bluuebunny/crossref_metadata_2025_split huggingface dataset:
Selektive Amidspaltung bei Peptiden mit α,α‐disubstituierten α‐Aminosäuren
Authors: Wipf Peter , Heimgartner Heinz 
Published: December 2004

Selective Amide Cleavage in Peptides Containing α,α‐Disubstituted α‐Amino AcidsA new synthesis of dipeptides with terminal α,α‐disubstituted α‐amino acids, using 2,2‐disubtituted 3‐amino‐2H‐azirines 1 as amino‐acid equivalents, is demonstrated. The reaction of 1 with N‐protected amino acids leads to the corresponding dipeptide amides in excellent yield. It is shown that the previously described selective hydrolysis (HCl, toluene, 80°, or HCl, MeCN/H2O, 80°) of the terminal amide group results in an extensive epimerization of the second last amino acid. An acid‐catalyzed enolization in the intermediate oxazole‐5(4H)‐ones is responsible for this loss of configurational integrity. In the present paper, a selective hydrolysis of the terminal amide group under very mild conditions is described: In 3N HCl (THF/H2O 1:1), the dipeptide N,N‐dimethylamides or N‐methytlanilides are hydrolized at 25–35° to the optically pure dipeptides in very good yield.
Complexes of 2,2′,2″‐Nitrilotriphenol. Part 3. Crystal and Molecular Structures of Three Aluminium Complexes
Authors: Müller Edgar , Bürgi Hans‐Beat 
Published: December 2004

AbstractCrystal and molecular structures of three Al(III) complexes of the tripod ligand 2,2′,2″‐nitrilotriphenolate (I) are presented. They all show 5‐coordinate Al in approximately trigonal bipyramidal geometry, with an external nucleophile X occupying the second axial position. X is OH− in[Al(I)(OH)]−[Hquin]+ (quin = quinuclidine), N in [Al(I)(py)] (py = pyridine), and one of the O‐atoms of a second molecule in the dimeric [(Al(I))2]. Correlated variations in the axial bond lengths of the trigonal bipyramid are observed: [(Al(I))2]: Al–Nint. = 2.094 Å, Al–Oext. = 1.850 Å; [Al(I)(py)]: Al–Nint. = 2.153 Å, Al–Next., = 1.992 Å; [Al(I)(OH)]−: Al–Nint. = 2.278 Å, Al–Oext. = 1.765 Å. They are interpreted in terms of a dissociative reaction path at the Al(III) centre.
Angular Distortions at Tetracoordinate Carbon Planoid Distortions in α,α′‐Bridged Spiro[4.4]nonanes and [5.5.5.5]Fenestranes
Authors: Luef Wolfgang , Keese Reinhart 
Published: December 2004

AbstractStructures of α,α′‐bridged spiro[4.4]nonanes and [5.5.5.5]fenestranes, obtained from X‐ray analysis and MNDO calculations, are investigated in terms of symmetry‐deformation coordinates. The central C(C)4 fragments of these molecules show strong preference for compression, which is due to opening of opposite bond angles. The planoid deformations and strain energies of the fenestranes are discussed.
Mehrstufige Redoxsysteme. XLIX. Mitteilung. Mit π‐Systemen substituierte 1,3‐Dimethylidencyclobutane: Synthese und Eigenschaften
Authors: Freund Wolfgang , Hünig Siegfried 
Published: December 2004

Multistep Redox Systems. 1,3‐Dimethylidenecyclobutanes Substituted by π‐Syntheses and PropertiesAs potential redox systems 1,3‐dimethylidenecyclobutanes are synthesized in which the ‘exo’‐methylidene group participates in a cyclopentadienyl (typeC4)or cycloheptatrienyl (type A5) system. Benzo‐annellated systems are also described. The formation of the CC bond by the reaction of thioketones (3 and 31) with diazo compounds is extended to extended to 1,6,7,21, and 24, which so far had not been employed. In some cases, intermediate thiiranes can be isolated (e.g.4) which are smoothly transformed into the target compounds of types C4 and A5 by extrusion of sulfur. The new CC bonds may be introduced stepwise, thereby allowing the synthesis of unsymmetrically substituted 1,3‐dimethylidenecyclobutanes (e.g. 20 and 35). Reduction of by Na does not produce bicyclobutanes but compounds 43 and 44 with one dihydrofulvene unit.
Reaktionen von 1,2‐Bis(trimethylsilyl)iminen mit Selen‐und Tellur‐halogeniden
Authors: Neidlein Richard , Knecht Dagmar 
Published: December 2004

Reactions of 1,2‐Bis(trimethylsilyl)imines with Selenium and Tellurium HalogenidesThe reactions of benzil‐bis(trimethylsily)imine and phenanthrene‐9,10‐bis(trimethylsilyl)imine with SeOCl2, SeCl4 and TeCl4 are described.
Remote Tricarbonyl(diene)iron Substituent Effect on Ester Heterolysis. The Solvolyses of 5,6,7,8‐Tetramethylidenebicyclo[2.2.2]oct‐2‐yl Methanesulfonate and of its Tricarbonyliron Mono‐ and Dinuclear Complexes
Authors: Zwick Jean‐Christophe , Gabioud Rapny , Vogel Pierre 
Published: December 2004

AbstractBuffered acetolyses and hydrolyses of 5,6,7,8‐tetramethylidenbicyclo[2.2.2]oct‐2‐yl methanesulfonate (17), of its ‘syn‐endo’ (18), ‘syn‐exo’ (19), ‘anti‐endo’ (20), ‘anti‐exo’ (21) tricarbonyliron complexes and of its ‘anti‐exo,syn‐endo’ (22) and ‘anti‐endo,syn‐exo’ (23) bis(tricarbonyliron) dinuclear complexes have been investigated (product analysis and kinetics). In contract with the solvolyses of the uncomplexed mesylate 17, the solvolyses of the complexed esters can be highly chemo‐ and stereoselective. The nature of the products (non‐rearranged bicyclo[2.2.2]oct‐2yl vs. rearranged bicyclo[3.2.1]oct‐2‐yl derivatives) depends on the relative configuration of the tricarbonyl(diene)iron moieties and on the medium. The rates of solvolyses of 17 are only slightly affected by complexation of one or both s‐cis‐butadiene units with Fe(CO)3 groups, except in the cases where the diene moiety ‘anti’ with respect to the mesylate is complexed onto its ‘endo’ face (20,23). In these cases, significant rate‐retardation effects are observed, consistent with the inductive effect of the Fe(CO)3 substituent. Such retardation effects are overwhelmed by competing accelerating homoallylic participation by uncoordinated ‘anti’ ‐diene moieties (18,19) or, as in the case of the ‘anti‐exo’‐Fe(CO)3 complexes 21 and 22, by possible direct metal participation to the ionization process.
Ironcarbonyl Complexes of 5,6‐Dimethylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene Derivatives. Synthesis of Substituted Tricarbonyl(ortho‐quinodimethane)iron Complexes and 2‐Indanones
Authors: Bonfantini Edia , Métral Jean‐Luc , Vogel Pierre 
Published: December 2004

AbstractThe l‐dimethoxymethyl‐5,6‐dimethyldene‐7‐oxabicyclo[2.2.1]hept‐2‐ene (9) has been prepared. On treatment with Fe2(CO)9, the endocyclic double bond C(2)C(3) was coordinated first giving the corresponding exo‐Fe(CO)4 complex 10. The latter reacted with Fe2(CO)9 and afforded cis‐heptacarbonyl‐μ‐[1RS,2SR,3RS,4SR,5RS,6SR‐2,3‐η: C5,6,C‐η‐(1‐(dimethoxymethyl)‐5,6‐dimethylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene)]diiron (11) as a major product. On heating, 11 underwent deoxygenation of the 7‐oxabicyclo[2.2.1]heptene moiety yielding tricarbonyl[C,5,6,C‐η‐(1‐(dimethoxymethyl)‐5,6‐dimethylidenecyclohexa‐1,3‐diene)]iron (13). In MeOH, a concurrent, regioselective methoxycarbonylation was observed giving tricarbonyl[C,3,4,C‐η‐(methyl 5‐(dimethoxymethyl)‐3,4‐dimethylidenecyclohexa‐1,5‐diene‐1‐carboxylate)]iron (14). Oxidative removal of the Fe(CO)3 moiety in 13 and 14 did not afford the expected ortho‐quinodimethane derivatives but led to CO insertions giving 2,3‐dihydro‐2‐oxo‐1Hindene‐4‐carbaldehyde (20) and methyl 7‐formyl‐2‐3‐dihydro‐2‐oxo‐lH‐indene‐5‐carboxylate (21), respectively.
Synthesis, crystal and molecular structure of the 3:2 complex between europium nitrate and the A‐isomer of dicyclohexyln‐18‐crown‐6: Conformational study of the ligand
Authors: Nicolò Francesco , Plancherel Dominique , Bünzli Jean‐Claude G. , Chapuis Gervais 
Published: December 2004

AbstractThe crystal and molecular Structure of bis[dinitrato‐(2,5,8,15,18,21‐hexaoxatricyclo[20.4.0.09,14]hexa‐consane)europium(III)]pentakis(nitrato) europiate(III) ([Eu(NO3)2·LA]2[Eu(NO3)5]) has been determined from single‐crystal X‐ray diffraction. The complex crystallizes in the monoclinic space group P21/c (ITC No. 14): a = 13.614(3)Å, b = 21.697(4)Å, c = 22.591(5)Å, β = 107.15(2)°, Z = 4. The structure was refined to a final R value of 0.055 (Rw = 0.055). The asymmetric unit contains three independent ions with approximate C2 symmetry: [Eu(NO3)5]2− and two distinct [Eu(NO3)2.La]+ cations with the macrocyclic ligand in the cis‐syn‐cis‐conformation (A‐isomer). The Eu(III) ions are 10‐coordinated with the following mean bond lengths: EuO(nitrate) = 2.46(3)Å in the anion and the two cations, EuO(ether) = 2.55(9)Å in both cations. For the uncomplexed A‐and B‐isomers, as well as for their complexes with various metal ions, a conformational analysis has been made on the six O‐atoms of the ligand which can be considererd as a fluxional ring. In the presently reported europium complex cations, the oxygen‐ring conformation is almost a perfect boat with the metal ions lying in the least‐sqiares plane of the O‐atoms (deviation: 0.02–0.05Å). The same conformation prevails in all the complexes containing the A‐isomer(exception: dimethylthallium complex) and in most of the complexes with the B‐isomer. For this isomer, a chair conformation is found in the uncomplexed ligand, in the sodium complex, and in the complex with dimethylthallium. The occurrence of these conformations is discussed with respect to the crystallographic symmetry of the complexes and the relative mean MO and OO distances.
Synthese und Bestimmung des Chiralitätssinns von (+)‐(R)‐1‐Azabicylo[3.3.1]nonan‐2‐on
Authors: Brehm Renate , Ohnhäuser Dieter , Gerlach Hans 
Published: December 2004

Synthesis and Determination of the Chirality Sense of (+)‐(R)‐1‐Azabicyclo[3.3.1]nonan‐2‐oneOptically active (+)‐(R)‐1‐azabicyclo[3.3.1]nonan‐2‐one ((+)‐1) of known absolute configuration is synthesized in the following way: Resolution of (±)‐piperidin‐3‐ethanol ((±)‐2) by fractional recrystallization of its diastereoisomeric salts with (+)‐3‐bromocamphor‐8‐sulfonic acid from EtOH gave a less soluble salt that yielded(+)‐2. The chirality sense of (+)‐2 was shown to be (R) by chemical correlation with the enantiomers of 3‐oxocyclopentaneacetic acid ((±)‐8) of known absolute configuration. This correlation was effected by a Beckmann rearrangement of the oxime (R)‐9 to the pyridone (S)‐10 followed by a direct reduction with LiAlH4 to give the enantiomer (−)‐(S)‐2 that was characterized as its benzyloxycarbonyl derivative (−)‐(S)‐3. The alcohol (+)‐3 was converted via (+)‐4 into the nitrile (+)‐5 which gave by hydrogenolysis and hydrolysis the (R)‐configurated hydrochloride (+)‐6 which was cyclized to the bicyclic (5R)‐lactam (+)‐1 in 67% yield by heating with 2 equiv. of dibutyltin(IV) oxide in toluene. The nonplanar amide function in (+)‐1 with the substituents at the N‐atomarranged in a trigonal pyramid causes two rather intense Cotton effects at 242 (Δϵmax = +19.5) and 211 nm(Δϵmax = −17.9) in the CD spectrum. If the molecules of (+)‐1 do exist mainly in the chair‐twistboat conformation, the amide chromophore is pyramidally deformed in a sense defined by the absolute configuration at C(5). Therefore, the CD spectrum of the (5R)‐lactam (+)‐1 can be used to test theories describing the chiroptical properties of distorted amides.
Nucleotides. Part XXVIII. Chemical syntheses of the 2′‐5′‐cordycepin‐trimer core
Authors: Charubala Ramamurthy , Uhlmann Eugen , Himmelsbach Frank , Pfleiderer Wolfgang 
Published: December 2004

AbstractThe chemical synthesis of 3′‐deoxyadenyly‐(2′‐5′)‐3′‐deoxyadenylyl‐(2′‐5′)‐3′‐deoxyadenosine (30; trimeric cordycepin) is described by three different routes using various protecting groups and applying the phosphotriester approach. The intermediates have been isolated and characterized by elemental analyses and spectroscopic means. High yields of 30 have been obtained on deprotection making this biologically very active compound available in preparative scale.
The Radical Cations and the Radical Anions of Some Weitz‐Type S‐Donors
Authors: Gerson Fabian , Gescheidt Georg , Knöbel Jürgen , Murata Ichiro , Nakasuji Kazuhiro 
Published: December 2004

AbstractThe radical cations and the radical anions of 1,6‐dithiapyrene (1) and 3,10‐dithiaperylene (2) as well as those of three further Weitz‐type S‐donors 3, 4, and 5 have been studied by ESR spectroscopy. The experimental findings for (widths and behaviour on saturation of hyperfine lines) suggest that the ground state of this radical anion is effectively degenerate. With the exception of , the ESR studies of all radical ions could be complemented by the use of the ENDOR and general TRIPLE resonance techniques. In addition to proton hyperfine data, 33S coupling constants have been determined for (0.53mT), (0.46mT), and (0.34mT); they are in agreement with the predicted substantial π‐spin populations at the S‐atoms.
Condensed Heterotricycles. Synthesis and Reactions of b‐Fused 1(2H)‐Isoquinolinones with unusual enaminic properties
Authors: Nagarajan Kuppuswamy , Rao Vunnam R. , Shah Rashmi K. , Shenoy Sharada J. , Fritz Hans , Richter Wilhelm J. , Muller Dieter 
Published: December 2004

AbstractHomophthalic acid (1) undergoes reaction with 1,2‐, 1,3‐, and 1,4‐diamines to give condensed 1(2H)‐isoquinolinones like 2, 4, 13, and 25, which exhibit marked enamine character. These are attacked by electrophiles at the N or C terminus. Some notable reactions of imidazoisoquinolone 2 are those with maleic and acrylic acids to form the tetracycles 48 and 51, respectively. With propiolic acid, 5 underwent an interesting reaction to form the benzimidazonaphthyridine 53. An equally interesting behaviour was elicited from 2 in its reaction with formaldehyde, when in addition to the expected methylene‐bridged molecule 59, the novel spiro derivative 60 was formed by the dimerisation of a presumed azadiene intermediate 63.
The Adamantane Rearrangement of Tricyclo[4.2.2.01,5]decane to Tricyclo[5.3.0.04,8]decane
Authors: Ghatak Kanai L. , Ganter Camille 
Published: December 2004

AbstractRegioselective generation of the C(2)‐carbocation a of tricyclo[4.2.2.01,5]decane (1) by treatment of both corresponding epimeric alcohols 5 and 6 with BF3 and trapping the rearranged tricyclo[5.3.0.04,8]decan‐7‐yl carbocation b with Et3SiH as hydride‐ion donor (ionic hydrogenation) gives the corresponding hydrocarbon 3 as sole product in almost quantitative yield. The latter is a known intermediate in the Lewis‐acid‐catalyzed rearrangement of 1 to adamantane (4).
Complexes with a Pincers. 2,6‐Diphenylpyridine as Twofold‐Deprotonated (C ∧ N ∧ C) terdentate ligand in C,C‐trans‐, and as mono‐deprotonated (C ∧ N) chelate ligand in chiral C,C‐cis‐complexes of platinum(II) and palladium(II). Preliminary communication
Authors: Cornioley‐Deuschel Christine , Ward Thomas , Von Zelewsky Alex 
Published: December 2004

Abstract2,6‐Diphenylpyridine forms, as twofold‐deprotonated, terdentate ligand, complexes with Pt(II) and Pd(II), having two adjacent five‐membered metallocycles. As mono‐deprotonated, bidentate ligand, it forms cis‐bis‐complexes having a chirality axis. Pt(II) complexes undergo thermal and photochemical oxidative addition reactions, yielding stable Pt(IV) compounds. Pd(II) complexes yield substitued 2,6‐diphenylpyridine in photochemical reactions.
Konformationsanalysen von Modell‐Tripeptiden: Der Einfluss von α,α‐disubstituierten α‐Aminosäuren auf die Sekundärstruktur. Teil II. Röntgenstrukturanalyse und Konformationsenergie‐Berechnungen
Authors: Wipf Peter , Kunz Roland W. , Prewo Roland , Heimgartner Heinz 
Published: December 2004

Conformational Analysis of Tripeptide Models: The Influence of α,α‐disubstituted α‐Amino Acids on the Secondary Structure. X‐Ray Analysis and Conformational Energy CalculationsThe X‐ray analysis of tripeptide Z‐Ile‐Val(2‐Me)‐benzocaine (1f) reveals the presence of a type‐III β‐turn. Moreover, MMP2 calculations on tripeptides, e.g. Z‐Ile‐Aib‐benzocaine (1c), Z‐Ile‐D‐Val(2‐Me)‐benzocaine (1g), Z‐Ile‐Gly(2,2‐Pr2)‐benzocaine (1h), Z‐Ile‐Gly‐benzocaine (1a), and 1f, fit well into the frame of NMR and CD investigations. They allow considerations on the relative stability of different types of β‐turns depending on the peptide sequence, e.g. the kind of α,α‐disubstituted amino‐acid moieties.
Fluorine‐Containing Organozinc Reagents. Part III. A new formylation reaction of fluroalkylzinc halides
Authors: Lang Robert Werner 
Published: December 2004

AbstractA new Si‐induced Vilsmeier‐type formylation of F‐containing organozinc reagents is described. This two‐step process via the isolable intermediate 10 seems to be quite general for the synthesis of anhydrous polyhalogenated aldehydes.
Intramolekulare Cycloadditionen Mit Azomethin‐Yliden: Synthese und NMR‐Untersuchungen einiger Paracyclophan‐Derivate vom Makrolid‐Typ
Authors: Eberbach Wolfgang , Heinze Ingrid , Knoll Katja , Fritz Hans , Borle François 
Published: December 2004

Intramolecular Cycloaddition Reactions with Azomethine Ylides: Synthesis and NMR Investigations of Some Macrolide‐Type ParacyclophanesSeveral aziridine derivatives bearing a para‐substituted phenyl group have been prepared as precursors of azomethine ylides for intramolecular 1,3‐dipolar cycloadditions. Upon heating in refluxing toluene, the expected reactions take place resulting in the regioselective formations of the pairs of diastereoisomers 14/15 and 16/17, respectively. As indicated by the sharply decreasing yield in the a‐series (< 5%), a useful application of this method for preparing paracyclophane compounds is restricted to derivatives with more than 11 bridging atoms. The results of detailed 1H‐ and 13C‐NMR investigations with the pyrrolidino‐annulated cyclophanes are discussed with respect to the configuration at the five‐membered heterocycles and to the conformational flexibility of the bridges.
Assignment of Quaternary Carbon Atoms in 13C‐NMR Spectroscopy: Application of an improved heteronuclear 2D‐NOE experiment
Authors: Bigler Peter 
Published: December 2004

AbstractNuclear Overhauser effects (NOE) between protons and heteronuclei can be of great value for the assignment of quaternary nuclei, and they can be very informative and unique in view of stereochemistry and molecular dynamics. The application of a modified 2D‐NMR experiment for the assingment of quaternary carbon atoms of a medium‐sized molecule is demonstrated. Compared to NMR experiments designed to detect scalar instead of dipolar interactions, measuring times are considerably longer, but data analysis is in many cases more straightforward.
Pteridines. Part LXXXV. Chemical synthesis of deoxysepiapterin and 6‐acylpteridines by acyl radical substitution reactions
Authors: Baur Ralph , Sugimoto Takashi , Pfleiderer Wolfgang 
Published: December 2004

AbstractA new synthesis of deoxysepiapterin (2), one of the two yellow eye pigments of the Drosophila mutant sepia, is described. The synthetic approach makes use of a homolytic nucleophilic acylation of 7‐(alkylthio)pteridine derivatives (11, 13, 15, 18, 20) leading to the corresponding 6‐acyl derivatives ( 21–27). Desulfurizations have been achieved for the first time in the pteridine series using Raney‐Co,Raney‐Cu, or CuAl alloy in alkaline medium. Besides cleavage of the C(7)S bond, further reductions of the CO group at C(6) and the C(7)N(8) bond are detected as side reactions leading to 6‐(1‐hydroxyalkyl) (34, 35, 42, 43) and 6‐acyl‐7,8‐dihydro derivatives (2, 36, 37), respectively, The newly synthesized compounds have been characterized by elemental analysis, pK determination, UV and 1H‐NMR spectra.
exo‐Stereoselectivity in Diels‐Alder Addition of Halogenocyclopropenes to Butadienes and Furans
Authors: Müller Paul , Bernardinelli Gérald , Pfyffer Jean , Rodriguez Domingo , Schaller Jean‐Pierre 
Published: December 2004

AbstractThe stereochemistry of the Diels‐Alder reaction of 1,2‐dichloro‐3,3‐difluorocyclopropene (5a) to 1,4‐diphenyl‐1,3‐butadiene (6) and 1,3‐diphenylisobenzofuran (7) was unambiguously established by X‐ray structure determination. In all cases known so far, tetrahalogenocyclopropenes add exo to open‐chain dienes and furans. The previously reported exo‐addition product (2a) of l‐bromo‐2‐chlorocyclopropene (5b) to 7 allows assignments of the stereochemistry of other additions of 5b to furans. exo‐Addition usually predominates, but in some cases endo‐ adducts are also formed. This contrasts with reports in the literature that 5b adds preferentially endo to open‐chain dienes.
Reactions of Haloarenes with Thiolate Anions in Tetraglyme: Competition between electron transfer and SNAr mechanisms
Authors: Pastor Stephen D. 
Published: December 2004

AbstractThe reaction of the bromo‐substituted naphthalene 1 with the alkanethiolate anions 2a–b and arenethiolate 2c in tetraglyme gave the corresponding 1‐naphythyl thio‐ethers 3a–c. Thio‐ethers 3a–c were oxidized to the corresponding sulfones 4a–c with m‐ chloroperoxybenzoic acid. The reaction of the dichloro‐substituted anthracene 5a with 2b gave the disubstutution product 6a. The reaction of 9‐bromoanthracene 5c with the alkanethiolate 2b gave 6b, whereas the reaction of 5c with the arenethiolate 2c gave a mixture of substitution product 6c and anthracene 7. The observation of the formation of both 6c and 7 is explained by the competition between substitution (SnAr) and electron‐transfer (ET) mechanisms. Consistent with this interpretation, the reaction of the monochloro‐substituted 5b, which has a higher‐energy σ* orbital, with 2c gave 6c without the formation of 7. Zn/KOH in tetraglyme was shown to reduce the aryl halides 5b–c and thio‐ether 6c to 7.
Synthèse de l'acide décarboxythamnolique
Authors: Pulgarin César , Tabacchi Raffaele 
Published: December 2004

Synthesis of Decarboxythamnolic AcidThe total synthesis of the meta‐depside decarboxythamnolic ( = 3‐[(3‐formyl‐2‐4‐dihydroxy‐6‐methyl‐phenyl)oxy]‐2‐hydroxy‐6‐methoxy‐4‐methylbenzoic acid; 25) by the biomimetic condensation of the substituted β‐orcinol units 9 and 22 is described.
Synthese von enantiomerenreinen Violaxanthinen und verwandten Verbindungen
Authors: Acemoglu Murat , Uebelhart Peter , Rey Max , Eugster Conrad Hans 
Published: December 2004

Syntheses of Enantiomerically Pure Violaxanthins and Related CompoundsThe epoxides 16 and ent‐16, prepared by Sharpless‐Katsuki oxidation of 15 in excellent yield and very high enantiomeric purity, were used as synthons for the preparation of (+)‐(S)‐didehydrovomifoliol (45), (+)‐(6S, 7E, 9E)‐abscisic ester 46, (+)‐(6S, 7E, 9Z)‐abscsic ester 47, (−)‐(3S, 7E, 9E)‐xanthoxin (49), (−)‐(3R, 7E, 9E)‐xanthoxin (50), (3S, 5R, 6S, 3′S,5′R, 6′S, all‐E)‐violaxanthin (1) (3R, 5R,6S,3′R,5′R,6′S, all‐E)‐violaxanthin (55) and their (9Z) (see 53, 57), (13Z) (see 54, 58), and (15Z) (see 60) isomers. The novel violadione (61) was prepared from 1 by oxidation with DMSO/Ac2O. By base treatment, 61 was converted into violadienedione (62), a potential precursor of carotenoids with phenolic end groups.
Synthese von Orellin
Authors: Hasseberg Hans‐Albrecht , Gerlach Hans 
Published: December 2004

Synthesis of OrellineOrelline (1), a metabolite of the toadstool Cortinarius Overllauns Fries with 2,2′‐bipyridine structure, has been synthesized by the following method. The easily accessible 2‐bromo‐3‐hydroxypyridine (3) was converted into the corresponding [2‐(trimethylsilyl)ethoxy]methyl (SEM) ether 4 and coupled with Zn and NiCl2/Ph3P to form the bipyridine derivative 5 in 79% yield. Due to the chelating effect of the two SEM‐ether groups in 5, it was possible to from selectively the dilithium compound 6 by an exchange reaction with BuLi at −50° in Et2O. Reaction of 6 with electrophiles at −20° afforded the 4‐ and 4,4′‐substituted bipyridines 7–14 in excellent‐to‐reasonable yield. Oxidation of 6 with 2‐(phenylsulfonyl)‐3‐phenyloxaziridin and with bis(trimethylsilyl)peroxide gave the 4,4′‐diol 9 in 22 and 10% yield, respectively. Methanolysis of 9 directly afforded crystalline 1 in high yield, with properties identical with those of natural orelline. Formylation of 6 with N‐formylmorpholine gave 45% of the dicarbaldehyde 13. Removal of the SEM groups in 13 by hydrolysis afforded the dihydroxydicarbaldehyde 15 that could be oxidized to 1 with alkaline H2O2. Attempts to oxidize 1 to orellanine (2) with 35% H2O2 according to a known procedure were unsuccessful (cf. Exper. Part). Compound 7 with two Me3Si groups in 4,4′‐position gave after methanolysis the fluorescence dye 16 with an appreciable Stokes shift in cyclohexane.