bluuebunny/crossref_metadata_2025 huggingface dataset:
Ring‐Open Analogues of Adenine Nucleoside. Aminoacyl Derivatives of Cyclo‐ and Acyclo‐Nucleosides
Authors: Hakimelahi Gholam H. , Zarrinehzad Morteza , Jarrahpour Ali A. , Sharghi Hashem
Published: December 2004

The synthesis of acyclic analogues of ribo‐ and deoxyribonucleosides is described. These compounds (Table 3) are both poor substrates and poor inhibitors of adenosine deaminase. The synthesis of dinucleotides from these analogues is also described, and the activity along with the inhibitory properties of some of them are studied against deaminase enzyme. These nucleotides are resistant to degradation by phosphodiesterases. HCl impregnated on silica gel is an excellent reagent for the preparation of the chloromethyl ether precursors of acyclo‐nucleosides. A general and rapid procedure is developed for the preparation and isolation of the 5′‐aminoacyl derivatives of robo‐ and arabinonucleosides. Quinoline has a marked effect on aminoacylations without racemization. Compounds 35a, b possess remarkable antiviral effects in vitro. A procedure is also developed for the conversion of acyclo‐ribonucliosides 13e, f to acyclo‐deoxyribonucleosides 11e, f.
Data bank: The PE Spectra of Paracyclophanes with Unsaturated Bridges and of Related Molecules
Authors: Yang Zhong‐Zhi , Kovač Branka , Heilbronner Edgar , Lecoultre Jacques , Chan Chin Wing , Wong Henry N. C. , Hopf Henning , Vögtle Fritz
Published: December 2004

The PE spectroscopic data for a series of [2.2]paracyclophanes with olefinic and/or aromatic bridges, and of a few related molecules are reported, together with tentative assignments based on simple MO models.
Neuartige Triterpen‐Lactone aus Helenium autumnale L.
Authors: Matusch Rudolf , Häberlein Hanns
Published: December 2004

Novel Triterpene Lactones of Helenium autumnale L.

Three novel triterpene lactones 1–3 could be detected by investigating a pentane extraxt of the Helenium autumnale L. (Asteraceae) roots. The structures are especially elucidated by 1H‐ and 13C‐NMR spectroscopy. The lactones 1‐3 formally represent Diels‐Alder products of a reaction between a sesquiterpene lactone and an α,β‐unsaturated sequiterpene aldehyde.
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 Acids

A 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

Crystal 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

Structures 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 Properties

As 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 Halogenides

The 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

Buffered 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

The 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

The 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‐one

Optically 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

The 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

The 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

Homophthalic 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

Regioselective 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

2,6‐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 Calculations

The 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.
Synthèse d'un thiophospholipide apparenté au PAF
Authors: Garrigues Bernard
Published: December 2004

Synthesis of a New PAF‐Related Thiophospholipid

A new thiophospholipid 8, related to platelet activating factor (PAF), has been synthesized with a seven‐step procedure.
Fluorine‐Containing Organozinc Reagents. Part III. A new formylation reaction of fluroalkylzinc halides
Authors: Lang Robert Werner
Published: December 2004

A 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 Paracyclophanes

Several 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

Nuclear 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

A 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

The 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

The 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 Acid

The 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 Compounds

The 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 Orelline

Orelline (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.
Applications of ENDOR Spectroscopy to Radical Cations in Freon Matrices. Part 1. The radical cation of s‐trans‐buta‐1,3‐diene
Authors: Gerson Fabian , Qin Xue‐Zhi
Published: December 2004

Precise values of the proton coupling constants have been determined from the ENDOR spectra of the radical cation of s‐trans‐buta‐1,3‐diene generated from the neutral compound by γ irradiation in a CFCl3 matrix at 77 K. These values are 1.119 and 1.050 mT for the pairs of exo‐ and endo‐protons in the 1,4‐positions, respectively, and 0.283 mT for the pair of protons in the 2,3‐positions. A general TRIPLE resonance spectrum proves that all coupling constants have the same sign which should be negative by theory, Evidence by experiment and theory indicate that the s‐trans‐configuration of the neutral compound is retained upon ionization.
(Benzylthio)‐ und (Arylthio)‐substituierte Nitril‐ylide: Thermische Erzeugung und Reaktionen
Authors: Wipf Peter , Prevo Roland , Bieri Jost H. , Germain Gabriel , Heimgartner Heinz
Published: December 2004

Thermal Generation and Reactions of (Benzylthio)‐and (Arylthio)‐Substituted Nitrile Ylides

Thermolysis of 4‐(benzylthio)‐ and 4‐(arylthio)‐1,3‐oxazol‐5(2H)‐ones 6, at 110–155° in the presence of dipolarophiles with activated C≡C, CC, CO, CS, and NN bonds, led to 5‐membered cyclo‐adducts and CO2 (cf. Schemes 3, 5‐7). Heating 6a and 6c in the presence of ethyl propiolate yielded ethyl quinoline‐3‐carboxylate (19) and ethyl pyridine‐3‐carboxylate(22), respectively (cf. Scheme 8). These results are rationalized on the basis of the intermediate formation of thio‐substituted nitrile ylides of type 7 (cf. Scheme 2), which undergo regioselective 1,3‐dipolar cycloadditions with reactive dipolarophiles. In the absence of such a dipolarophile, the nitrile ylides isomerize via a [1,4]‐H shift to give 2‐aza‐1,3‐butadienes of type 20. The latter are trapped in a Diels‐Alder reaction with ethyl propiolate (cf. Scheme 8).
The Reversible Proxibarbal‐Valofan Isomerisation. Part II. Kinetic studies in a biphasic octanol/water system
Authors: Wittekind H. Harald , Testa Bernard , Estreicher Jurek
Published: December 2004

The tautomerisation between proxibarbal (I) and the two diasterloisomers of valofan (IIX and IIY) was investigated at pH 7.4 in a biphasic octanol/H2O system. The rate constants of isomerisation and the equilibrium constants of (partition coefficients) were calculated by compartmental analysis. The rate constants of isomerisation were comparable with those determined in monophasic aqueous solutions, whereas at pH 7.4 and 37° the duration necessary for a global equilibrium to be reached was 4–6 times longer in the biphasic system. These reduced rates and the higher lipophilicity of IIX and IIY as compared to I may be of pharmacokinetic and pharmacodynamic significance. They may also have relevance for a number of drugs known or suspected to form lactonic or lactamic metabolites.
Die röntgenstrukturanalysen von (E)‐ und (Z)‐2‐Buten‐1,4‐diyl‐dithiocyanat bei 93 K
Authors: Belaj Ferdinand , Huber Stefan , Neier Reinhard
Published: December 2004

The X‐Ray Diffraction Analysis of (E)‐ and (Z)‐2‐Butene‐1,4‐diyl Dithiocyanate

The crystal structure of the (E)‐ and (Z)‐2‐butene‐1,4‐diyl dithiocyanate (1 and 2, respectively) which have been used as substrates for an E′ reaction, has been determined by X‐ray analysis. The SCN groups are for both molecules in an anticlinal conformation relative to the double bond. A remarkable intermoecular contact has been observed between the N‐atom of one molecule and the S‐atom of its neighbour.
Tandem Diels‐Alder Reactivity Controlled by Remote Substituents. Regioselective synthesis of linearly annellated six‐membered ring systems from (1RS,5SR,6RS,7SR)‐6,7‐bis(chloromethyl)‐8,9‐dimethylidene‐2‐oxabicyclo[3.2.2]nonan‐3‐one. Crystal structure of (1RS,5RS,6SR,11RS)‐6,7‐bis(chloromethyl)‐3‐oxo‐2‐oxatricyclo[7.4.0.1,5]tridec‐8‐en‐11‐yl methyl ketone
Authors: Demarchi Bernard , Vogel Pierre , Pinkerton Alan A.
Published: December 2004

Synthess of 6,7,8,9‐tetramethylidene‐2‐oxabicyclo[3.2.2]nonan‐3‐one (12), 6,7,8,9‐tetramethylidene‐2‐azatricyclo[3.2.2]nonan‐3‐one (13), and (1RS,5SR,6RS,7SR)‐6,7‐bis(chloromethyl)‐8,9‐dimethylidene‐2‐oxabicyclo‐[3.2.2]nonan‐3‐one (14) are presented. The rate constants of the two successive Diels‐Alder additions of a given dienophile to 12 and 13 were nearly the same. Lewis‐acid‐catalyzed Diels‐Alder addition of methyl vinyl ketone to 14 gave adduct 39 with high regio‐ and stereoselectivity. Lewis acids isomerized 39 into(1RS,5RS,6SR,7SR,11RS)‐6,7‐bis(chloromethyl)‐3‐oxo‐2‐oxatricyclo[7.4.0.01,5]tridec‐8‐en‐11‐yl methyl ketone (40) whose structure was determined by single‐crystal X‐ray crystallography. Heating 39 with CsF/Cs2CO3 in DMF/HMPT gave (1RS,5RS,11RS)‐6,7‐dimethylidene‐3‐oxo‐2‐oxatricycl. [7.4.0.01,5]tridec‐8‐en‐11‐yl methyl ketone (42). The exocyclic butadiene moiety of triene 42 added to methyl propynoate and 2,3‐didehydroanisole with good regioselectivity giving polysubstituted anthracenyl and naphthacenyl derivatives, respectively.
Studies on the Biosynthesis of Iridals and Cycloiridals
Authors: Marner Franz‐Josef , Gladtke Dieter , Jaenicke Lothar
Published: December 2004

The incorporation of [2‐14C]acetate, [2‐14C]mevalonate, and [3H]squalene proved the squalenoid nature of the iridals, novel triterpenoids from rhizomes of swordlilies. Methionine is readily incorporated into cycloiridalls of Iris pallida dalmatica, thus indicating that the methylation of iridals via S‐adenosyl‐L‐methionine leads to the formation of the irone moiety of the bicyclic compounds. The 3H/14C ratio of the transferred labelled methyl group remained unchanged. Therefore, the methylation/cyclization of the terpenoid side chain of iridals must proceed by a concerted mechanism without formation of a cyclopropanoid intermediate.
Photocycloadditions of 2‐(trimethylsilyloxy)‐1,3‐butadiene to 2‐cycloalkenones. Access to the basic pentalenolactone skeleton
Authors: Demuth Martin , Pandey Bipin , Wietfeld Bernhard , Said Hadi , Viader José
Published: December 2004

The [2 + 2] Photocycloaddition of 2‐(trimethylsilyloxy)‐1,3‐butadiene to a number of 2‐cycloalkenones proved to be quite a general reaction leading to good yields of the cycloadducts (Table). This finding is surprising since dienes, in general, are better known as quenchers of enone triplets rather than as photochemical reactants. Both the high substrate concentrations, which can be employed in these cycloadditions, and the remarkable regio and stereoselectivity of the processes qualify them as valuable for syntheses. In a first application, the photoproducts 1a, b were transformed in three steps into a viable precursor 4 of the pentalenolactone‐G and ‐H antibiotics.
Reaktionen des Cumalinsäure‐methylesters und Cumalinaldehyds mit ambidenten Nucleophilen
Authors: Kvita Vratislav , Sauter Hanspeter , Tuck Brian
Published: December 2004

Reactions of Methyl Coumalate and Coumalaldehyde with Ambident Nucleophiles

Methyl coumalate and coumalaldehyde show great diversity in their reactions with ambident nucleophiles both depending upon the 2H‐pyran‐2‐one derivative and the nature of the ambident nucleophile used. The products are either pyridine or pyrimidine derivatives.
Solid‐Phase Synthesis of Oligodeoxynucleotides containing phosphoramidate internucleotide linkages and their specific chemical cleavage
Authors: Bannwarth Willi
Published: December 2004

Oligonuclecotides bearing phosphoramidate internucleotide linkages can be prepared chemically by standard solid‐phase DNA synthesis. Thus, phosphoramidate internucleotide bonds can be placed at will into specific positions within a given DNA fragment. The backbone‐modified DNA fragments prepared in this way are susceptible to a specific chemical cleavage.
Struktur und Partialsynthese von dimerem Coleon F
Authors: Rüedi Peter
Published: December 2004

Structure and Partial Synthesis of Dimeric Coleon F

Coleon F (1a), on standing in solution, slowly dimerizes to the labile C(7)‐epimeric spiro‐dihydrofuranes 2a/2b whose structures were elucidated by spectroscopic methods. Oxydative addition of 1a to another molecule of 1a in the presence of Fétizon's reagent rapidly yields 2a/2b, thus confirming their structures as (4bS,9RS,10′aS)4,4a,10′,10′a‐tetrahydro‐1′,6‐dihydroxy‐1,2,4a,7′,8′,10′a‐hexamethyl‐3′,7‐bis(2‐propenyl)‐spiro[3H,9H‐phenanthren‐9,5′‐5′H‐phenanthro[1,10‐bc]furan]‐2,3,5,8,9′‐pentone.
Syntheses of Amino‐dideoxyallose and Amino‐deoxyribose Derivatives Using Acylnitroso Dienophiles
Authors: Defoin Albert , Fritz Hans , Geffroy Guillaume , Streith Jacques
Published: December 2004

The dimethyl acetals 4 of (E)‐2,4‐pentadienal and of (E,E)‐ and (E,Z)‐2,4‐hexadienals undergo regio‐ and stereospecific cycloaddition reactions with in‐situ‐generated acylnitroso dienophiles 5a and 5b, leading thereby to the corresponding dihydrooxazines 7a–d and 8c–d. cis‐Glycolization of these latter adducts stereospecifically gave the dihydro derivatives 9a–d and 10d which, after sequential hydrogenolysis, deacetalization, and instant cyclization, led to the aminodeoxyribose derivatives 17a, 17f, and 18, and to the amino‐dideoxyallose compounds 17c and 17h. These piperidino‐deoxysugar derivatives exhibit a strong anomeric effect, i.e. OHC(1) is always axial, which is explained in terms of a nN(π)‐σ*(COH) orbital compression, as compared to the less pronounced one in the more classical pyranose series.
N‐(1,3‐Thiazol‐5(4H)‐yliden)amine aus 1,3‐dipolaren Cycloadditionen von Aziden mit 1,3‐Thiazol‐5(4H)‐thionen
Authors: Pekcan Sare , Heimgartner Heinz
Published: December 2004

N‐(1,3‐Thiazol‐5(4H)‐ylidene)amines via 1,3‐Dipolar Cycloaddition of Azides and 1,3‐Thiazol‐5(4H)‐thiones

Organic azides 5 and 4,4‐dimethyl‐2‐phenyl‐1,3‐thiazol‐5(4H)‐thione (2) in toluene at 90° react to give the corresponding N‐(1,3‐thiazol‐5(4H)‐ylidene)amines (= 1,3‐thiazol‐5(4H)‐imines) 6 in good yield (Table). A reaction mechanism for the formation of these scarcely investigated thiazole derivatives is formulated in Scheme 3: 1,3‐Dipolar azide cycloaddition onto the CS group of 2 leads to the 1:1 adduct C. Successive elimination of N2 and S yields 6, probably via an intermediate thiaziridine E.
1,3‐Dipolare Cycloaddition aromatischer Nitril‐ylide und Nitril‐oxide an Dicyan und Diazocyanide
Authors: Ried Walter , Fulde Maria
Published: December 2004

1,3 Dipolar Cycloaddition of Aromatic Nitrile Ylides and Nitrile Oxides with Cyanogen and Diazocyanides

Nitril ylides 2 generated from the imidoyl chlorides 1 react with cyanogen and aryldiazocyanides to 2,5(4)‐dia‐ryl‐1H‐imidazole‐4(5)‐carbonitriles 3a,b or 5(4)‐(arylazo)‐2,4(5)‐diaryl‐1H‐imidazoles 4a and 2,3,5‐triaryl‐2,3‐dihydro‐1H‐1,2,4‐triazole‐1‐carbonitriles 5a–f, respectively (Scheme 1). Reactions of benzonitrile oxides 7 with these dipolarophiles lead to 3,3′‐diaryl‐5,5′‐bi[1,2,4]oxadiazoles 8a–c or 3‐aryl‐5‐(arylazo)‐1,2,4‐oxadiazoles 9a–j (Scheme 2).
(all‐E)‐12′‐Apozeaxanthinol, Persicaxanthine und Persicachrome
Authors: Märki‐Fischer Edith , Eugster Conrad Hans
Published: December 2004

(all‐E)‐12′‐Apozeanthinol, Persicaxanthine, and Persicachromes

Reexamination of the so‐called ‘persicaxanthins’ and ‘persicachromes’, the fluorescent and polar C25‐apocarotenols from the flesh of cling peaches, led to the identification of the following components: (3R)‐12′‐apo‐β‐carotene‐3,12′‐diol (3), (3S,5R,8R, all‐E)‐ and (3S,5R,8S,all‐E)‐5,8‐epoxy‐5,8‐dihydro‐12′‐apo‐β‐carotene‐3,12′‐diols (4 and 5, resp.), (3S,5R,6S,all‐E)‐5,6‐epoxy‐5,6‐dihydro‐l2′‐apo‐β‐carotene‐3,12′‐diol =persicaxanthin; (6), (3S,5R,6S,9Z,13′Z)‐5,6‐dihydro‐12′apo‐β‐carotene‐3,12′‐diol (7; probable structure), (3S,5R,6S,15Z)‐5,6‐epoxy‐5,6‐dihydro‐12′‐apo‐β‐carotene‐3,12′‐diol (8), and (3S,5R,6S,13Z)‐5,6‐epoxy‐5,6‐dihydro‐12′‐apo‐β‐carotene‐3,12′‐diol (9). The (Z)‐isomers 7–9 are very labile and, after HPLC separation, isomerized predominantly to the (all‐E)‐isomer 6.
Potentiometric and spectrophotometric titration of Cu2+ complexes with N‐isopropyl‐2‐methyl‐1,2‐propanediamine
Authors: Kaderli Susan , Zuberbühler Andreas D. , Kansikas Jarno
Published: December 2004

The complexation of Cu2+ by N‐isopropyl‐2‐methyl‐1,2‐propanediamine (L) has been studied by potentiometric and spectrophotometric titration. The dominant complexes formed in this system are [CuL]2+, [CuL2]2+, [Cu2L2(OH)2]2+, and [CuL(OH)2]. The data were thoroughly tested for different models with [CuL(OH)]+, [CuL(OH)]+, [Cu(OH)]+, and [Cu2(OH)2]2+ as additional species. The importance of steric factors is indicated by the d‐d* spectra: for [CuL2]2+, (λmax = 499 nm) the absorption maximum is shifted by 50 nm to high energies relative to [Cu(en)2]2+, (λmax = 549 nm), whereas the opposite is true for the 1:1 complexes ([CuL]2+ : λmax = 712 nm,s [Cu(en)]2+ : λmax = 660 nm).
Conventional and Laser Photolysis of a Bisdiazo Compound
Authors: Hannemann Klaus , Wirz Jakob , Riesen Andreas
Published: December 2004

Entirely different product distributions were observed when the bisdiazo compound 1 was irradiated by a conventional lamp (254 nm) on the one hand and by a pulsed excimer laser (248 nm) on the other. Continuous photolysis gave a complex reaction mixture (Scheme 2), of which eight products were identified. Pulsed laser photolysis gave (11E)‐dibenzocyclooctatriene 20 as a new product in 49% yield (Scheme 4). We postulate that compound 20 is formed via the biscarbene intermediate 18 which results from the sequential absorption of two photons by a single molecule within a single laser pulse.
Synthesis of Esters of 3‐(2‐Aminoethyl)‐1H‐indole‐2‐acetic Acid and 3‐(2‐aminoethyl)‐1H‐indole‐2‐malonic acid (= 2‐[3‐(2‐aminoethyl)‐1H‐indol‐2‐yl]propanedioic acid) 4th communication on indoles, indolenines, and indolines
Authors: Mahboobi Siavosh , Bernauer Karl
Published: December 2004

Alkyl 3‐(2‐aminoethyl)‐1H‐indole‐2‐acetates 6a and 6b are synthesized starting from methyl 1H‐indole‐2‐acetate (2) via methyl 3‐(2‐nitroethenyl)‐1H‐indole‐2‐acetate (4) and the alkyl 3‐(2‐nitroethyl)‐1H‐indole‐2‐acetates 5a and (Scheme 1). Analogously, diisopropyl 3‐(2‐aminoethyl)‐1H‐indole‐2‐malonate 20b is obtained from diisopropyl 1H‐indole‐2‐malonate 11c (Scheme 4). An alternative synthesis of 20a and 20b follows a route via 15–18 and the dialkyl 3‐(2‐azidoethyl)‐1H‐indole‐2‐malonates 19a and 19b, respectively (Scheme 3). The aminoethyl compounds 6a and 20a are easily transformed into lactams 7 and 21, respectively. Procedures for the preparation of the indoles 2 and 11a and of the alkylating agent 14 are described. A tautomer 12 of 11a is isolated.
Generation and Trapping of Triafulvene
Authors: Weber Andreas , Stämpfli Urs , Neuenschwander Markus
Published: December 2004

Substituted methylidenecyclopropanes 12a–d, being easily available from 1,1‐dibromo‐2‐(phenylthio)‐cyclopropane (9a), are attractive precursors of triafulvene (2‐methylidene‐1‐cyclopropene; 1). Both the sulfoxide 12b and the sulfone 12c react with an excess of alkoxides (t‐BuOK and NaOMe) to give 12e and 12f, respectively, while the sulfinyl group of 12b may be replaced by the PhCH2S substituent in the presence of PhCH2SH/t‐BuOK. These reactions (Scheme 4) may be explained by assuming 1 as a reactive intermediate, although an alternative sequence including carbene 20 (Scheme 6) is not completely ruled out. D‐labelling experiments (Scheme 5) do not give conclusive evidence due to D scrambling, but deprotonation/methylation sequences show that HC(2) of 12a–c is the most acidic proton. Final evidence for 1 results from the reaction of 12d with cyclopentadienide (Scheme 7): the reaction of 1 with cyclopentadiene produces the expected [4 + 2]‐cycloaddition product 23, while some mechanistic insight results from the sequence 12d → 24 → 25.
Cyclization Studies with N‐Mannich bases of 2‐substituted indoles
Authors: Burger Ulrich , Bringhen Alain O.
Published: December 2004

The synthesis of the indoles 7, 15, 16 with a 3‐methoxyphenyl group, attached via an α‐side chain of 1,2,or 3 CH2 units, is reported. These compounds, after appropriate protection at C(3), were transformed into the N‐[(dimethylamino)methyl]indoles 22, 23, and 24, respectively. When treated with AcCl, these N‐Mannich bases gave, in two cases, stable N‐(chloromethyl)indoles 25 and 26. In the presence of SnCl4, ring closure occurred via electrophilic attack of 1‐methylideneindolium ions on the methoxyphenyl group. Formation of seven‐membered rings (→ 27, 28) and eight‐membered rings (→ 29) was found to be a favorable process. Cyclization to six‐membered rings did not occur within this series.
Polynuclear Iron and Rhodium Complexes of 7‐Oxa[2.2.1]hericene (2,3,5,6‐tetramethylidenebicyclo[2.2.1]heptan‐7‐one)
Authors: Rubello Albino , Vogel Pierre
Published: December 2004

μ‐Carbonyl(RhRh)di(η5‐indenyl)[(2R,3S)‐C,2,3,C‐η‐(2,3,4,5‐tetramethylidenebicyclo[2.2.1]heptan‐7‐one)]]‐dirhodium(I)(RhRh) (7) and cis‐μ‐[(2R,3S,5R,6S))‐C,2,3,C‐η:C,5,6,C‐η‐(2,3,5,6‐tetramethylidenebicyclo[2.2.1]heptan‐7‐one)]bis[μ‐carbonyldi(η5‐indenyl)dirhodium(I)(RhRh)] (8) have been prepared. Complex 7 reacts with Fe2(CO)9 in hexane/MeOH and gives cis‐μ‐[(2R,3S,5R,6S] (9), trans‐μ‐[(2R,3S,5S,6R)‐C,2,3,C‐η: C,5,6, C‐η‐(2,3,5,6‐tetramethylidenebicyclo[2.2.1]heptan‐7‐one)‐μ‐carbonyldi(η5‐indenyl)dirhodium(I)(RhRh)‐(tricarbonyliron) (10), and, μ‐carbonyl(RhRh)[(2R,3S)‐C,2,3,C‐η‐(2,3‐dimethyl‐5,6‐dimethylidenebicyclo‐[2.2.1]hept‐2‐en‐7‐one)]di(η5‐indenyl)dirhodium(I)(RhRh) (11). Treatment of 7‐oxa[2.2.1]hericene (4) with Fe2(CO)9 or (cyclooctene)2Fe(CO)3 gave a 1:2 mixture of cis‐μ‐[(2R,3S,5R,6S)‐] (12) and trans‐μ‐[(2R,3S,5S,6R)‐C,2,3,C‐η:C,5,6,C‐η‐(2,3,5,6‐tetramethylidenebicyclo[2.2.1]heptan‐7‐one)]bis(tricarbonyliron)(13).
1,5,7‐Triazabicyclo[4.4.0]dec‐5‐en als Reaktionsmedium: Präparativ ergiebige einstufige Herstellung von Etioporphyrin aus Protoporphyrin
Authors: Kämpfen Ulrich , Eschenmoser Albert
Published: December 2004

1,5,7‐Triazabicyclo[4.4.0]dec‐5‐ene as Reaction Medium: An Efficient One‐Step Formation of Etioporphyrine from Protoporphyrine

Heating the commercially available protoporphyrine (4) in molten 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) at 200° for 4 h under exclusion of O2 produces etioporphyrine (6) in 60–70% yield by bisdecarboxylation and concomitant reduction of the two vinyl groups. Mesoporphyrine (5) is bisdecarboxylated to 6 in over 80% yield under these conditions in TBD as well as in DBU as the reaction medium.
Spectroscopic Studies of Cyclometallated Pd(II) and Pt(II) Complexes: Optical absorption and emission of single crystals of [Pd(thpy)2] and [Pt(thpy)2]
Authors: Schwarz Raimund , Gliemann Günter , Chassot Laurent , Jolliet Philippe , von Zelewsky Alex
Published: December 2004

The polarized optical absorption and emission (spectra, decay times) of single crystals of [Pd(thpy)2] and [Pt(thpy)2] (thpy ≡ C(3′)‐deprotonated form of 2‐(2‐thienyl)pyridine) at temperatures 1.9 K ⩽ T ⩽ 80 K are reported. The emission of [Pt(thpy)2] can be influenced strongly by applied magnetic fields (0 ⩽ H ⩽ 6 T). Depending on the central ions Pd and Pt, the lowest excited electronic states of the single complexes are ligand‐centered (LC) states and metal‐to‐ligand charge transfer (MLCT) states, respectively. This difference leads to distinctly dissimilar properties of the emission of both compounds. The experimental data show that the emission of single crystals of [Pd(thpy)2] and [Pt(thpy)2] at T ⩽ 30 K originates from several types of traps (defect states of symmetry 3B2−stabilized below the exciton band) with LC and MLCT character, respectively. In the Pt compound, the 3B2 is split by spin‐orbit coupling into three states. The states B and A, which determine the emission properties, are separated by Δv ∼ 13 cm−1. Both states can mix under the influence of an applied magnetic field yielding an increase of the emission intensity by a factor of ∼ 1.5 at H = 6 T.
Stereochemical Criteria Providing Unambiguous Experimental Evidence for the intermediacy of ion/molecule complexes in the generation of enolates from gaseous alkoxides. Short communication
Authors: Sülzle Detlev , Schwarz Helmut
Published: December 2004

The epimeric alkoxides 6a and 6b, generated in the gas phase by deprotonation of the stereospecifically deuterated isoborneols 5a and 5b, undergo loss of H2 and HD in a 1:1 ratio. This result, ruling out a concerted one‐step process, establishes the intermediacy of an ion/molecular complex (‘solvated’ hydride ion) in the course of formation of enolates from the alkoxide anions in the gas phase.
Diels‐Alder‐Reaktionen mit 3‐Cyclopropylidenprop‐1‐enyl‐ethyl‐ether als 1,3‐Dien
Authors: Kienzle Frank , Stadlwieser Josef , Mergelsherg Ingrid
Published: December 2004

Diels‐Alder Reactions with 3‐Cyclopropylideneprop‐1‐enyl Ethyl Ether as 1,3‐Diene

The title compound undergoes readily Diels‐Alder reactions with various dienophiles, especially with quinones. The resulting adducts constitute key intermediates in the synthesis of labdane diterpenoids.