bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative Line‐Shape Analysis of Temperature‐ and Concentration‐Dependent 13C‐NMR Spectra of 6Li‐ and 13C‐Labelled Organolithium Compounds. Kinetic and Thermodynamic Data for Exchange Processes in Dibromomethyllithium, (Phenylthio)methyllithium, and Butyllithium
Authors: Heinzer Josef , Oth Jean F. M. , Seebach Dieter 
Published: December 2004

AbstractUsing the ‘permutation of indices’ method proposed by Kaplan and Fraenkel, we could formulate the density‐matrix equations required to fit the temperature‐dependent 13C‐NMR spectra observed with the title compounds. For 6Li13CHBr2 (1) and 6Li13CH2SC6H5 (2) an exchange mechanism is proposed by which monomers interchange C‐ and Li‐atoms via a non‐observed dimeric intermediate; the activation parameters of these intermolecular dynamic processes have been found to be ΔH≠ = 10.2 kcal/mol, ΔS≠ = 13.7 cal/mol·K for 1 and ΔH≠ = 11.1 kcal/mol, ΔS≠ = 20.6 cal/mol·K for 2 ((D8)THF as solvent). In the case of (6Li)butyllithium (3), the observed low‐temperature spectra indicate that dimeric (3b) and tetrameric (3a) species are in dynamic equilibrium interchanging the C3HCH2 groups (and THF molecules) bonded to the 6Li‐atoms. The relative concentrations of the dimer and of the tetramer have been determined by peak integration or by line‐shape fitting; the ‘pseudo’‐ equilibrium constant, defined by K′eq = [3b]2/[3a], was found to be 2.6·10−2 mol/1 (at −88°) and corresponds to ΔGR (−88°) = 2 ΔG°f(3b) – ΔG°f(3a) = 1.34 kcal/mol. The activation parameters of the dynamic process responsible for the exchange were estimated as ΔH≠ = 3.78 kcal/mol and ΔS≠ = −31.3 cal/mol·K. Tentative interpretation of the thermodynamic and kinetic parameters is given.
The Radical Anions and Trianions of 1,8‐Diphenylnaphthalene and of Some of its Derivatives Containing a Cyclophane Substructure
Authors: Gerson Fabian , Heckendorn René , Möckel Reinhart , Vögtle Fritz 
Published: December 2004

AbstractThe radical anions of 1,8‐diphenylnaphthalene (1) and its decadeuterio‐(D10‐1) and dimethyl‐(2) derivatives, as well as those of [2.0.0] (1,4)benzeno(1,8)naphthaleno(1,4)benzenophane (3) and its olefinic analogue (4) have been studied by ESR and ENDOR spectroscopy, At a variance with a previous report, the spin population in \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {2}^{-\kern-4pt {.}} $\end{document} is to a great extent localized in the naphthalene moiety. A similar spin distribution is found for \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {3}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {4}^{-\kern-4pt {.}} $\end{document}. The ground conformations of \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document}‐\documentclass{article}\pagestyle{empty}\begin{document}$ \rm {4}^{-\kern-4pt {.}} $\end{document} are chiral of C2 symmetry. For \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document}, an energy barrier between these conformations and the angle of twist about the bonds linking the naphthalene moiety with the phenyl substituents were estimated as ca. 50 kJ/mol and ca. 45°, respectively. The radical trianions of 1, D10‐1, and 2, have also been characterized by their hyperfine data. In \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{3-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {2}^{3-\kern-4pt {.}} $\end{document}, the bulk of the spin population resides in the two benzene rings so that these radical trianions can be regarded as the radical anions of ‘open‐chain cyclophanes’ with a fused naphthalene π‐system bearing almost two negative charges. The main features of the spin distribution in both \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{-\kern-4pt {.}} $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ \rm {1}^{3-\kern-4pt {.}} $\end{document} are correctly predicted by an HMO model of 1.
The Reaction of 4‐Oxo‐4H‐[1]benzopyran‐3‐carbaldehyde with 1,2‐Benzenediamine. X‐Ray Structure Analysis of the Reaction Product
Authors: Rihs Grety , Sigg Ivo , Hass Georges , Winkler Tammo 
Published: December 2004

AbstractThe reaction product of 4‐oxo‐4H‐[1]benzopyran‐3‐carbaldehyde and 1,2‐benzenediamine is 1,8‐dihydro‐6,13‐bis(2‐hydroxybenzoyl)dibenzo[b,i]‐1,4,8,11‐tetraazacyclotetradeca‐4,6,11,13‐tetraene (1), and its dehydrogenation product is 3‐(2‐benzimidazolyl)‐4H‐[1]benzopyran‐4‐one (2) as shown by X‐ray structure analysis confirming our earlier report.
Isolement et identification de l'acide furfurique, nouvelle depsidone du lichen Pseudevernia furfuracea (L.) Ach
Authors: Gunzinger Jan , Tabacchi Raffaele 
Published: December 2004

Isolation and Identification of Furfuric Acid a New Depsidone from the Lichen Pseudevernia furfuracea (L.) Ach.The structure of furfuric acid, (1), a new depsidone, isolated from the lichen Pseudevernia furfuracea (L.) Ach. has been established as 4‐formyl‐3,8‐dihydroxy‐9‐(2,4‐dihydroxy‐5‐methoxycarbonyl‐3,6‐dimethylbenzyl)‐1,6‐dimethyl‐11‐oxo‐11H‐dibenzo[b,e][1,4]dioxepin‐7‐carboxylic acid by spectral and chemical methods.
Ligand Substitution Reaction of Bis(ethylenediamine)glycinatocobalt(III) Complex with Ethylenediamine Catalyzed by the Photo‐excited Tris(2,2′‐bipyridine)ruthenium(II) Complex
Authors: Ishikawa Masahiko , Okamoto Ken‐ichi , Hidaka Jinsai , Einaga Hisahiko 
Published: December 2004

AbstractSubstitution reaction with ethylenediamine of coordinated glycinate ligand in bis(ethylenediamine)‐glycinatocobalt(III) complex has been studied in the presence of photo‐excited tris(2,2′‐bipyridine)ruthenium(II) complex in alkaline aqueous solution (buffered around pH 12) containing 1.0M chloride ion at 25°C. VIS absorption and CD spectra were used for the racemate and the optically active isomers of the Co(III) complexes, respectively. The reaction was catalyzed by the excited Ru(II) complex to give tris(ethylenediamine)cobalt(III) complex. Mechanism of the ligand‐substitution reaction and role of the excited Ru(II) complex were discussed.
Chirale Synthesebausteine durch Kolbe‐Elektrolyse enantiomerenreiner β‐Hydroxy‐carbonsäurederivate. (R)‐ und (S)‐Methyl‐sowie (R)‐Trifluormethyl‐γ‐butyrolactone und ‐δ‐valerolactone
Authors: Seebach Dieter , Renaud Philippe 
Published: December 2004

Chiral Building Blocks for Syntheses by Kolbe Electrolysis of Enantiomerically Pure β‐Hydroxybutyric‐Acid Derivatives. (R)‐ and (S)‐Methyl‐, and (R)‐Trifluoromethyl‐γ‐butyrolactones, and ‐δ‐valerolactonesThe coupling of chiral, non‐racemic R* groups by Kolbe electrolysis of carboxylic acids R*COOH is used to prepare compounds with a 1.4‐ and 1.5‐distance of the functional groups. The suitably protected β‐hydroxycarboxylic acids (R)‐ or (S)‐3‐hydroxybutyric acid, (R)‐4,4,4‐trifluoro‐3‐hydroxybutyric acid (as acetates; see 1–6), and (S)‐malic acid (as (2S,5S)‐2‐(tert‐butyl)‐5‐oxo‐1,3‐dioxolan‐4‐acetic acid; see 7) are decarboxylatively dimerized or ‘codimerized’ with 2‐methylpropanoic acid, with 4‐(formylamino)butyric acid, and with monomethyl malonate and succinate. The products formed are derivatives of (R,R)‐1,1,1,6,6,6‐hexafluoro‐2,5‐hexanediol (see 8), of (R)‐5,5,5‐trifluoro‐4‐hydroxypentanoic acid (see 9,10), of (R)‐ and (S)‐5‐hydroxyhexanoic acid (see 11) and its trifluoro analogue (see 12, 13), of (S)‐2‐hydroxy‐ and (S,S)‐2,5‐dihydroxyadipic acid (see 23, 20), of (S)‐2‐hydroxy‐4‐methylpentanoic acid (‘OH‐leucine’, see 21), and of (S)‐2‐hydroxy‐6‐aminohexanoic acid (‘OH‐lysine’, see 22). Some of these products are further converted to CH3‐ or CF3‐substituted γ‐ and δ‐lactones of (R)‐ or (S)‐configuration (14, 16–19), or to an enantiomerically pure derivative of (R)‐1‐hydroxy‐2‐oxocyclopentane‐1‐carboxylic acid (see 24). Possible uses of these new chiral building blocks for the synthesis of natural products and their CF3 analogues (brefeldin, sulcatol, zearalenone) are discussed. The olfactory properties of (R)‐ and (S)‐δ‐caprolactone (18) are compared with those of (R)‐6,6,6‐trifluoro‐δ‐caprolactone (19).
5,6,7,8‐Tetrahydro‐4H‐1,2,5‐oxadiazocin‐6‐one durch Ringerweiterung nach Addition eines 3‐Isoxazolidinons mit 3‐Amino‐2H‐azirinen
Authors: Hostettler Bernhard , Obrecht Jean Pierre , Prewo Roland , Bieri Jost H. , Heimgartner Heinz 
Published: December 2004

5,6,7,8‐Tetrahydro‐4H‐1,2,5‐oxadiazocin‐6‐ones, Ring Enlargement Products from a 3‐Isoxazolidinone and 3‐Amino‐2H‐azirines3‐Dimethylamino‐2H‐azirines 1 and 4,4‐dimethyl‐3‐isoxazolidinone (7) undergo already at room temperature a ring enlargement reaction to yield 5,6,7,8‐tetrahydro‐4H‐1,2,5‐oxadiazocines of type 8. The structure of 8a has been confirmed by X‐ray crystallography. The conformation of the eight‐membered ring with a trans‐amide group is of particular interest (Fig. 1 and 2).
Selectivity and Charge Transfer in Photoreactions of α,α,α‐Trifluorotoluene with Olefins
Authors: Mattay Jochen , Runsink Jan , Gersdorf Joachim , Rumbach Thomas , Ly Cuong 
Published: December 2004

AbstractIn photoreactions of α,α,α‐trifluorotoluene with olefins, the mode of reaction strongly depends on the charge transfer between the starting materials. Substitution of an F‐atom is preferred if the electron transfer becomes exergonic, i.e. if ΔG <0 according to the Rehm‐Weller equation. In all other systems of ΔG > 0, the olefins undergo cycloaddition onto the arene ring. In the transition area of ΔG ≈︁ 0 eV, both the electron transfer and the reaction mode can be controlled by varying the solvent polarity. For instance, 1 and 9 mainly form cycloaddition products in dioxane (ΔG = + 0.11 eV), whereas in solvents with ε > 3 (ΔG < 0), substitution is the only observed photoreaction. Moreover, in systems of endergonic electron‐transfer processes, the degree and the direction of charge transfer influence both the regio‐ and the stereochemistry of the cycloaddition.
Anion Coreceptor Molecules. Linear Molecular Recognition in the Selective Binding of Dicarboxylate Substrates by Ditopic Polyammonium Macrocycles
Authors: Hosseini Mir Wais , Lehn Jean‐Marie 
Published: December 2004

AbstractThree macrocyclic hexaamines 1, 2, and 4, and the acyclic tetraamine 5 and hexaamine 6 have been synthesized. The hexaamines 1, 2, and 4 are ditopic coreceptor molecules containing two triamine subunits which may bind anionic substrates when protonated. The stability constants of the complexes between the protonated forms of the macrocyclic polyamines and terminal dicarboxylates −O2C−(CH2)m‐ CO2− as well as amino‐acid and dipeptide dicarboxylates have been determined by pH‐metric measurements. Around neutral pH, 1 and 2 give mainly complexes of the fully protonated species 1·6H+ and 2·6H+, whereas 4 yields predominantly complexes of 4·5H+ and 4·4H+. The stability sequences of the complexes formed indicate preferential binding of the dianionic substrates whose length is compatible with the separation of the triammonium binding subunits in the protonated receptor molecules 1, 2, and 4. This selectivity pattern corresponds to a process of linear molecular recognition based on ditopic binding between the two ammonium subunits of the coreceptor and the terminal carboxylates of the substrate of complementary length. The complexes of the acyclic ligands 5 and 6 are much weaker and much less selective, indicating a marked macrocyclic effect on both stability and selectivity of binding, i.e. on recognition.
Crystal Structures of Chiral Ionophores: Bis(9,9′‐spirobifluorene)‐26‐crown‐4 and ‐32‐crown‐6
Authors: Egli Martin , Dobler Max 
Published: December 2004

AbstractThe X‐ray crystal structures of bis(9,9′‐spirobifluorene)‐26‐crown‐4βbenzene solvate (monoclinic, a = 15.47 Å, b 11.265 Å, c = 15.220 Å, β = 91.54°, space group C2) and bis(9,9′‐spirobifluorene)‐32‐crown‐6·dichloromethane solvate (tetragonal, a = 20.958 Å, c = 11.779 Å, space group P41212) are described. Both compounds act as enantioselective ionophores for α‐aminoalcohols.
Steric Effects on Reaction Rates. Part VIII. The Significance of Front Strain Release in Solvolysis of Bridgehead Derivatives
Authors: Müller Paul , Blanc Jacky , Mareda Jiri 
Published: December 2004

AbstractThe steric requirements of leaving groups for 14 bridgehead derivatives have been examined using MM2 calculations. The strain varies almost monotonously throughout the series upon variation of the leaving group from H to C1, OH, CH3, CH3CH2O, (CH3)3CO, (CH3)3C and no significant trends for differential F‐strain effects are detected expect for the perhydrophenalene derivative 13. The experimental rates of solvolysis of bridgehead derivatives correlate well with the calculated steric energy differences between substrate R‐X and the corresponding carbenium ion R⊕. However, the strain calculations using the more recent force‐fields (MM2) disagree, in part, with those reported in the literature: chloride and p‐toluenesulfonate leaving groups correlate with identical slopes, and the perhydrotriquinacene derivative 10 shows no anomalous behavior. The calculations suggest that F‐strain and C,C‐hyperconjugation should not play any dominant role in bridgehead solvolysis.
Über die thermische, katalytische und photochemische Stickstoff‐Eliminierung des 1‐Diazo‐3‐(1‐methylcyclopenta‐2,4‐dienyl)‐2‐propanons
Authors: Burger Ulrich , Zellweger Dominique 
Published: December 2004

The Thermal, Catalytic, and Photochemical Denitrogenation of 1‐Diazo‐3‐(1‐methylcyclopenta‐2,4‐dienyl)‐2‐propanoneThe synthesis of the title compound 12 is described. This diazoketone, distinguished by its Cs‐symmetry and by a built‐in cisoid diene unit, gives 5‐methyltricyclo[3.3.0.02,8]oct‐6‐ene‐3‐one (13) when subjected to thermal or catalytic denitrogenation with rhodium (II) acetate or copper (II) acetylacetonate. Direct irradiation of 12 at 350 nm causes Wolff rearrangement, whereas the benzophenone‐sensitized photolysis gives again ketone 13. A 1,4‐carbene or carbenoid addition was never observed under the conditions described. The ketone 13 equilibrates thermally or under base catalysis with 1‐methyltricyclo[3.3.0.02,8]oct‐6‐ene‐3‐one (17). The key step of this apparent CH3 migration is shown to be a Cope rearrangement of the corresponding enols (hydroxysemibullvalenes).
The Absolute Configuration of β‐Bisabolol
Authors: Ohloff Günther , Giersch Wolfgang , Näf Regula , Delay François 
Published: December 2004

AbstractFrom bergamot oil (Citrus bergamia RISSO), (−)‐(4S, 8R)‐8‐epi‐α‐bisabolol (2) and (−)‐(4R, 8S)‐4‐epi‐β‐bisabolol (3) were isolated. The absolute configuration of their stereoisomers 4 and 5 was established by an enantioselective synthesis starting from (−)‐(S)‐p‐mentha‐1,8‐dien‐4‐ol.
A Comparative 1H‐ and 13C‐NMR Study of the Dianion and Dication of Biphenylene
Authors: Benken Rainer , Finneiser Klaus , Von Puttkamer Henning , Günther Harald , Eliasson Bertil , Edlund Ulf 
Published: December 2004

AbstractBiphenylene dianion has been prepared by Li reduction of the parent hydrocarbon. It is stable below −30° and was characterized by its 1H‐ and 13C‐NMR spectra. A comparison of these data with those of the dication indicates the existence of ion pairs in the dianion case which are responsible for a different charge distribution. The diamagnetic ring currents of both ions, however, are of comparable magnitude, and both are more diatropic than the parent hydrocarbon. Predictions of the π‐charge‐density effect on 1H chemical shifts are improved by calculations that use the linear and quadratic electric‐field effect equation instead of the simple Spiesecke‐Schneider relation.
Acid‐Catalysed Cyclisation of p‐Mentha‐1,8(9)‐diene‐ and p‐Mentha‐1,8(10)‐diene‐9‐carboxylic Acid. Novel Access to the Bicyclo[3.2.1]octane Skeleton
Authors: Giersch Wolfgang , Brauchli Robert , Thommen Walter , Schulte‐Elte Karl H. 
Published: December 2004

AbstractTreatment of the title compounds with either H3PO4 or BF3 · Et2O affords the bridged tricyclic lactones 3 and 7 as main products (57 and 70% yield, resp.). This is an efficient and novel access to specifically functionalised molecules possesing the bicyclo[3.2.1]octane skeleton. Lactones 4 and 5 and the bicyclic ketone 6 were formed as by‐products (2, 7, and 10% yield, resp.).
Die absolute Konfiguration des Spermin‐Alkaloides Aphelandrin
Authors: Guggisberg Armin , Prewo Roland , Hesse Manfred 
Published: December 2004

The Absolute Configuration of the Spermine Alkaloid AphelandrineThe relative configuration of aphelandrine (1) was established by X‐ray structure determination. The absolute configuration of the centers 11 and 18 was determined earlier by chiroptic measurements. Therefore, structure 1 with the configurations 11S, 17S, and 18S represents the absolute configuration of aphelandrine. In the presence of base, 1 was converted to (11S, 17R, 18R) orantine (2). The 1H‐NMR coupling constants between HC(17) and HC(18) (part of the dihydrofuran ring) are very much dependent on the substituent pattern of the amino N‐atoms N(6) and N(10).
Chinazolincarbonsäuren. XII. Mitteilung. Synthese von [2‐(Ethoxycarbonyl)‐3,4‐dihydro‐4‐oxochinazolin‐3‐yl]‐, [2‐(Ethoxycarbonyl)chinazolin‐4‐yloxy]‐ und (5,6,7,8‐Tetrahydro‐2‐phenylchinazolin‐4‐ylthio)alkansäure‐estern
Authors: Süsse Manfred , Adler Frank , Johne Siegfried 
Published: December 2004

Quinazolinecarboxylic Acids. Synthesis of Alkyl [2‐(Ethoxycarbonyl)‐3,4‐dihydro‐4‐oxoquinazolin‐3‐yl]‐, [2‐(Ethoxycarbonyl)quinazolin‐4‐yloxy]‐ and (5,6,7,8‐Tetrahydro‐2‐phenylquinazolin‐4‐ylthio)alkanoatesThe [(2‐aminobenzoyl)amino]alkanoic acids and their esters 1 showed a different reaction behaviour with diethyl oxalate. Compound 1 (n = 2,3) was converted into the quinazolinylalkanoates 3. o‐Aminohippurate yielded with ethyl (chloroformyl)formate a mixture of the amide 4 and the cyclized quinazolinone 7b. Ethyl 3,4‐dihydro‐4‐oxoquinazoline‐2‐carboxylate (6) reacted with 2‐bromoalkanoates, in the presence of NaH, to the [2‐(ethoxycarbonyl)‐3,4‐dihydro‐4‐oxoquinazolin‐3‐y1]acetates 7 in the case of alkyl bromoacetate, and to the O‐alkylated derivatives 8 with the ethyl 2‐bromopropionate and ‐butyrate. 2‐Aminobenzamide (5) gave with ethyl 3‐(chloroformyl)‐2‐propenoate and methyl 3‐(chloroformyl)propionate the amides 9 or 11, respectively, and not the expected quinazolinones. The cyclized product 12 was obtained from 11 and ethyl bromoacetate. Tetrahydroquinazolin‐4(3H)‐thione 14 was synthesized by the reaction of 13 with NH3, and it was alkylated at the S‐atom with bromoalkanoates to 15. The hydrazide 16 was synthesized from 15b with hydrazine hydrate.
Chemical Synthesis of Oligonucleotides Containing N6‐Methyladenine Residues in the GATC Site
Authors: Guy André , Molko Didier , Wagrez Laurence , Téoule Robert 
Published: December 2004

AbstractTo investigate by NMR the effects of adenine methylation, a set of oligodeoxynucleotides has been synthesized by phosphotriester or phosphoramidite procedures on silica‐gel support. The preparation of fully protected 2′‐deoxy‐N6‐methyladenosine 3′‐phosphate 4 and (2′‐deoxy‐N6‐methyladenosin‐3′‐O‐yl)(methoxy)morpholinophosphine 5 is described. The large‐scale chemical synthesis, purification by HPLC, and characterization by MS of these molecules containing N6‐methyladenine is reported.
1,3‐Dioxanone Derivatives from β‐Hydroxy‐carboxylic Acids and Pivalaldehyde. Versatile Building Blocks for Syntheses of Enantiomerically Pure Compounds. A Chiral Acetoacetic Acid Derivative Preliminary Communication
Authors: Seebach Dieter , Zimmermann Jürg 
Published: December 2004

Abstract(R)‐3‐Hydroxybutyric acid (from the biopolymer PHB) and pivalaldehyde give the crystalline cis ‐ or (R,R)‐2‐(tert‐butyl)‐6‐methyl‐1,3‐dioxan‐4‐one (1a), the enolate of which is stable at low temperature in THF solution and can be alkylated diastereoselectively (→3, 4, 5, and 7). Phenylselenation and subsequent elimination give an enantiomerically pure enol acetal 10 of aceto‐acetic acid. Some reactions of 10 have been carried out, such as Michael addition (→11), alkylation on the CH3 substituent (→13), hydrogenation of the CC bond (→1a) and photochemical cycloaddition (→16). The overall reactions are substitutions on the one stereogenic center of the starting β‐hydroxy acid without racemization and without using a chiral auxiliary.
Comparison of the Complexation of Open‐Chain and Cyclic N2S2 Ligands with Cu+ and Cu2+
Authors: Kaden Thomas A. , Kaderli Susanne , Sager Wiebke , Siegfried‐Hertli Liselotte C. , Zuberbühler Andreas D. 
Published: December 2004

AbstractThe complexation properties of the open‐chain N2S2 ligands 1–4 are described and compared to those of analogous N2S2 macrocycles 5–7. With Cu2+, the open‐chain ligands give complexes with the stoichiometry CuL2+ and CuLOH+, the stabilities and absorption spectra of which have been determined. The ligand field exerted by these ligands is relatively constant and independent of the length of the chain. With Cu+, the species CuLH, CuLH2+, and CuL+ were identified and their stabilities measured. The redox potentials calculated from the equilibrium constants and measured by cyclic voltammetry agree and lie between 250 and 280 mV against SHE. The comparison between open‐chain and cyclic ligands shows that (1) a macrocyclic effect is found for Cu2+ but not for Cu+, (2) the ligand‐field strength is very different for the two types of ligands, and (3) the redox potentials span a larger interval for the macrocyclic than for the open‐chain complexes.
Control of the Diels‐Alder‐Addition Regioselectivity by Remote Olefins. Syntheses and Cycloadditions of 2,3,5‐Trimethylidenebicyclo[2.2.1]heptane and 2,3,5,6,7‐Pentamethylidenebicyclo[2.2.2]octane
Authors: Burnier Gérald , Schwager Luis , Vogel Pierre 
Published: December 2004

AbstractThe syntheses of 2,3,5‐trimethylidenebicyclo[2.2.1]heptane (1) and 2,3,5,6,7‐pentamethylidenebicyclo[2.2.2]‐octane (2) are reported. The Diels‐Alder additions of the diene moieties of these polyenes can be regioselective, probably because of a possible transannular interaction between the homoconjugated methylidene and s‐cis‐buta‐diene groups.
Direct Observation of Acetophenone Enol Formed by Photohydration of Phenylacetylene
Authors: Chiang Yvonne , Kresge A. Jerry , Capponi Marco , Wirz Jakob 
Published: December 2004

AbstractThe photohydration of phenylacetylene yields acetophenone enol as a transient primary product which was detected by flash photolysis. The identification of the transient intermediate rests on a quantitative comparison of its decay kinetics with that of authentic acetophenone enol generated by Norrish type‐II photoelimination from γ‐hydroxybutyrophenone in aqueous HCl and aqueous AcOH buffer solutions.
Triaziridines. Part V. A semiempirical MNDO study of nitrogen inversion and amide rotation in Formyltriaziridines
Authors: Kaneti José , Hoesch Lienhard , Dreiding André S. 
Published: December 2004

AbstractSince we found certain structural features of triaziridine (1) obtained by MNDO calculations to be in qualitative agreement with those derived earlier from ab initio calculations, we used the MNDO method to derive properties of formyltriaziridine (2) and 1‐formyl‐2,3‐diisopropyltriaziridine (3) as models for the preparatively known 2,3‐dialkyl‐triaziridine‐1‐carboxylates 4 and 5. The main results are: (a) The triaziridine N‐atoms with H, alkyl, or formyl as substituents (see 2 and 3) are pyramidal. N(1) carrying the formyl group is flatter than N(2) and N(3) with H or alkyl substitent. Bond lengths and angles at N(2) and N(3) are almost identical with those calculated for the N‐atoms of 1. (b) The MNDO inversion barriers at the H‐substituted N(2) and N(3) of 2 are higher than those at the formyl‐substituted N(1), but similar to the ab initio barriers at the N‐atoms of 1. (c) The MNDO inversion barriers at N(1) of 2 and 3 are 53 to 92 kJ/mol, whereas the rotation barriers around the N(1)–C(4) bond are 7 to 23 kJ/mol; thus, the previously observed dynamic NMR phenomena in trans‐2,3‐diisopropyltriaziridine‐carboxylates (5) can now be assigned to the slowing down of N(1) inversion rather than N(1)–C(4) rotation.