactions of 6n and 8n are reported. The regio‐ and diastereoselectivity observed in the photoreaction of substituted 5‐phenylpentenes is discussed with respect to conformational preferences of the compounds to be irradiated.
The Reaction of 4‐Hydroperoxy‐2,4,6‐trimethylcyclohexa‐2,5‐dienone with Acetaldehyde. Formatino of the Bis(peroxyacetal)
Authors: Jefford Charles W. , Bernardinelli Gérald , McGoran Ernest C. 
Published: December 2004

AbstractThe reaction of 4‐hydroperoxy‐2,4,6‐trimethylcyclohexa‐2,5‐dienone with acetaldehyde using trimethylsilyl trifluoromethanesulfonate as catalyst gives 1,1′‐bis[(1,3,5‐trimethyl‐4‐oxo‐2,5‐cyclohexadienyl) peroxy]diethyl ether (7) in 70% yield. The structure of this unusual acetal was determined by X‐ray analysis.
Approaches to the synthesis of cytochalasans. Part 7. Synthesis of some building blocks for the construction of the macrocyclic moiety
Authors: Wallach Daniel , Csendes Ivan G. , Burckhardt Peter E. , Schmidlin Tibur , Tamm Christoph 
Published: December 2004

AbstractThe synthesis of ethyl (2E, 4E, 8R)‐8‐methyl‐10‐[(2H‐tetrahydropyran‐2‐yl)oxy]‐2,4‐decadienoate (11), methyl (2E, 8R)‐8‐methyl‐10‐[(2H‐tetrahydropyran‐2‐yl)oxy]‐2‐decenoate (16), synthons for the construction of the macrocyclic moieties of the cytochalasins A, B and F, and of (3R)‐[7‐(1,3‐dioxolan‐2‐yl)‐3‐methylheptyl]triphenyl‐phosphonium bromide (24), a C8‐building block for deoxaphomin, proxiphomin and protophomin is described. In all instances (+)‐(R)‐pulegone (5) served as starting material.
Approaches to the synthesis of cytochalasans. Part 8. Further transformations and optical resolution of the tetrahydroisoindolinone subunit
Authors: Schmidlin Tibur , Wallach Daniel , Tamm Christoph 
Published: December 2004

AbstractThe bicycle aldehyde 7 was prepared from the hydroxy ester 3 for the attachment of teh macrocyclic moiety of the cytochalasans. To protect the C(6),C(7)‐double bond the intermediates 8, 9 and 13 were transformed into the epoxides 10, 11 and 14, respectively. Treatment of 10 and 11 with Al(i‐PrO)3 gave the allylic alcohol 12. Protection of the olefinic double bond was also effected by hydroxylation with OsO4. The triol 17 obtained from 3, after acetalization of 18, was oxidized to the aldehyde 20. Attachment of the ylide of the phosphonium salt 1 to 20 gave 24, an intermediate of proxiphomin (2). Removal of the C(6), C(7)‐diol group was achieved via the thiocarbonate 23.
Milde alkalische Hydrolyse von Aconitin
Authors: Katz Alfred , Rudin Hanspeter 
Published: December 2004

Mild Alkaline Hydrolysis of AconitineHydrolysis of aconitine (1) with 0.04N K2CO3 in 90% MeOH at room temperature yields, besides the alkamine aconine 3 considerable amounts of 8‐O‐methylaconine (6) and smaller quantities of desbenzoyl‐pyroaconitine (4) and 16‐epi‐desbenzoyl‐pyroaconitine (5). Better yields of 4 and 5 are obtained when heating a solution of aconitine in 0.04N K2CO3 in 90% EtOH.
Synthese eines 2,5,7,10‐substituierten 1,6‐Methano[10]annulens, seine Methylierung, Ätherspaltung und Deprotonierung
Authors: Neidlen Richard , Hartz Georg 
Published: December 2004

AbstractSynthesis of a 2,5,7,10‐Substituted 1,6‐Methanol[10]annulene, its Methylation, Ether Cleavage; and DeprotonationThe synthesis of 2,7 ‐di(tert ‐butoxy)‐1,6‐methanol[10]annulene derivatives 2 and 3 are described. Methylation of 3 gave 4, and 4 was transformed, on treatment with p‐toluene sulfonic acid, to the salt 5. Basic reagents deprotonated 5; the resulting solution was analyzed by 1H‐NMR spectroscopy.
Herstellung enantiomerenreiner cis‐ oder trans‐konfigurierter 2‐(tert‐Butyl)‐3‐methylimidazolidin‐4‐one aus den Aminosäuren (S)‐Alanin, (S)‐Phenylalanin, (R)‐Phenylglycin, (S)‐Methionin und (S)‐Valin
Authors: Naef Reto , Seebach Dieter 
Published: December 2004

Preparation of the Enantiomerically Pure cis‐ and trans‐Configurated 2‐(tert‐Butyl)‐3‐methylimidazolidin‐4‐ones from the Amino Acids (S)‐Alanine, (S)‐Phenylalanine, (R)‐Phenylglycine, (S)‐Methionine, and (S)‐ValineIn contrast to α‐hydroxy and α‐mercapto carboxylic acids, simple α‐amino acids do not form acetal‐type derivatives (2, X = NH) with pivalaldehyde. For the generation of amino‐acid‐derived chiral, nonracemic enolates (cf. 3), and hence, for the α‐alkylation of amino acids without racemization and without an external chiral auxiliary, the imidazolidinones 12–14 were prepared diastereoselectively. To this end, the methyl or ethyl esters of amino‐acid hydrochlorides were first converted to N‐methylamides of amino acids which in turn were condensed with pivalaldehyde to give (neopentylidenamino)amides (11). These Schiff bases could be cyclized either to trans‐or to cis‐imidazolidinones (12, 14 and 13, respectively), which were obtained in enantiomerically pure form after recrystallization. The enantiomeric purities were confirmed by HPLC with chiral stationary phases or by 1H‐NMR spectroscopy in the presence of chiral shift reagents. The configurations (cis, trans) were assigned by NOE measurements on 300‐ or 360‐MHz 1H‐NMR spectrometers.
Synthèse électrochimique de complexes Ni(O)‐diazabutadiène
Authors: Coulombeix José , Emmenegger Franz‐Peter 
Published: December 2004

Electrochemical Synthesis of the Ni(O)‐Diazabutadiene ComplexesThe electrochemical reduction of Ni salts in the presence of diazabutadiene ligands (DAB = RNCHCHNR, R = t‐Bu, o‐xylyl, p‐anisoyl, p‐tolyl) has been studied in DMF by cyclic voltammetry and rotating disc polarography. In solutions containing DAB and halide X−, Ni(II) can be reduced to Ni(DAB)2, and the features of this reduction agree with a mechanism where the second DAB replaces X− in the coordination sphere of Ni only after its reduction to Ni(O). Rather concentrated (≃ 0.1M) solutions of NiBr2 · DME and DAB in DMF have been electrolyzed without a supporting electrolyte, making the isolation of the product Ni(DAB)2 particularly easy. Thus, gram quantities of Ni(DAB)2 can be conveniently prepared within a few hours.
Molluscicidal Saponins from Talinum tenuissimum DINTER
Authors: Gafner Frank , Msonthi Jerome D. , Hostettmann Kurt 
Published: December 2004

AbstractTwo new saponins, β‐D‐glucopyranosyl 3‐O[O‐βD‐xylopyranosyl‐(1→3)‐O‐(β‐D‐glucopyranosyluronic acid)]oleanolate (1) and 3‐O‐[O‐β‐D‐xylopyranosyl‐(1→3)‐O‐(β‐D‐glucopyranosyluronic acid)]oleanolic acid (2), have been isolated from the tubers of Talinum tenuissimum. The structures have been established mainly by 13C‐NMR and FAB‐MS. The monodesmosidic saponin 2 exhibits very strong molluscicidal activity against the schistosomiasis‐transmitting snail Biomphalaria glabrata.
Propellanes. Part LXXX. Baeyer‐Villiger Oxidation of [4.3.3]Propellane‐8,11‐dione
Authors: Ashkenazi Pnina , Kapon Moshe , Piantini Umberto , Philipsborn Wolfgang Von , Ginsburg David 
Published: December 2004

AbstractOxidation of the title compound with m‐chloroperbenzoic acid affords a keto‐lactone, two bis‐lactones and a bis‐spirolactone, in varying amounts depending upon the reaction conditions. The structures were established by means of X‐ray diffraction, 1H‐ and 13C‐NMR spectroscopy.
Synthese substituierter Cyclononatetraene
Authors: Sabbioni Gabriele , Neuenschwander Markus 
Published: December 2004

Synthesis of Substituted CyclononatetraenesIn the course of an exploration of possible synthetic pathways to nonafulvenes, a series of 1‐substituted cyclononatetraenes (CNT) 4b–1 have been prepared in yields of about 60%. Their structures follow from spectroscopic data as well as from the quantitative valence isomerisation to 1‐endo‐substituted cis‐3a, 7a‐dihydroindenes 8. Both all‐cis‐CNT− 1 and cis,cis,cis,trans‐CNT− 2 have been used as nucleophiles. Whereas 2 is normally more nucleophilic than 1, the yield of cyclononatetraenes 4 prepared with 2 may be reduced due to by‐products such as 9 and 10.
Polar effects. Part 12. Inductivity and carbon participation in the solvolysis of 4‐substituted 2‐adamantyl arenesulfonates
Authors: Grob Cyril A. , Wittwer Gerhard , Rama Rao K. 
Published: December 2004

AbstractThe rate constants (log k) for the solvolysis of 4e‐substituted 2e‐ and 2a‐adamantyl p‐nitrobenzenesulfonates 14 and 15, respectively, in 80% EtOH correlate linearly with the respective inductive substituent constants σ. Therefore, relative rates are controlled by the I effect of the substituents at C(4). The derived reaction constants, or inductivities, ρI of −0.80 and −0.64 for the series 14 and 15, respectively, are far smaller than those previously determined for 6‐substituted 2‐norbornyl and 2‐bicyclo[2.2.2]octyl sulfonates, in which the partial structure containing the substituent and the leaving group is the same. The ratio of the retained and inverted adamantanols obtained upon hydrolysis of the series 14 falls from 2.85 for R = CH3 to ca. 1 for R = CN, i.e. as the substituent at C(4) becomes more electron‐attracting. In the 2a‐series 15 this ratio is uniformly higher. These findings confirm that the 2‐adamantyl cation is weakly bridged and that through‐space induction in carbocations involves graded bridging of the cationic center by neighboring C‐atoms.
Conjugated Biradical Intermediates: Spectroscopic, Kinetic, and Trapping Studies of 2,2‐Dimethyl‐1,3‐perinaphthadiyl
Authors: Hasler Erich , Gassmann Ernst , Wirz Jakob 
Published: December 2004

AbstractThe biradical 2,2‐dimethyl‐1,3‐perinaphthadiyl (a) was generated from two different precursors, the naphthocyclopropane 1 and the azo compound 2, and from each by three different pathways (pyrolysis, direct photolysis, and triplet sensitization, Scheme 1). The combined evidence from flash photolysis, low‐temperature spectroscopy, and product analyses provides a detailed mechanistic picture of the formation and decay of this reactive intermediate which is persistent at 77 K in the triplet ground state (3a) and rather long‐lived (400 μs) at room temperature. When formed in its lowest singlet state (1a), the biradical is too short‐lived to undergo intersystem crossing to 3a or bimolecular reactions. Thus, 3a is formed exclusively from the excited triplet state of the precursor compounds, 31* or 33*. The monomolecular decay of 3a is retarded by the spin barrier; 3a initiates the polymerization of acrylonitrile and is trapped by 3O2.
Aromatic nucleophilic substitution. Part 2. Preparation of novel 3‐substituted xanthone and thioxanthone derivatives
Authors: Fischer Walter , Kvita Vratislav 
Published: December 2004

AbstractThe novel 3‐nitro‐9‐oxo‐9H‐xanthene‐ and 3‐nitro‐9‐oxo‐9H‐thioxanthene‐l‐carboxylic acids 2a–d were prepared by intramolecular acylation of 3‐aryloxy‐ and 3‐arylthio‐5‐nitrophthalic anhydrides 1 (Scheme). The 3‐nitro group was readily substituted by O‐ and S‐nucleophiles and halide and azide ions to give a range of 3‐substituted thioxanthone derivatives 3 with varied λmax.
Chinazolincarbonsäuren. VII. Mitteilung. Ein einfacher Zugang zu (4‐Oxo‐3,4‐dihydrochinazolin‐3‐yl)‐alkansäuren, (4‐Oxo‐3,4‐dihydro‐1,2,3‐benzotriazin‐3‐yl)‐alkansäuren und deren Estern
Authors: Süsse Manfred , Johne Siegfried 
Published: December 2004

Quinazoline Carboxylic Acids. An Easy Route to (4‐Oxo‐3,4‐dihydroquinazolin‐3‐yl)‐alkanoic Acids, (4‐Oxo‐3,4‐dihydro‐1,2,3‐benzotriazin‐3‐yl)‐alkanoic Acids and their EstersA new route was found for the synthesis of (4‐Oxo‐3,4‐dihydroquinazolin‐3‐yl)‐alkanoic acids (8) and (4‐Oxo‐3,4‐dihydro‐1,2,3‐benzotriazin‐3‐yl)‐alkanoic acids (6) by cyclization of the N‐(2‐aminobenzoyl)amino acids 5 with HCOOH or HNO2. 2H‐3,1‐Benzoxazine‐2,4(1H)‐diones (1) reacted with glycine esters to 2, which were cyclized by HNO2 to the esters 4. Ester 4 was hydrolyzed to 6 (X = CH2). Diones 1 reacted with the most common amino acids (as the ammonium salt of tertiary amine) to amino‐alkanoic acids 5, which were cyclized with orthoformate to 7 or 8 depending on the reaction conditions.
Reactivité de composés carbonylés avec des cétènes en présence d'alkoxydes de titane ou de zirconium. 3e communication
Authors: Hofer Roger , Evard Daniel , Jacot‐Guillarmod André 
Published: December 2004

Reactivity of Carbonyl Compounds with Ketenes in the Presence of Titanium or Zirconium AlkoxidesThe reaction of ketene or dimethylketene with aldehydes or ketones in the presence of titanium or zirconium alkoxides gives essentially β‐hydroxyesters. By polyinsertion of ketene and aldehydes in the TiO bond, di‐ tri‐ and tetraesters are formed. An excess of ketene produces acetyl derivatives of esters and 6‐alkyl‐3,4,5,6‐tetrahydro‐2,4‐pyrandiones.
Totalsynthese von (–)‐Norgestrel
Authors: Baier Helmut , Dürner Gerd , Quinkert Gerhard 
Published: December 2004

Total‐Synthesis of (–)‐Norgestrel(–)‐Norgestrel (1a) or (–)‐norethindrone (1b), two active progestational ingredients of currently used contraceptives have been synthesized stereoselectively. Compound 1a has been obtained starting from m‐cresol methyl ether, dimethyl malonate, and (E)‐1,4‐dibromo‐2‐butene. The steroid skeleton has been constructed using an intramolecular Diels‐Alder reaction of an o‐quinodimethane derivative preceeded by a photo‐enolization of an appropriate methyl‐substituted acetophenone derivative. Chirality has been introduced at an early stage during an ScN′ reaction (cf. Scheme 1). Compound 1b has been obtained similarly using a previously reported mixture of the enantiomerically pure constitutional isomers 18b/19b (cf. Scheme 3).