bluuebunny/crossref_metadata_2025 huggingface dataset:
17O‐NMR Spectra of Cyclopropenones and Tropone. Oxygen Exchange with Water
Authors: Dahn Hans , Ung‐Truong My‐Ngoc
Published: December 2004

Whereas tropone (2) and a cyclopropanone 5 show rather normal ketone signals in their 17O‐NMR spectra, the two cyclopropenones 1a, and lb exhibit exceptionally high shielding, indicating a structure closer to a O− formula than to a ketone. For comparison, an enolate and several phenolates have been measured. In order to test the ketonic character, the nucleophilic addition of water was determined by the rate of isotopic O‐exchange between ketone and water: 2 exchanged ca. 20 times slower than acetophenone, whereas la reacted very much more slowly.
The Reaction of 1,3‐Butadiene with Ethyl Diazopyruvate. Syntheses of Salicylates and of Nezukone
Authors: Wenkert Ernest , Greenberg Richard S. , Kim Hong‐Seok
Published: December 2004

The Rh‐catalyzed reaction of 1,3‐butadiene with ethyl 3‐diazopyruvate leads, inter alia, to a dihydro‐oxepinecarboxylate whose oxidation and functinal‐group manipulation produce salicylates. Wittig reactions on the acylcyclopropane accompanying the dihydrooxepine yields acrylates whose pyrolyses afford cycloheptadiene‐carboxylates. Oxidation and functional‐group transformation produces the natural tropone, nezukone.
Benzolactone und Benzocarbocyclen durch Ringerweiterung von Benzocycloalkenonen
Authors: Benkert Erwin , Hesse Manfred
Published: December 2004

Benzolactones and Benzocarbocycles by Ring Enlargement of Benzocycloalkenone Derivatives

The Michael adducts 5–8 of benzonitrocycloalkenones 1–4 and acrylaldehyde are converted with (CH3)2 Ti(iPrO)2 or NaCNBH3 to secondary and primary alcohols, 9–12 and 13–16, respectively. These alcohols react under basic conditions to form ring‐enlarged benzonitrolactones and benzooxolactones (Scheme 1). The configuration of the bicyclic intermediates in this enlargement step is discussed. The Michael reactions of benzonitrocycloalkenones with methyl vinyl ketone lead to oxoalkyl‐benzonitrocycloalkenones 35‐‐38. These products rearrange in the presence of t‐BuOK to yield benzonitrocycloalkenones 42, 44, and 46, enlarged by two C‐atoms, or tricyclic hydroxy compounds 39, 41, 43, and 45 (Scheme 4).
Substrate and Positional Selectivity of Free Phenylium Ions toward Arenes in the Gas and Liquid Phases
Authors: Angelini Giancarlo , Keheyan Yeghis , Speranza Maurizio
Published: December 2004

A nuclear technique, based on the spontaneous decay of tritiated precursors that allows the generation of free carbenium ion of exactly the same nature in different environments, has been exploited in a comparative study of aromatic phenylation by free phenylium ions, both in the gas phase at various pressures and in the liquid phase. The differences between the reactivity pattern of the phenylium ion in the two environments can essentially be reduced to significant ion‐neutral electrostatic interaction in the gas phase and, to the much greater efficiency of collisional stabilization, in the condensed phase, allowing a larger fraction of the excited ionic intermediates, from the highly exothermic attack of phenylium ion on the competing arenes, to survive dissociation and isomerization. The mechanism of the major competitive processes promoted by phenylium‐ion attack on arenes, i.e. phenyldehydrogenation and phenyldephenylation, are discussed, together with the substrate and positional selectivity displayed by the nuclear‐decay‐formed phenylium ion toward the selected arenes. The kinetic and mechanistic features of aromatic phenylation, deduced from the present decay experiments, are compared with those of related phenylation reactions carried out in the dilute gas state and in solution.
High‐Yield Synthesis of 20‐, 24‐, and 28‐Membered Macropentolide, ‐hexolide, and ‐heptolide, Respectively, from (R)‐ or (S)‐3‐hydroxybutanoic acid under Yamaguchi's macrolactonization conditions
Authors: Seebach Dieter , Brändli Urs , Schnurrenberger Peter , Przybylski Michael
Published: December 2004

The macrocyclic pentolide 1, hexolide 2, and heptolide 3 constitute ca. 80% of the oligomers formed in ca. 50% yield from enantiomerically pure 3‐hydroxybutanoic acid under Yamaguchi's macrolactonization conditions. The FAB mass spectra of the MH+, M Na+, and MCs+ are reported (Figs. 2, 3, 5, and 6). No cyclic tetramer is detected. The 1H‐NMR spectra of the cyclic oligomers, of the monomer, and of the polymer (PHB) are very similar (Fig. 4). Directed synthesis of the open‐chain dimer and tetramer of 3‐hydroxybutanoic acid and attempted cyclization do not lead to the isolation of the cyclic tetramer.
Note on the Preparation of 1,2‐Diketones from Acetylenes
Authors: Zibuck Regina , Seebach Dieter
Published: December 2004

A mild method for the oxidation of acetylenes to 1,2‐diketones using NaIO4/RuO2 is described. An investigation on the compatibility of various functional groups with this oxidizing agent is reported.
Synthese von Dimethyl‐4a,8a‐methanophthalazin‐1,4‐dicarboxylat und Derivaten
Authors: Neidlein Richard , Tadesse Lema
Published: December 2004

Synthesis of Dimethyl 4a,8a‐Methanophthalazine‐1,4‐dicarboxylate and Derivatives

Diels‐Alder reaction with inversed electron demand of 1H‐cyclopropabenzol 1 with dimethyl 1,2,4,5‐tetrazine‐3,6‐dicarboxylate (2) yields dimethyl‐4a,8a‐methanophthalazine‐1,4‐dicarboxylate (3). The reactions of 3 with nucleophiles are also described.
Hydrogénation de sels de flavylium: formation de composés heptacycliques; structure radiocristallographique du [tétrahydro‐10b,10c,16,16a‐diméthyl‐16,16a‐méthylène‐10b,16‐5aH‐di(benzo[1]pyranno)[4,3‐b:3′,4′,‐c;2,3:2′,3′]‐benz[1]oxépinyl‐5a]‐2‐phénol
Authors: Jolibois Henri , Vebrel Joël , Ouahab Lahcene , Boultif Ahmed , Grandjean Daniel
Published: December 2004

Hydrogenation of Flavylium Salts: Formation of Heptacyclic compounds; X‐Ray Crystal Structure of 2‐[10b,10c,16,16a‐Tetrahydro‐16,16a‐dimethyl‐10b,16‐methylene‐5aH‐di[1]benzopyrano[4,3‐b:3′,4′ ‐c; 2,3:2′,3′][1]benzoxepin‐5a‐yl]phenol

The hydrogenation of flavylium salts 1 either by catalytic reduction or by chemical reduction afforded the unexpected heptacyclic compound 2, the structure of which was determined by X‐ray analysis. The latter was confirmed by 1H‐NMR and mass spectra.
Triaziridine. 9. Mitteilung. Ringöffnungen von Triaziridinen
Authors: Hilpert Hans , Dreiding André S.
Published: December 2004

Triaziridines. Ring Openings of Triaziridines

Eleven triaziridine derivatives were heated at 60° in CDCl3 to obtain information on the tendency towards, resp. the resistance to, ring opening of the N3‐homocycle by thermolysis. Among these triaziridines, there are three which contain, as one of the substituents, a methoxycarbonyl group (ester derivatives 1, 5 and 16), three a methyl group (methyl derivatives 18, 24, and 26), three an H‐atom (14, 27, and 30), and two a negative charge (31 and 32). The other two substituents in each of these four classes of triaziridines are trans‐located i‐Pr groups (1, 18, 27, and 31), cis‐located i‐Pr groups (5, 24, 14, and 32), and a 1,3‐cis‐cyclopentylidene group (16, 26, and 30). As major products these mild thermolyses, we isolated : from the trans‐ester 1 and from the annellated ester derivative 16, the 1‐acyl‐azimines 2 and 17, respectively, from the cis‐ester 5, the 3‐acyl‐triazene 4, from the trans‐methyl derivative 18, the (E)‐diazene 19, and hexamine 21, from the cis‐methyl derivative 24 the 2‐methylazimine 25, both from the trans‐ and cis‐H‐derivatives 27, and 14, respectively, the H‐ triazene 13 and, finally, both from the trans‐and cis‐anion 31 and 32, respectively – after protonation the H‐triazene 13 and – after methylation – the methyl‐triazene 33. The same thermolysis of the annellated methyl and H‐derivatives 26 and 30, respestively, resulted only in decomposition.

These results can be uniformly interpreted with a primary opening of the triaziridine ring by rupture of one of the two types of NN bonds lending to azimines or triazenide anions. Some of the azimines were isolable, namely 2, 17, and 25, and one was spectroscopically observable as an intermediate, namely 11 on the way to the triazene 4. The other azimines are plausible intermediates to the isolated products, namely 15 on the way to 13, and 22 on the way to 19 and 21. The triazenide anion 28 is the evident intermediate on the way to 13 or to 33. The annellated azimines are assumed not be formed from 26 and 30, or then to be be decomposed under the conditions of their formation. We conclude that the triaziridine derivatives 1, 16, and 18 underwent thermal ring opening between N(1) and N(2), while the derivatives 5, 14, 24, 27, 31, and 32 were ruptured between N(2) and N(3); no conclusion was possible on the ring opening of the derivatives 26 and 30.

The predominant formation of the (Z)‐azimine 2 from the trans‐triaziridine 1, and of the (E)‐isomer 3 – among the two azimines – from the cis‐triaziridine 5 suggests a stereospecificity in the triaziridine ring openings. This would, however, not be expected to be observable in the products from the other triaziridines, since both NN bonds of the azimine 25 and of the anion 28 probably rotate rapidly and since the secondary trans formations of the other primary products are not able to retain configurational information.
The Synthesis and Photoisomerization of 5‐Methyl‐5‐Vinyl‐1,3‐Cyclopentadiene
Authors: Burger Ulrich , Pamingle‐Cristoforetti Eliane , Bringhen Alain O.
Published: December 2004

A versatile scheme for the synthesis of geminally disubstituted cyclopentadienes is used to prepare the title compound 4. This remarkably stable vinyl‐cyclopentadiene, distinguished by its Cs symmetry, undergoes exclusively electrocyclic ring closure upon direct π–π* excitation at 254 nm. The epimeric vinyl‐housenes 11 and 12, which, for geometric reasons, are insensitive to the walk rearrangement, are suggested to be the primary photo‐products. One of them, 12, due to its syn‐oriented vinyl group, undergoes spontaneous copy rearrangement to give 2‐methylbicyclo[3.2.1]hepta‐2,6‐diene (13). The other, 11, having an anti‐oriented vinyl group, can only undergo thermal return to the starting material 4. Whereas no leakage to a 1,5‐vinyl migration is discernible for the S1 state of 4, the benzophenone‐sensitized photolysis at 350 nm is shown to be governed by this rearrangement. 1‐Methyl‐5‐vinylcyclopenta‐1,3‐diene (14), the unstable primary product of the sensitized photoreaction, is trapped by 4‐phenyl‐3H‐1,2,4‐triazole‐3,5(4H)‐dione (PTAD).
Ferroelectric Liquid Crystals. Part 2. Chiral phenyl benzoates incorporating a trans‐1,4‐disubstituted cyclohexane ring
Authors: Kelly Stephen M. , Buchecker Richard
Published: December 2004

About forty novel phenyl benzoates also incorporating a trans‐1,4‐disubstituted cyclohexane ring and a chiral centre have been prepared. The dependence of the liquid‐crystal transition temperatures of this new class of compounds on lateral substituents, diverse central linkages, chain lengths, and position of the chiral centre has been studied systematically. The synthesis and liquid‐crystal transition temperatures of these new compounds are described in detail.
Ferroelectric Liquid Crystals. Part 3. Achiral phenyl benzoates incorporating a trans‐4‐pentylcyclohexyl moiety
Authors: Kelly Stephen M. , Buchecker Richard
Published: December 2004

About twenty substituted phenyl benzoates incorporating a trans‐4‐pentylcyclohexyl moiety have been synthesised. The synthesis, liquid‐crystal transition temperatures, and enthalpies of fusion are reported. The effect of variations in chainlength and central linkage on the liquid‐crystal transition temperatures is discussed.
[4+2]‐Cycloadditionen von α,β‐ungesättigten Hydrazonen. Teil 2. Pyridin‐2,3‐dicarboximide aus 1,4‐Dihydropyridin‐Derivaten
Authors: Waldner Adrian
Published: December 2004

[4+2] Cycloaddition of α,β‐Unsaturated Hydrazones to Pyridine‐2,3‐dicarboximides via 1,4‐Dihydropyridine Derivatives

The [4 + 2] cycloaddition of α,β‐unsaturated hydrazones of type 1 (1‐aza‐1,2‐butadienes) with maleimides (e.g. 2b) affords the tetrahydropyridines of type 8. Elimination of dimethylamine to 9 is easily achieved by treatment of 8 with silica gel at elevated temperature. Oxidation of the dihydropyridines 9 leads to highly substituted pyridine‐2,3‐dicarboxylic‐acid dervatives 4.
Dediazoniations of arenediazonium ions. Part 26 Influence of Substituents on the Formation of Benzoic Acids in Reactions of Aryl‐Cation‐Type Intermediates with CO
Authors: Ravenscroft Michael D. , Skrabal Peter , Weiss Bettina , Zollinger Heinrich
Published: December 2004

The N2‐molecule‐aryl‐cation pair formed as the first intermediate in dediazoniations of arenediazonium ions can be trapped with CO in H2O with formation of the corresponding arenecarboxylic acids. This reaction is considered as a model for the reverse of dediazoniation, since CO is isoelectronic with N2. The evaluation of the yields of arenecarboxylic acids formed from substituted benzenediazonium ions using Taft's dual substituent parameter treatment demonstrates that the field reaction constant pF and the resonance reaction constant pR are positive and negative, respectively, as expected for a reaction which corresponds electronically to the addition of N2 to aryl cations.
Synthesis and Structure of Carbonyliron Complexes of Allenecarboxylates and Allenic Lactones
Authors: Trifonov Latchezar S. , Orahovats Alexander S. , Prewo Roland , Heimgratner Heinz
Published: December 2004

On irradiation in the presence of Fe(CO)5, the allenecarboxylates 1 afforded binuclear carbonyliron complexex 6 (Scheme 3), whereas the allenic lactone 7 under similar conditions gave a mixture of one binuclear and two mononuclear carbonyliron complexes (9,8, and 10; Scheme 4). The structure of the complexes has been elucidated by X‐ray crystallography. The structure of the binuclear complex 9 corresponds to that of 6, while 8 has been shown to be a 1,3‐butadiene(tricabonyl)iron complex. The unique structure of the 10 represents a new type of allenic complex. A stepwise formation of the complexes via intermediate allene(tetracarbonyl) iron complexes type 11 and 13 is suggested. Treatment of the binuclear complex 6b with FeCl3 led to the formation of the free ligand and a mixture of mononuclear complexes 13 and 14 (Scheme 5). On heating, the 1,3‐diene complex 8 yielded the free ligand 15, the prouduct of a (1,3) H shift in the allene 7; the complex 10 on the other hand liberates 7 on treatment with ethylenetracarbonitrile (TCNE) (Scheme 6).
Complexation of Cu2+ by Binucleating Macrocycles Containing the N6 Donor Set
Authors: Cruse Richard W. , Kaderli Susan , Spieler Walter , Zuberbühler Andreas D.
Published: December 2004

The hexadentate ligands 1,4,7,12,15,18‐hexaazacyclododecosane ([2]aneN6) and 1,4,7,14,17,20‐hexaazacyclohexacosane ([26]aneN6) both form eight complexes with Cu2+, three of them being binuclear. The corresponding stability constants have been determined potentiometrically, and the electronic absorption spectra have been obtained from spectrophotometric data. Possible interactions of the Cu2+ pairs in the three binuclear complexes have, in addition, been investigated by ESR and and linear ‐sweep voltammetry (LSV). The binuclear complex of [22]aneN6 with one addditional OH group is exceptionally stable, ESR‐silent, and the results of the LSV‐experiments are characteristically different from those of the other binuclear complexes with both ligands. This indicates that [22]aneN6 forms a very stable hydroxo‐bridged binuclear Cu2+ complex Cu2L(OH)3+, whereas in the case of [26]andN6 no bridged Cu2+ pair exists.
Une synthèse générale des tétraazamacrocycles mono‐C‐fonctionnalisés
Authors: Benabdallah Tayeb , Guglielmetti Robert
Published: December 2004

A General Synthesis for Mono‐C‐Functionalized Tetrazamacrocycles

A new synthesis, under usual conditions of concentration, medium, and temperature, of a series of mono‐C‐functionalized tetraazamacrocycles is given. The method may easily be generalized. The new procedure allows the modification of the length of the side‐chain or the size of the cavity by choosing fitted staring materials. The key intermediate has a tosylated linear side‐chain susceptible to be transformed into a large variety of functional groups.
Amide‐Bond Syntheses Catalyzed by Penicillin Acylase
Authors: Pessina Antonio , Lüthi Peter , Luisi Pier Luigi , Prenosil Jiri , Zhang You‐Shang
Published: December 2004

The enzymatic synthesis of amide bonds catalyzed by penicillin acylase is investigated both in H2O solution and in organic solvents containing reverse micelles. The specificity of the reaction is rather high on the side of the acyl component, practically only phenylacetic acid gives sizeable yields. On the contrary, a variety of amino‐acid esters, dipeptides, and tripeptides can be used as amino component, e.g., serine methyl ester, methionine ethyl ester, tyrosine ethyl ester, Gly–Asp, Ala–Tyr, Gly–Tyr–Gly etc. However, Many other amino‐acid residues do not react, and the possible reasons for this are discussed. Yields varyin rang the 10–80%. A. systematic study to optimize yields by varying the solvent composition is presented for one model reaction. The enzyme is also able to couple certain D‐amino‐acid residues (e.g. D‐methionine ethyl ester or Gly‐D‐Asp) though at lower rate. Reverse micelles formed by the cationic surfactant cetyltrimethylammonium bromide (CTAB) in CHCl3/isooctane are used to host penicillin acylase and to perform amide synthesis in which the product is perferentially soluble in the organic solvent mixture. The reaction is studied as a function of pH and certain micellar parameters, e. g. wo (wo = [H2O]/[CTAB]). A new membrane enzyme reactor is utilized to separate the product from the enzyme‐containing micelles. The adavantges and the limits of this approach are discussed.
Mécanisme de solvolyse des cis‐ et trans‐(p‐toluènesulfonates) d'aryl‐2‐cyclopentyle I. Etude de la première étape de la solvolyse: effets isotopiques de l' atone de deutérium en position 2, effets de sel basique et effet spécial de sel
Authors: Ronco G. , Petit J.‐P. , Guyon R. , Villa P.
Published: December 2004

Solvolysis Mechanism of cis ‐ and trans‐2‐Arylcylopentyl p‐Toluenesulfonates. The Step: 1‐Deuterium Isotope Effects, Basic Salt Effects, and Special Salt Effect

We have studied the first step of the solvolysis of cis and trans‐2‐arylcyclopentyl p‐toluenesulfonates in HCOOH, AcOH, and EtOh. All substrates show a high kinetic 1‐deuterium isotope effect (kH/kD(1) >1.15). This fact indicates that first step leads to classical intimate ion‐pair Which dissociates to a solvet‐separated ion‐pair, without participation either of solvent, the 2‐aryl group, or a H‐atom at C(2). The slight influence of added basic ions on reaction rate allows us to exclude any direct solvent attack on the covalent substrate even in the most favorable case, i.e. ethanolysis of 2‐(p‐nitrophenyl)cylopentyl‐p‐toluenesulfonates. Furthermore, solvent‐separated ion pair formation is indicated by the special salt effect induced by LiClO4.
Mécanisme de solvolyse des cis‐ et trans‐(p‐toluénesulfonates) d' aryl‐2‐cyclopentyle III. Etude des étapes ultérieures à I'ionisation lors de lasolvolyse du trans‐ (p‐toluènesulfonate) de phényl‐2‐cyclopentyle
Authors: Ronco G. , Guyon R. , Villa P.
Published: December 2004

Solvolysis Mechanism of cis‐and trans‐2‐Arylcycyclopentyl p‐ Toluenesulfonate. Subsequent Steps in trans‐2‐Phenylcyclopenthyl p‐Toluenesulfonate Solvolysis

The solvolysis of the 1‐deuteriated, 2‐deuteriated, and undeuteriated trans‐2‐phenylcyclopentyl p‐toluenesulfonate in HCOOH, AcOH, and EtOH has studied. We have shown that the classical secondary carbocation arising from substrate ionisation undergoes three concurent processes, namely kc (direct product formation),kip (hydrogenium bridged ion formation as tertiary carbocation or products precursor) and kΔph (phenonium‐ion formation as retained product precursor.) The kΔph process contribution increases with solvent ionising power. The kinetic iotope effect of DC(1) show, that the steps following ionisation have a preponderant effect on the total solvolysis rate.
Photophysical Properties and Photochemical Behaviour of Ruthenium(II) complexes containing the 2,2′‐bipyridine and 4,4′‐diphenyl‐2,2′‐bipyridine ligands
Authors: De Cola Luisa , Barigelletti Franceso , Cook Michael J.
Published: December 2004

The temperature dependence of the emission lifetime of the series of complexes Ru(bpy)n(4,4′‐dpb) (bpy = 2,2′bipyridine, 4,4′‐dpb = 4,4′‐diphenyl‐2,2′‐bipyridine) has been studied in propionitrile/butyronitrile (4:5 v/v) solutions in the range 90–293 K. The obtained photophysical parameters show that the energy separation between the metal‐to‐ligand charge tranfer (3MLCT) emitting level and the photoreactive metal‐centered (3MC) level changes across the series (ΔE = 3960, 4100, 4300, and 4700 cm−1 for Ru(bpy)), Ru(bpy)2(4,4′‐dpb)2+, Ru(bpy)(4,4′‐dpb), and Ru(4,4′‐dpb), respectively, where ΔE is the energy separation between the minimum of the 3MLCT potential curve and 3MLCT – 3MC crossing point. Comparison between spectral and electrochemical data indicated that the changes in ΔE are due to stabilization of the MLCT levels in complexes containing 4,4′‐dpb with respect to Ru(bpy)2+3. The photochemical data for the same complexes (as I− salts) have been obtained in CH2Cl2 in the presence of 0.01M Cl− upon irradiation at 462 nm. The complexes containing 4,4′‐dpb are more photostable than Ru(bpy). Comparison between the data for thermal population of the 3MC photoreactive state and those for photochemistry indicated that the overall photochemical process is governed by (i) a thermal redistribution between the emitting and photoreactive excited states, and (ii) mechanistic factors, likely related to the size of the detaching ligand.
8‐Aza‐7‐deaza‐2′,3′‐dideoxyguanosine: Deoxygenation of its 2′deoxy‐β‐D‐ribofuranoside
Authors: Seela Frank , Driller Hansjüegen
Published: December 2004

The synthesis of 6‐amino‐1‐(2′,3′‐dideoxy‐β‐D‐glycero‐pentofuranosyl)‐1H‐pyrazolo[3,4‐d]pyrimidin‐4(5H)‐one ( =8‐aza‐7‐deaza‐2′,3′‐dideoxyguanosine; 1) from its 2′‐deoxyribofuranoside 5a by a five‐step deoxygenation route is described. The precursor of 5a, 3a, was prepared by solid‐liquid phase‐transfer glyscosylation which gave higher yields (57%) than the liquid‐liquid method. Ammonoloysis of 3b furnished the diamino nucleoside 3c. Compound 1 was less acid sensitive at the N‐glycosydic bond than 2′,3′‐dideoxyguanosine (2).
A novel rearrangement of 2(5H)‐furanones
Authors: Mack Robert A. , DeCory Thomas R. , Georgiev Vassil St.
Published: December 2004

A novel rearrangement of 2(5H)‐furanones is described. When refluxed in aq. Ethanolic solution in the presence of excess KOH, the 2,5‐dihydro‐2‐oxofuran‐3‐carboxamides 6 underwent a novel rearrangement to the corresponding 4,5‐dihydro‐4‐oxo‐2‐(phenylamino)‐3‐furancarboxylic acids 1 in moderate‐to‐excellent yields.
Preparation of 3‐Oxo‐ and 3‐Ethylideneazetidine Derivatives
Authors: Bauman Hans , Duthaler Rudolf O.
Published: December 2004

The preparation of 3‐azetidinones with different N‐substituents and their transformation to 3‐ethylideneazetidines has been studied in relation with a projected synthesis of 3‐ethylideneazetidine‐2‐carboxylic acid (= polyoximic acid; 1). The stable crystalline 3‐azetidinone hydrochloride (18), obtained by hydrogenolysis of the known 1‐(diphenylmethyl)‐3‐azetidenone (4), is described for the first time, From this key intermediate, 3‐oxoazetidine‐derived amides, exemplified by benzamide 12,urethanes (e.g. 17), and ureas (e.g. 20) can be prepared in good yield (Scheme 3). The olefination of 3‐azetidinones with alkylidene(triphenyl)phosphoranes is a perparatively useful process only for derivatives with a pyramidal N‐atom, e.g. the diphenylmethyl derivative 4, and not for the amide 12 or the urethane 17 (Scheme 4). 3‐Alkylidene‐azetidines with an amide N‐atom should, therefore, be prepared by exchange of the N‐substituent after the introduction of the double bond.
4,10a‐(Epidithio)‐4,4a,10,10a‐tetrahydro‐1H‐5‐oxaanthracen‐1‐ones, tetracycles with a novel heterocyclic ring system
Authors: Kolly Sandra , Meier Hansrudolf , Rihs Grety , Winkler Tammo
Published: December 2004

The 4,4′,6,6′‐tetrasubstituted 2,2′‐alkylidene‐bisphenols 1 reacted with sulfur monochloride to give 4,10a‐(epidithio)‐4,4a,10,10a‐tetrahydro‐1H‐5‐oxaanthracen‐1‐ones (3 and 4). The structure of the products were elucidated by a combination of X‐ray crystal‐structure analysis and 1H‐ and 13C‐NMR spectroscopy.
The Reversible Proxibarbal‐Valofan Isomerisation. Part I. Kinetic and thermodynamic studies in aqueous solutions
Authors: Wittekind H. Harald , Testa Bernard , Estreicher Jurek
Published: December 2004

The tautomerisation between proxibarbal (I) and the two diastereoisomers of valofan, IIX and IIY, was investigated in aqueous solutions, and various rate and equilibrium caonstants were calculated by compartmental analysis. The proportion of I at equilibrium was found to increase with pH, and indeed, the two equilibrium constants are linear functions of pH. In contrast, the equilibrium‐concentratio ratio of IIY/IIX was close to 63:37 and remained constant in the pH range investigated. The rate constants were also determined as a function of temperature, allowing calculation of the tehrmolynamic parameters. Under physiological conditions, the difference in free energy favouring I vs. IIX and IIY is 6.7 and 5.4KJ · mol−1, respectively.
Syntheses and tandem Diels‐Alder reactivities of 7,7‐diphenyl‐[2.2.1]hericene (= 7‐(diphenylmethylidene)‐2,3,5,6‐ tetramethylidenebicyclo[2.2.1]heptane) and 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

Syntheses of 7,7‐diphenyl[2.2.1]hericene (4) and 7‐oxa[2.2.1]hericene (5) are presented. Rate constants k1 and k2 of the two successive Diels‐Alder additions of ethylenetetracarbonitrile (TCE) to 4 and to 5 have been evaluated. At 25° in toluene, the rate‐constant ratio k1/k2 = 260 and 21 for 4 and 5, respectively. These results are compared with those reported for the tandem Diels‐Alder reactivity of 2,3,5,6‐tetramethylidenebicyclo[2.2.1]heptane and other derivatives.
The Reaction of 3‐(Dimethylamino)‐2H‐azirines with 2,3‐Pyridinedicarboximide
Authors: Obrech Jean‐Pierre , Schönholzer Peter , Jenny Christain Johannes , Prewo Roland , Heimgartner Heinz
Published: December 2004

Reaction of 2,2‐dialkyl‐3‐(dimethylamino)‐2H‐azirines 1a and 1b with 2,3‐pyridinedicarboximide (4) in MeCN or DMF at room temperature yielded two regioisomeric tricyclic 1:1 adducts, the azacyclols 11/12 and 16/17, respectively (Schemes 3 and 4). The structure of 12 was established by X‐ray crystallography. Methanolysis of 11/12 and 16/17 led to mixtures of methyl [4, 4‐dialkyl‐5‐(dimethylamino)‐4H‐imidazol‐2‐yl] pyridine carboxylates 13/14 and 18/19, respectively. The structure of compound 14 is closely related to that of the powerful herbicide 9 (Scheme 9), i.e. the described reactions offer a new synthetic approach to this class of compounds. A mechanistic interpretation for the formation of regioisomeric 1:1 adducts as well as methyl (imidazol‐2‐yl) pyridine carboxylates is depicted in Scheme 5.
A Synthesis of 1D‐ and 1L‐myo‐Inositol 1,3,4,5,‐Tetraphosphate
Authors: Baudin Gisèle , Glänzer Brigitte I. , Swaminathan Kivalur S. , Vasella Andrea
Published: December 2004

A synthesis of 1D‐ and 1L‐myo‐inositol 1,3,4,5,‐tetraphosphate (1a and 1b resp.) is described. The dibenzylated myo‐inositola 9a and 9b, which, by phosphorylation, gave 1a and 1b, respectively, were prepared via two routes. On the one hand, the racemate 3a/3b, obtained from myo‐inositol, was resolved by its transformation into the diastereoisomeric carbamates 5a and 5b. Benzylation and deprotecton of 5a and 5b gave the enantiomers 9a and 9b, respectively. On the other hand, treatment of the diester 18 with pig liver esterase gave the ester 21a with high enantiomeric excess. Benzylation and deprotection of 21a yielded 9b. The dibenzyl derivative 9a was obtained using the same enzymatic hydrolysis followed by a protection‐deprotection sequence.
Intramolecular Dynamics of Five‐coordinate iron Carbonyl Complexes with olefinic ligands as studied by variable‐pressure 1H‐NMR spectroscopy
Authors: Ioset Jacques , Helm Lothar , Merbach André , Roulet Raymond , Grepioni Fabrizia , Braga Dario
Published: December 2004

Variable‐pressure 1H‐NMR Spectroscopy has been used to study the fluxionality of some five‐coordinated Fe complexes in solution. For [Fe(CO)2 1,3‐cyclooctadiene (PPh3)], the CO site exchange is known (by analogy with [Fe(CO)3(1,3‐cyclooctadiene)]) to be a non‐dissociative process, and an activation volume of ca. 0 cm3.mol−1 was indeed obtained. However, for [Fe(CO2){2,3‐η:O‐σ‐(7,7‐dimethoxybicyclo[2.2.1]hept‐2‐ene)}(PPh3)], the activation volume of +5 cm3 mol−1 suggests that an unprecedented dissociation process is responsible for the CO site exchange. The molecular structure of [Fe(CO)2(1,3‐cyclooctadiene)(PPh3)] was ascertained by single‐crystal X‐ray diffractometry. The crystals are triclinic, space group P1, a = 9.606(3), b = 16.795(2), c = 7.743(8) Å, α = 97.83(4), β = 109.63(4), γ = 83.37(2)°. The structure determination has shown that the complex possesses a tetragonal pyramidal coordination, with the endocyclic CC bond and PPh3 occupying basal sites.
Semicorrin Metal Complexes as Enantioselective Catalysts. Part 1. Synthesis of chiral semicorrin ligands and general concepts
Authors: Fritschi Hugo , Leutenegger Urs , Siegmann Konstantin , Pfaltz Andreas , Keller Walter , Kratky Christoph
Published: December 2004

An efficient synthesis of chiral semicorrin ligands is described (see 6–9, Schemes 2 and 3). Both enantiomers are readily obtained in enantiomerically pure form starting either from D‐or L‐pyroglutamic acid (1). Semicorrins of this type possess several features that make them attractive ligands for enantioselective control of metal‐catalyzed reactions. Their structure is characterized by C2 symmetry, a conformationally rigid ligand system, and two stereogenic centers adjacent to the coordination sphere. In a metal complex, the two substituents at the stereogenic centers shield the metal atom from two opposite directions and, therefore, are expected to have a pronounced effect on the stereochemical course of a reaction occurring in the coordination sphere. The structure of these two substituents can be easily modified in a variety of ways. A series of (semicorrinato)copper(II) complexes (see 10–14, Scheme 4) has been prepared, and in one case (14), the three‐dimensional structure has been determined by X‐ray analysis (Fig. 1).
Semicorrin metal complexes as enantioselective catalysts. Part 2. Enantioselective cyclopropane formation from olefins with diazo compounds catalyzed by chiral (semicorrinato)copper complexes
Authors: Fritschi Hugo , Leutenegger Urs , Pfaltz Andreas
Published: December 2004

Copper complexes of chiral, C2‐symmetric semicorrin ligands were found to be efficient catalysts for the cyclopropane formation from olefins with diazo compounds. In the presence of 1 mode‐% of catalyst, alkyl diazoacetates reacted smoothly with terminal olefins such as styrene, butadiene, and 1‐heptene to give the corresponding optically active cyclopropanecarboxylic‐acid derivatives (Table 1 Scheme 2). With one of the catalysts, enantioselectivities up to 97% ee were obtained (Table 2). Usually, the reactions were carried out using bis(semicorrinato)copper(II) complexes as precatalysts. In order to produce active catalysts, these complexes had to be activated first by heating in the presence of diazoacetate or by treatment with phenylhydrazine. Experiments with (semicorrinato)copper(I) complexes, prepared in situ from copper(I) tert‐butoxide (Scheme 4), suggest that the actual catalyst is a [mono(semicorrinato)]copper(I).
Photoinduced Double Addition of Acetylene to 3‐Oxocyclopent‐1‐ene‐1‐carbonitrile or 3‐oxocyclopent‐1‐enyl acetate leading to 2,3‐dihydro‐1H‐inden‐1‐one and other rearranged products
Authors: Cavazza Marino , Guella Graziano , Pietra Francesco
Published: December 2004

UV Irradiation of 3‐oxocyclopent‐1‐enyl acetate (17) and acetylene in MeCN at 0° gives, besides the product of normal enone‐alkyne [2 + 2] cycloaddition (cis‐4‐oxobicyclo[3.2.0] hept‐6‐en‐1‐yl acetate, 18) and its product of oxa‐di‐π‐methane rearrangement (5‐oxotricyclo[4.1.0.02,7]hept‐2‐yl acetate, 19), unexpected products of further addition of a molar equivalent of acetylene. These are indanone ( = 2,3‐dihydro‐1H‐inden‐1‐one, 16), in 21% yield, cis‐1‐cisoid‐1,2‐cis‐2‐ (20) and cis‐1‐transoid‐1,2‐cis‐2‐7‐oxotricyclo[4.3.0.02,5]non‐3‐en‐1‐yl acetate (21), 4‐oxo‐7‐‘exo’‐vinyltricyclo[3.2.0.02,6]hept‐2‐yl acetate (22), cis‐4‐oxo‐6‐‘endo’‐ (23) and cis‐4‐oxo‐6‐‘exo’‐vinylbicyclo[3.2.0]hept‐1‐yl acetate (24), and cis‐4‐oxo‐7‐‘exo’‐vinylbicyclo[3.2.0]hept‐1‐yl acetate (25). At least in part, indanone must be formed via intermediates 20 and 21. In fact, on heating a 9:1 mixture 20/21, indanone is obtained quantitatively. With 3‐oxocyclopent‐1‐ene‐1‐carbonitrile (15) in place of 17, indanone is formed in lower (8%) yield besides much tars.
Studies on Antifungal Agents. Part 25. 1‐[(3,5‐Bisaryl‐2‐methylisoxazolidin‐3‐yl)methyl]‐1H‐1,2,4‐triazoles
Authors: Bennett Grace A. , Swift Patricia A. , Mullen George B. , Mitchell Jeffrey T. , Allen Stanley D. , Jones Wendy E. , Kinsolving C. Richard , St. Georgiev Vassil
Published: December 2004

The synthesis and antifungal activity of a novel series of 1‐[(3,5‐bisaryl‐2‐methylisoxazolidin‐3‐yl)methyl]‐1H‐1,2,4‐triazoles 6 and 7 (i.e. 8–19) are discussed. The preparation of 8–19 was straightforward and highlighted by a regiospecific 1,3‐dipolar cycloaddition of α‐substituted (E)‐ketonitrones 4 with appropriate atyrene derivatives 5 that led to a cis/trans‐diastereoisomeric mixture of the corresponding triazoles (Scheme). The title compounds were evaluated for in vitro antifungal activity in solid agar cultures against a broad array of yeast and systemic mycoses and dermatophytes. The in vivo activity was determined in an immune‐compromised mouse model of systemic candidiasis. While the in vitro activity was evident throughout the series, it was moderate in potency. However, some of the triazole derivatives demonstrated a potent in vivo activity comparable to that of the standard drug ketoconazole. Analogue 12 (PR 988‐399) emerged as the best overall compound demonstrating potent antifungal activity in both in vitro and in vivo assays.
The Radical Anions of N,N′‐Dicyanoquinone Diimines, a New Class of Electron Acceptors
Authors: Gerson Fabian , Gescheidt Georg , Möckel Reinhart , Aumüller Alexander , Erk Peter , Hünig Siegfried
Published: December 2004

The radical anions of 12 N,N′‐dicyanoquinone diimines, a new class of electron acceptors, hace been characterized by their hyperfine data with the use of ESR and ENDOR spectroscopy. The largest coupling constant (0.30–0.45 mT), due to the two 14N nuclei in the exocyclic positions, gives rise to a conspicuous broadening of the peripheral ESR lines by an incomplete averaging of the hyperfine anisotropy. The most plausible interpretation of the experimental results for the radical anions of N,N′‐dicyano‐ 1,4‐benzoquinone diimine (1) and N,N′‐Dicyano‐9,10‐anthraquinone diimine (9) is in terms of both ‘syn’‐ and ‘anti’‐configurations contributing to the ESR and ENDOR spectra and having equal proton‐ and 14N‐coupling constants. The π‐spin distribution in the radical anions of N,N′‐dicyanoquinone diimines is compared with those in the analogous ions of tetracyanoquinodimethanes and quinones.
Eine neue Synthese von Muscon und Exalton®. Die Enamin‐Route der Ringerweiterungsreaktion
Authors: Bienz Stefan , Hesse Manfred
Published: December 2004

A New Synthesis of Muscone and Exaltone®. The Enamine Approach of Ring‐Enlargement Reaction

Key reaction in the synthesis of the title compounds is the treatment of the aldehydes 6 and 7 (obtained from 1) with a primary amine, e.g. pentylamine, in EtOH at room temperature. After stirring overnight, the products 8 and 9, respectively, are obtained in good yields. Both are enlargement by three ring members and can be transformed to Exalton® (12) and (±)‐muscone, (13), respectively.
Thioalkylation of Meldrum's Acid: Protected alkylidene derivatives of isopropylidene malonate
Authors: Eberle Martin , Lawton Richard G.
Published: December 2004

Thioalkylated Meldrum's acid is easily by treatment of Meldrum's acid with an aldehyde and thiophenol in the presence of catalytical amounts of piperidinium acetate (→1–6, Table 1). The adducts 1–6 are crystalline, stable compounds and they can be caused to react directly with nucleophiles and dienes (see 3→7–12, Scheme 1). The regeneration of the parent olefin is effected thereby by simply dissolving the adduct under neutral or basic conditions. Extension of this method to thiocarboxylic acids allowed the preparation of the corresponding formaldehyde derivatives 13 and 15 (Table 3).
Synthesen von enantiomerenreinen Apoviolaxanthin‐säuren, ‐olen und ‐alen (Persicaxanthin, Sinensiaxanthin und β‐Citraurin‐epoxid) und ihrer furanoiden Umlagerungsprodukte
Authors: Uebelhart Peter , Eugster Conrad Hans
Published: December 2004

Synthesis of Enantiomerically Pure Apoviolaxanthinoic Acids, Apoviolaxanthinols, and Apoviolaxanthinals (Including Persicaxanthin, Sinensiaxanthin, and β‐Citraurin Epoxide) and of their Furanoid Rearrangement Products

Starting from (1′S,2′R,4′S,2E,4E)‐5‐(1′,2′‐epoxy‐4′‐hydroxy‐2′,6′,6′‐trimethylcyclohexy1)‐3‐methy1‐2,4‐pentadienal (3), a recently described synthon [6], a full range of C20‐, C25‐, C27‐, and C30‐polyenic acids, alcohols, and aldehydes and their (8R)‐ and (8S)‐diastereoisomeric furanoid rearrangement products was prepared. The synthetic C25‐alcohols proved to be identical with persicaxanthin (= 12′‐apoviolaxanthin‐12′‐ol) and perisicachromes (= 12′‐apoauroxanthin‐12′‐ols) and the C27‐alcohols analogously with sinensiaxanthin and sinensiachromes. A correlation between the sign of the Cotton effects in the CD spectra of 5,6‐and 5,8‐epoxides and their configuration at C(6) and C(8), respectively, was established.
Anwendungsbreite der reduktiven Kupplung aromatischer Aldimin‐Derivate mit niedervalenten Titan‐Reagenzien zu 1,2‐Diarylethylendiaminen
Authors: Betschart Claudia , Schmidt Beat , Seebach Dieter
Published: December 2004

Scope and Limitations of the Reductive Coupling of Aromatic Aldimine Derivatives with Formation of 1,2‐Diarylethylenediamine Units, Using Low‐Valent Titanium Reagents

Besides the adducts from lithium amides to aromatic aldehydes, iminium salts, animals, and N‐silylimines of aromatic aldehydes are coupled by the black suspension obtained from TiCL4 and Mg turnings in tetrahydrofuran (THF). The 1,2‐diarylethylenediamines with tertiary and primary amino groups thus obtained are formed with no or only moderate diastereoselectivity (products 4a–d (Scheme 2) and 5–e (Scheme 3), respectively); the amine component may contain a strained ring or additional heteroatoms as in azetidin, bis(2‐methoxyethyl)amine, piperazine, morpholine, and thiomorpholine (products 6a–e; Table 1). By an in‐situ procedure, ethylenediamines exclusively trans‐diaryl‐substituted piperazine and perhydro‐1,4‐diazepine derivatives (products 7a–f; Table 2). Enantiomerically pure monocyclic trans,cis‐5‐alkyl‐2,‐3‐diaryl‐piperazines and diazabicyclo[4.3.0]nonanes and ‐[4.4.0]decanes are obtained by employing suitable diamines prepared from the amino acids (S)‐alanine, (S)‐phenylalanine, (S)‐proline and from (S,S)‐ or (R,R)‐cyclohexane‐1,2‐diamine, respectively (products 11a–i, 7e; Table 4). The configuration of all products are derived from the high‐field NMR spectra, some of which are discussed in detail (Figs. 1 and 2, Tables 3 and 5); all new compounds are fully characterized by their physical data. Depending upon the structure of the components employed, the yields of purified products range from as low as 7% to essentially quantitative.
Synthesis und thermisches Verhalten von exo‐3‐Methylidentricyclo[3.2.1.02,4]oct‐6‐en
Authors: Stämpfli Urs , Neuenschwander Markus
Published: December 2004

Synthesis and Thermal Behaviour of exo‐3‐Methylidenetricyclo[3.2.1.02,4]oct‐6‐ene

The title compound 3 has been prepared in 16% yield starting from 8,9,10‐trinorborna‐2,5‐diene. Heating 3 at 140° for 4 h does not give triafulvene and cyclopentadiene by Diels‐Alder cycloreversion, instead the tetracyclic compound 10 has been isolated (81%), which is presumably formed via the diradical 11.
Über den Einfluss des Akzeptor‐Teilchromophors bei Dimethin‐merocyanin‐Farbstoffen auf das Aggregationsverhalten in wässriger Lösung
Authors: Kussler Manfred , Balli Heinz
Published: December 2004

On the Influence of the Acceptor Part of the Chromophor of Dimethinemerocyanine Dyes upon the Aggregation Tendency in Aqueous Solution

A series of novel long‐chain alkyl‐dimethinemerocyanine dyes containing sulfonate groups is synthesized in good yield and their aggregation tendency in H2O and in organic solvent/H2O mixtures investigated. The merocyanine dyes 11 and 15 only exhibit an intense, red‐shifted absorption band due to J‐aggregation in H2O without addition of salt. The influence of cationic and anionic tensides and other compounds as urea, glucose, and polysaccharides upon the J‐aggregation tendency is investigated.
Locoselective [4 + 2] Cycloadditions of Vinylindoles with Inverse Electron Demand: A new access of indolyl‐substituted and annellated pyridazines
Authors: Pindur Ulf , Pfeuffer Ludwig , Kim Myung‐Hwa
Published: December 2004

2‐Vinylindole (1a) and its donor‐ and acceptor‐substituted (E)‐derivatives 1b–e react highly locoselectively with dimethyl 1,2,4,5‐tetrazine‐3,6‐dicarboxylate (3) to form the novel (indol‐2‐yl)‐1,4‐dihydropyridazines 4a and 7 as well as the heterocyclic annellated pyridazines 4b, 5, and 6. The reactions of the structurally related 3‐vinylindoles 2a–e with 3 also gave rise to new indol‐3‐ylpyridazines 8, 9, and 10. The locoselectivities of these Diels‐Alder reactions were controlled mainly by steric effects.
Metal Complexes with Macrocyclic Ligands. Part XXIX.. Structural and kinetic studies of two isomeric Cu2+ complexes with 1,4‐dimethyl‐8‐[2‐(2‐pyridyl)ethyl]‐1,4,8,11‐tetraazacyclotetradecane
Authors: Tschudin Daniel , Riesen Andreas , Kaden Thomas A.
Published: December 2004

The synthesis and complexation properties of 1,4‐dimethyl‐8‐[2‐(2‐pyridyl)ethyl]‐1,4,8,11‐tetraazacyclotetra‐decane (2) are described. This ligand forms with Cu2+ two complexes, one of which has been characterized by X‐ray structure analysis. The structural, spectral, and kinetic studies indicate that the two Cu2+ complexes are isomers with the macrocycle in the trans‐III and trans‐I configuration. The rate of the interconversion of the trans‐I isomer to the thermodynamically more stable trans‐III species is proportional to [OH−]. A mechanism for this reaction is proposed.
Ein neuer Zugang zu 2,6,6‐Trimethylcyclohexa‐2,4‐dienon aus 4‐Oxoisophoron
Authors: Soukup Milan , Lukáč Teodor , Zell Reinhard , Roessler Felix , Steiner Kurt , Widmer Erich
Published: December 2004

A New Access to 2,6,6‐Trimethylcyclohexa‐2,4‐dienone from 4‐Oxoisophorone

2,6,6‐Trimethylcyclohexa‐2,4‐dienone (1), a versatile starting material for the preparation of some carotenoids and several natural products, was efficiently (73% yield) prepared from oxoisophorone 3. After conversion of 3 to the alcohol 4 or the acetate 5, H2O was eliminated (4→1) under acidic distillative conditions, whereas AcOH could be eliminated (5→l) under Pd(O) catalysis.
Structure Determination of New Isomeric Naphtho[2,3‐b]furan‐4,9‐diones from Tabebuia avellanedae by the selective‐INEPT technique
Authors: Wagner Hildebert , Kreher Bernhard , Lotter Hermann , Hamburger Matthias O. , Cordell Geoffrey A.
Published: December 2004

Beside the known naphthoquinones, dehydro‐α‐lapachone (17) and lapachol (20), four new naphtho[2,3‐b]‐furan‐4,9‐diones, i.e. the 2‐acetyl‐5‐hydroxy. 2‐acetyl‐8‐hydroxy. (−)‐5‐hydroxy‐2‐(1′‐hydroxyethyl), and (±)‐8‐hydroxy‐2‐(1′‐hydroxyethyl) derivatives 16, 15, 12, and 13, respectively, and the new compound benzo[b]furan‐6‐carboxaldehyde (8) have been isolated from a CHCl3 extract of the inner stem bark of Tabebuia avellanedae LORENTZ ex GRISEB., together with four known naphthofurandiones, a dihydroisocoumarin derivative, (−)–6‐hydroxymellein, and five benzoic‐acid and three benzaldehyde derivatives which have not been reported previously from this plant. Structure determination of the isomeric 5‐ and 8‐hydroxynaphtho[2,3−b]furan‐4,9‐diones was carried out unambiguously by a combination of selective‐INEPT experiments and X‐ray crystallographic analysis.
Pteridines. Part XLI. Synthesis and properties of 6,7,8‐trimethyl‐4‐thiolumazine
Authors: Hübsch Walter , Pfleiderer Wolfgang
Published: December 2004

The first representative of the 8‐substituted 4‐thiolumazine series has been synthesized. In a sequence of reactions, 4,6‐dichloropyrimidin‐2‐(1H)‐one (1) is first converted into 4‐chloro‐6‐(methylamino)pyrimidin‐2(1H)‐one (6), then the Cl‐atom displaced by the thioxo group (→7) followed by a coupling reaction with 4‐chlorophenyldiazonium chloride to introduce the necessary N‐function into the 5‐position (→ 9; Scheme 1). Reduction of the p‐chlorophenylazo group leads to the 6‐(methlyamino)‐4‐thiouracil‐5‐amine (10) which on condensation with diacetyl gives 6,7,8‐trimethyl‐4‐thiolumazine (8). The physical properties of 8 are compared with the 2‐thio analog and 6,7,8‐trimethyllumazine indicating that 8 possesses the highest acidity and the longest UV absorption.
Diazotisation Mechanism of Heteroaromatic Amines. Diazotisation of 2‐aminothiazole as an equilibrium
Authors: Diener Heinz , Güleç Bilge , Skrabal Peter , Zollinger Heinrich
Published: December 2004

The rate of diazotization of 2‐aminothiazole was measured in 65 to 75% (w/w) aqueous H2SO4. The kinetic solvent isotope effect of the diazotization in 72% D2SO4/D2O was determined (kH/kD = 5.8 ± 0.2). These data are consistent with a mechanism in which the 2‐aminothiazole, protonated at the ring N‐atom, but not at the NH2 group, is attacked by the NO+ ion. The reaction does not go to completion, but to an equilibrium. The equilibrium concentration of the diazonium ion was determined in 30,50,70, and 90% (w/w) H2SO4 at three initial concentration of reagents (0.001,0.01, and 0.1m). The final concentrations of the reagents and the diazonium ion are consistent with a reversible process. This is the first diazotization for which quantitative evidence for equilibration has been found. In the very large range of acidities used (Ho = −1.73 to −9.01), it was not possible to calculate meaningful equilibrium constants that are independent of the acidity.
2,2′‐Bifurylidene‐5,5′‐diones, Coumarins, 3a, 7a‐dihydro‐1H‐inden‐1‐ones, and 5H‐furo[3,2‐b]pyran‐5‐ones from propyne and carbon monoxide
Authors: Rautenstrauch Valentin , Mégard Patrick , Gamper Betty , Bourdin Bernadette , Walther Eric , Bernardinelli Gerald
Published: December 2004

The [Co2 (CO)8]‐catalyzed reaction between propyne and CO in acetone at 110° and 170 bar was re‐investigated. There are five major products: (E)‐3,4′‐dimethyl‐2,2′‐bifurylidene‐5,5′‐dione (4), 3,5,8‐trimethylcoumarin (8), 3a, 7a‐dihydro‐2,4,7,7a‐tetramethyl‐1H‐inden‐1‐one (9), 2,6‐dimethyl‐5H‐furo [3,2, ‐b]‐ pyran‐5‐one (11), and 2,7‐dimethyl‐5H‐furo 3,2‐b‐pyran‐5‐one (12); of these, only one, 4. had previously been recognized. In parallel experiments were obtained 2,6‐dipentyl‐5 H‐furo[3,2‐b]pyran‐5‐one (13), 2,7‐dipentyl–5H‐furo[3,2‐b]pyran‐5‐one (14), 3a, 7a‐dihydro‐2,4,7,7a‐tetrapentyl‐1H‐inden‐1‐one (15). And 3a, 7a‐dihydro‐2,4,6,7a‐tetrapentyl‐1H‐inden‐1‐one (16) from hept‐1‐yne, and two further types of products from two atypical 1‐alkynes: 3,6,9‐tri(tert‐butyl)‐1‐oxaspiro[4.4]nona‐3,6,8‐trien‐2‐one (20) from (tert‐butyl)acetylene and the exo‐dimer 21 of 2,5‐bis(trimethylsilyl)cyclopenta‐2,4‐dien‐1‐one (22) from (trimethylsilyl)acetylene. Compounds 11,12, and 20 were identified by X‐ray analysis.