bluuebunny/crossref_metadata_2025_split huggingface dataset:
Recherches en vue de la synthèse de barbituriques organostannylés, II
Authors: Maire Jean Claude , Van Rietschoten Jurphaas 
Published: December 2004

Abstract(a) The synthesis of 2,4,6‐trioxo‐1, 3‐di‐tributylstannyl‐hexahydropyrimidine is described.(b) Trimethyltin hydride is found to add in a photochemical reaction to the terminal double bond of diethyl allyl malonate and allyl methyl malonate, giving respectively diethyl‐(3‐trimethylstannylpropyl)‐ (1) and diethyl‐(3‐trimethylstannylpropyl) (2) methyl‐malonates.Treated with urea under the usual conditions, (1) and (2) yield organostannyl barbituric acids.
A Photoelectron‐spectroscopic investigation of the Homoconjugative Interaction between π‐ and Walsh‐Orbitals in endo‐ and exo‐Cyclopropano‐norbornene
Authors: Bischof P. , Heilbronner E. , Prinzbach H. , Martin H. D. 
Published: December 2004

AbstractPhotoelectron spectra of endo‐ and exo‐cyclopropano‐norbornene ( = endo‐ and exo‐tricyclo[3.2.1.02.4]octa‐6‐ene) show that a significant homoconjugation exists between the π‐orbital of the double bond and the symmetric Walsh‐es‐orbital of the cyclopropane ring in the exo‐isomer, whereas the interaction is negligeable in the endo‐derivative.
Alkaloide Von Bulbocodium vernum L Inhaltstoffe der Liliaceae‐Wurmbaeoideae. 75. Mitteilung
Authors: Šantavý F. , Sedmera P. , Snatzke G. , Reichstein T. 
Published: December 2004

AbstractFrom whole plants of Bulbocodium vernum L. the flavone luteoline (I) and the alkaloids colchicine (II), N‐formyl‐N‐deacetylcolchicine (III), 3‐demethylcolchicine (V), (+)‐bulbocodine (IX) and (−)‐kreysigine (XI) were isolated in crystals. The presence of 2‐demethylcolchicine (IV), ß‐ (VII) and γ‐lumicolchicine (VIII), demecolcine (VI) and five not identified alkaloids was demonstrated by thin‐layer chromatography. On the basis of ultraviolet, infrared and mass spectra, PMR.‐analysis (Overhauser effect), and circular dichroism, the (6a‐R, 8a‐S)homo‐proaporphine structure IX, with one methoxy group at C‐2, has been assigned to (+)‐bulbocodine. The (6a‐R)‐structure (XI) was deduced for (−)‐kreysigine by comparing its optical rotation and circular dichroism which the values of (−)‐multifloramine (X), the structure of which is known.
Isolierung und Abbau von Sordarin. 1. Mitteilung über Sordarin
Authors: Hauser D. , Sigg H. P. 
Published: December 2004

AbstractSordarin (C27H40O8), an antifungal mould metabolite of Sordaria araneosa, has been degraded to the aglykon sordaricin (C20H28O4) and 6‐desoxy‐4‐O‐methyl‐D‐altrose, a hitherto unknown sugar.
The Structure of the Ferrocenyl‐Methyl Cation. Preliminary communication
Authors: Gleiter Rolf , Seeger Rolf 
Published: December 2004

AbstractUsing a modified Extended Hückel (S. C. C.) procedure the structure of the ferrocenyl‐methyl cation has been calculated. The result is a structure (V) with about equal overlap population between all FeC bonds. The methylene group is bent towards the iron atom and both rings are tilted.
Solvolysis and Isomerization of cis‐ and trans‐1‐Bromo‐1‐(p‐anisyl)‐propene (α‐Bromoanethole) Mesomeric Vinyl Cations, Part V
Authors: Grob C. A. , Nussbaumer R. 
Published: December 2004

AbstractThe influence of a β‐methyl group on the reactivity of two stereoisomeric vinyl bromides has been studied. In 80% ethanol cis‐(8) and trans‐α‐bromoanethole (9) undergo first order reactions leading to p‐methoxypropiophenone (15), 1‐ethoxy‐1‐(p‐anisyl)‐propene (16) and p‐anisylpropyne (12). Solvolysis of the cis isomer 8 is accompanied by isomerization to the more stable trans isomer 9 which is approx. eight times less reactive than 8. Cis‐trans isomerization is also observed in nitrobenzene at 150°.These results are in agreement with the unimolecular substitution‐elimination (SN1−E1) mechanism which competes with cis‐trans isomerization at the ion pair stage.The solvolysis rate of 9 is slightly lower and that of 8 somewhat higher than the rate of α‐bromo‐p‐methoxystyrene (3c). In the absence of other effects a β‐methyl group therefore slightly depresses the ionization rate, presumably by steric hindrance of solvation. These results confirm the negligible polar influence of a β‐methyl substituent on the stability of vinyl cations.
Composés d'addition des halogénures de niobium (V) et de tantale(V): III. Détermination de constantes de stabilité par résonance magnétique nucléaire
Authors: Merbach A. , Bünzli J. C. 
Published: December 2004

AbstractIn view of a systematic study of the Lewis acidity of niobium (V) and tantalum (V) halides, NMR. methods for the determination of stability constants are discussed. In the case of rapid exchange chemical shifts are used to determine the relative amounts of adduct(s) and free base(s) in equilibrium. In the case of slow exchange the relative concentrations of the species are given by the peak areas.
Konfigurative Zusammenhänge in der Muscarinreihe; Chiralität des epi‐, allo‐ und epiallo‐Muscarins, des Muscarons und allo‐Muscarons. Zur biogenese des muscarins 37. Mitteilung über muscarin und verwandte stoffe
Authors: Bollinger H. , Eugster C. H. 
Published: December 2004

AbstractThe chirality of all stereoisomeric muscarines has been determined. (–)‐Muscarine chloride was converted to (+)‐normuscarine, which in turn was oxidized to (+)‐normuscarone. Epimerisation by acid catalysis of the latter gave a mixture of the C(2)‐epimers, namely (+)‐normuscarone and (–)‐allo‐normuscarone. From these were prepared by reduction with LiAlH4 optically active stereoisomeric noralcohols. The natural stereoisomeric muscarines so far isolated are: (+)‐(2S, 3R, 5S)‐muscarine, (–)‐(2S, 3R, 5R)‐allo‐muscarine and (+)‐(2S, 3S, 5S)‐epi‐muscarine. Identical chirality appears only at C(2). This fact has to be taken into consideration for further speculations about the biogenesis of muscarines.Optically active muscarone and normuscarone exhibit a strong Cotton effect at 300 nm, which is interpreted in terms of absolute configuration by analogy to optically active substituted cyclopentanones. Optically active allo‐normuscarone exhibits a very weak Cotton effect only, presumably because of predominant pseudo‐rotation.The relative stability of the stereoisomeric norketones has been determined. Normuscarone (cis‐2,5) is by 0,39 kcal/mol more stable than allo‐normuscarone (trans‐2,5).
Unusual Features in the ESR. Spectra of 1, 6‐Methano[10] annulene Radical Anion. A modified mcconnell equation for non‐planar π‐radicals
Authors: Gerson F. , Müllen K. , Vogel E. 
Published: December 2004

AbstractESR. spectra of the radical anions of 1, 6‐methano[10]annulene (I) and its 2,5,7,10‐tetradeuterio derivative II are reported for a temperature range of over 100°. The abnormally small magnitudes of the α‐proton coupling constants are attributed to the deviation of the tenmembered π‐perimeter from planarity; an extension of the McConnell equation is proposed to achieve agreement between theory and experiment. It is suggested that the marked temperature‐dependence of the ESR. spectra arises from slight changes in geometry which for I⊖ should have a more pronounced effect on the α‐proton coupling constants than for planar π‐radicals.
Steroid Total Synthesis, Part IV; (±)‐13β‐ethyl‐17β‐ethynyl‐17β‐hydroxy‐gon‐4‐en‐3‐one
Authors: Rosenberger M. , Fraher T. P. , Saucy G. 
Published: December 2004

AbstractThe title compound (Norgestrel), a potent progestational agent, has been prepared by a new total synthesis. The scheme is based on earlier work with BCD‐tricyclic intermediates, condensation of 2‐ethyl‐cyclopentane‐1,3‐dione with 2‐[2‐diethylamino‐ethyl]‐6‐[4‐t‐butoxy‐pentyl]‐tetrahydropyran‐2‐ol being the key step. The synthesis features the addition of acetylene to a Δ5(10)‐4‐oxa‐17‐keto intermediate, followed by a novel transformation to the final product.
Eine neuartige Fragmentierung bicyclischer Enoläther Verfahren zur Darstellung macrocyclischer Lactone
Authors: Becker J. , Ohloff G. 
Published: December 2004

AbstractVicinal α‐hydroperoxy‐tetrahydropyranyl ethers annelated to cyclododecane are smoothly converted by homolytic fission in about 75% yield to a mixture of the macrocyclic lactones 3, 4, and 5. Based on this observation, an economically feasible synthesis of Exaltolide1 (>65% yield) has been developed. The mechanism of this new β‐fragmentation reaction is discussed.
Eine neuartige radikalinduzierte intramolekulare Gruppenübertragung. Synthese von 18‐Cyan‐corticosteroiden. Über Steroide, 225. Mitteilung
Authors: Kalvoda J. , Botta L. 
Published: December 2004

AbstractA radical‐induced transfer of an entire functional group in steroid derivatives is described: the photolysis of an 11β‐nitrite function initiates the migration of a nitrile group from the 20‐ to the 18‐position. The reaction was used for the synthesis of new 18‐cyano‐corticoids.
Über tribenzylierte D‐Gluco‐ und D‐Galaktopyranoside. 2. Mitteilung über verätherte Kohlenhydrate
Authors: Stanek J. , Sele A. , Jaques R. , Rossi A. 
Published: December 2004

AbstractThe synthesis of ethyl‐3,4,6‐tri‐O‐benzyl‐D‐glucopyranoside and of ethyl‐3,4,6‐tri‐O‐benzyl‐D‐galactopyranoside is described. These compounds are isomers of ethyl‐3,5,6‐tri‐O‐benzyl‐D‐glucofuranoside, GLYVENOL®, a substance displaying interesting pharmacological actions.
Eine neue Synthese des Antibioticums Pyrrolnitrin
Authors: Gosteli J. 
Published: December 2004

Abstract2‐Methyl‐4‐(2‐nitro‐3‐chloro‐phenyl)‐5‐ethoxycarbonyl‐pyrrole is prepared in six steps from 2‐amino‐3‐chloro‐toluene. As the former compound has been converted into pyrrolnitrin by Nakano et al. [4], the reaction sequence described here constitutes a novel synthesis of the antibiotic.
Hetarylnitrenes V. Reactions of Tetrazolopyrazine Ring Contraction of Nitrenodiazines in Solution. Preliminary communication
Authors: Wentrup Curt 
Published: December 2004

AbstractThermolysis of tetrazolopyrazine (1) in organic solvents gives pyrazinylnitrene (2) which undergoes ring contraction to 1‐cyanoimidazole (3). 7‐Methyl‐5‐methylthio‐tetrazolo[1,5‐c]pyrimidine (4) likewise gives 1‐cyano‐2‐methylthio‐4‐methyl‐imidazole (6). The two tetrazoles also undergo ring contraction to 1‐cyanoimidazoles by gas chromatography, and 1 gives a low yield of 3 by photolysis. Thermolysis of 1 and 4 in cyclohexane gives aminopyrazine (7) and 6‐amino‐4‐methyl‐2‐methylthio‐pyrimidine (8), respectively. Tetrazolo[1,5‐a]pyrimidines (9) give only 2‐aminopyrimidines (10).1‐Cyanoimidazole, formed by thermolysis of 1 in acetic acid, reacts further to give 1‐acetylimidazole, which with more acetic acid gives imidazole and acetic anhydride. An earlier report [2] of ring expansion of pyrazinylnitrene in acetic acid is discredited.In protic deuteriated solvents (D3O, CH3OD), tetrazolopyrazine reacts as an enamine, specifically exchanging HC(6) for deuterium.
Uber Pterinchemie. 41. Mitteilung [1]. Eine neue Synthese von D, L‐Biopterin
Authors: Viscontini M. , Frei W. F. 
Published: December 2004

Abstract– Die Kondensation von D, L‐2,3‐O‐Isopropyliden‐4‐methyl‐erythrulose mit 2,4,5‐Triamino‐6‐hydroxypyrimidin wird beschrieben. Die Luft‐Oxydation des hydrierten Kondensationsproduktes führt zu D, L‐1′,2′‐O‐Isopropyliden‐biopterin ohne Abspaltung der Seitenkette. Durch hydrolytische Abspaltung der Isopropylidengruppe wird in guter Ausbeute reines, isomerenfreies D, L‐Biopterin erhalten.
Intramolekulare Übertragung von elektronischer Anregungsenergie in Spiroverbindungen
Authors: Labhart H. , Pantke E. R. , Seibold K. 
Published: December 2004

AbstractIt is shown that the observation of the degree of polarization of the fluorescence of 9,9′‐spirobifluorene VI and of 2,2′‐diamino‐7,7′‐dinitro‐9,9′‐spirobifluorene VII allows a determination of the rate constant for energy transfer from the initially excited to the unexcited part. The rate constants are of the order of 108 s−1 for VI and 3 · 109 s−1 for VII. The corresponding electronic matrix elements of interaction are evaluated. They are rather due to the Coulomb‐interaction of the transition densities than to spiroconjugation. In VI the coupling vanishes in the equilibrium conformation, vibronic effects must be evoked for explaining its existence.
Aktivierungsanalytische Bestimmung von seltenen Erden in Gesteinsstandards und in Mondproben
Authors: Krähenbühl U. , Rolli H. P. , von Gunten H. R. 
Published: December 2004

AbstractThe content of rare earth elements was analysed in USGS‐standard rocks BCR‐1 and G‐2 and in lunar fines samples from Apollo‐12 using activation analysis techniques.
Kinetics of Oxygen Exchange in the System BrO ‐ H2O (D2O)
Authors: Gamsjäger H. , Grütter A. , Baertschi P. 
Published: December 2004

AbstractThe kinetics of oxygen exchange between water (H2O, D2O) and 18O‐labelled bromate ion has been investigated over the range of 1.7 ≤ pH ≤ 14.3 and 20 ≤ °C ≤ 95. At 60° and ionic strength I ≃ 1.0M (NaNO3), the experimental results were consistent with the rate laws (R in moll−1 s−1):

From the temperature dependence of the rate constants the activation parameters ΔH≠, ΔS≠ and ΔC≠ were derived.In the acid‐catalysed region the form of the rate law and the direction of the solvent isotope effect were the same as previously found, but the numerical values of ΔH≠ and k2H/k2D differ considerably. For the spontaneous and the OH−‐catalysed exchange reactions bimolecular displacement mechanisms are proposed.
Photochemische Reaktionen. 68. Mitteilung. Die Photoisomerisierung von α,β‐ungesättigten γ,δ‐Epoxyketonen: 9α, 10α‐ und 9β, 10β‐Oxido‐3‐oxo‐17β‐acetoxy‐Δ4‐östren
Authors: Bauer D. , Lizuka T. , Schaffner K. , Jeger O. 
Published: December 2004

AbstractIrradiation in the n→π* absorption band of the α,β‐unsaturated γ,δ‐epoxyketone 5 in ethanol at −65° exclusively afforded the rearranged ene‐dione 13, whereas at + 24° under otherwise unchanged reaction conditions or upon triplet sensitization with Michler's ketone and with acetophenone at + 24° essentially identical mixtures of 13 (major product), 14, and 15 were obtained. Selective π→π* excitation of 5 at −78° and + 24° led to similar product patterns. The 9β,10β‐epimeric epoxyketone 7 selectively isomerized to 14 and 15 at + 24° and n → π* or π → π* excitation.Neither the epoxyketones 5 and 7 nor the photoproducts 13–15 were photochemically interconverted. In separate photolyses each of the latter gave the double bond isomers 16, 18, and 19, respectively. Cleavage of 13 to the dienone aldehyde 17 competed with the double bond shift (→ 16) when photolyzed in alcoholic solvents instead of benzene.The selective transformations 5 → 13 (at −65° and n → π* excitation) and 7 → 14+15 are attributed to stereoelectronic factors facilitating the skeletal rearrangements of the diradicals 53 and 55, the likely primary photoproducts resulting from epoxide cleavage in the triplet‐excited compounds 5 and 7, via the transition states 54, 56, and 57. The loss of selectivity in product formation from 5 at higher temperature and n → π* excitation or triplet sensitization is explicable in terms of radical dissociation into 58 and 59 increasingly participating at the secondary thermal transformations of 53. The similar effect of π → π* excitation even at −78° indicates that some of the π,π* singlet energy may become available as thermal activation energy. It is further suggested that the considerably lesser ring strain in 14 and 15, as compared with 13, is responsible that selectivity in product formation from 7 is maintained also at +24° and at π → π* excitation.
Photochemische Cycloadditionen von 3‐Phenyl‐2H‐azirinen mit aktivierten Doppelbindungen. Vorläufige Mitteilung
Authors: Jackson B. , Märky M. , Hansen H.‐J. , Schmid H. 
Published: December 2004

AbstractIrradiation of 2‐methyl‐ (1a), 2,2‐dimethyl‐ (1b) and 2,3‐diphenyl‐2H‐azirine (1c) in the presence of diethyl mesoxalate yields the corresponding 4‐phenyl‐5,5‐diethoxycarbonyl‐3‐ oxazolines 3a–c. Similar cycloadducts are observed (cf. 6) by irradiation of 1b and 1c in the presence of trifluoroacetophenone. When ethyl cyanoformate is used as trapping agent photolysis of 1b or 1c leads to cycloadducts with the carbonyl and nitrile group, respectively which are present in the cyanoformate.
Photochemie in der Vitamin D‐Reihe. I. Kinetik und Quantenausbeuten der Ergosterinbestrahlung bei λ = 253,7 nm
Authors: Pfoertner K. , Weber J. P. 
Published: December 2004

AbstractIrradiation of Δ5,7‐9α, 10β‐steroids in solution with λ = 253,7 nm yielded no Δ5,7‐9β, 10α‐steroids andvice versa. No back reaction from precalciferol2to ergosterol could be detected by kinetic measurements. This leads to the conclusion that with the mercury resonance line only ring opening and 6,7‐cis/transisomerization but no ring closure occurs.
Photochemie in der Vitamin D‐Reihe. II. Die Wellenlängenabhängigkeit der Photoisomerisationen des Präcalciferols
Authors: Pfoertner K. 
Published: December 2004

AbstractIn addition to the known ring opening at shorter wavelengths it was found that ring opening in Δ5,7‐steroids occurs also at λ > 300 nm. Ring closure of the corresponding seco‐ steroids in this region was confirmed. The existence of three rotational isomers with respect to the 5,6‐bond is assumed to be responsible for the observed wavelength dependency of the photoisomerizations of previtamin D. In this case the 5,6‐s‐trans isomer should absorb uv light at shorter wavelengths yielding tachysterol whereas the two 5,6‐rotational isomers with skew conformation should absorb at longer wavelengths yielding lumisterol and ergosterol, respectively.
Thermisches Verhalten von 1,2‐Dipropenylbenzolen
Authors: Heimgartner H. , Hansen H.‐J. , Schmid H. 
Published: December 2004

Abstract1‐cis, 2‐cis‐Dipropenylbenzene (cis, cis‐1) isomerises thermally at 215–235° with 1st order kinetics to give trans, cis‐1 and vice versa. At equilibrium 89% trans, cis‐ and 11% cis, cis‐1 are present. It is shown by thermal rearrangement of cis, cis‐2′, 2″‐d2‐1 that the isomerisation is attributable to aromatic [1, 7a]‐sigmatropic H‐shifts. trans, trans‐1 rearranges thermally at 225–245° to yield 2, 3‐dimethyl‐1, 2‐dihydronaphthalene (2). The formation of 2 can be visualized by disrotatory ring closure followed by an aromatic [1, 5s]‐sigmatropic H‐shift. 2 is also formed when, cis, cis‐ or trans, cis‐1 are heated for 153 h at 225°. Besides 2 a small amount (3%) of 1‐ethyl‐1, 2‐dihydronaphthalene (5) is formed. The rearrangement of trans, trans‐1 and trans, trans‐2′, 2″‐d2‐1 shows a secondary isotope effect kH/kD = 0,90.
The π‐Orbital Sequence in Norbornadiene and Related Hydrocarbons
Authors: Heilbronner E. , Martin H.‐D. 
Published: December 2004

AbstractA method outlined previously [1] is used to show that in norbornadiene (3) the b2(π) orbital lies above a1(π), as predicted by theory. This indicates that in 3 through‐space interaction between the two basis π‐orbitals πa and πb is more important than through‐bond interaction.Analysis of the PE.‐spectra of 8‐isopropylidene‐tricyclo[3.2.1.02,4]‐octane (13) and the corresponding octene (15) confirms that the π‐orbital πc of the exocyclic double bond conjugates more strongly with the symmetric Walsh‐orbital es of the cyclopropano moiety than with the π‐orbital πa of a double bond in the same position.
Reactions of Group 3 Metal Alkyls in the Gas Phase. Part 10: The addition of olefins to the monomeric diisobutylaluminiumhydride
Authors: Egger Kurt W. 
Published: December 2004

AbstractThe relative rate constants for adding ethylene (k1), propylene (k2) and 2‐methyl‐but‐1‐ene (k3) to gaseous diisobutylaluminium hydride produced in situ from AliBu3 have been measured in the temperature range 104–169° in the presence of an excess of equimolar olefin mixtures. The following temperature dependences of the relative rate constants have been obtained:

Two compensating factors determine the rate of addition of olefins to AlH and AlC bonds: (a) the steric effect, reflected in the differences in the preexponential factors and (b) the polar effects, reflected in differences in the activation energies.In the addition of olefins to R2AlH bonds in contrast to R2AlC bonds, the steric effect (a) does not always overrule the opposing energy effect. At temperatures below 125° e.g., isobutene adds slightly faster to HAliBu2, than ethylene. These results are in perfect agreement with expectations based on a reaction mechanism involving a tight asymmetric quadrupolar 4‐centre transition state similar to that postulated earlier for the addition of olefins to AlC bonds.
Untersuchungen der Symmetrieverhältnisse in äquatorial koordinierten 2:1‐Arylazo‐CoIII‐Komplexen mit Hilfe der Protonenresonanz
Authors: Schetty G. , Steiner E. 
Published: December 2004

AbstractThe magnetic equivalence of ligand protons was examined with aid of NMR. spectroscopy for a large number of 1:2 CoIII‐complexes of tridentated azo dyestuffs forming a representative cross section of the whole class of substances. It was established by this investigation that ligands with a moderately polarised azo group have a particular inclination to form asymmetrical complexes in which the protons of the two ligands are not magnetically equivalent. On the other hand, ligands having a non‐polarised or a strongly polarised azo group tend to form symmetrical complexes. In three cases both symmetrical and asymmetrical complexes were isolated. As in previous investigations [1], up to a total of 5 complexes were again observed, which indicates at least two causes governing the symmetry conditions. The phenomena described here could be explained with an alternative coordination of the two azo nitrogen atoms. On the basis of the NMR. results, however, preference is given to an exchange of the azo with the hydrazone form.
Notiz über das Vorkommen von 4′,5‐Dihydroxy‐3,3′,6,7‐tetramethoxyflavon (Chrysosplenetin) in Plectranthus marrubioides HOCHST (Labiatae)
Authors: Hensch M. , Eugster C. H. 
Published: December 2004

AbstractChrysosplenetin (4′, 5‐dihydroxy‐3,3′, 6,7‐tetramethoxyflavon) has been isolated from the leaves of Plectranthus marrubioides HOCHST (Labiatae).
Eine neue 2‐Allylphenol‐Cumaran‐Umlagerung
Authors: Schmid E. , Fráter Gy. , Hansen H.‐J. , Schmid H. 
Published: December 2004

Abstract2‐(1′‐Arylallyl)‐phenols (9, 10, 11, 12, 13, 14, 15, 16) are transformed on heating in N, N‐diethylaniline at 225° into trans‐2‐aryl‐3‐methyl‐coumarans (26, 29, 32, 34, 36, 38, 40, 42) in excellent yields. The corresponding cis‐coumarans are minor products. Similar thermal behaviour is shown by 2‐(1′‐vinylallyl)‐phenols (7, 8) which are thermally converted into trans‐3‐methyl‐2‐vinyl‐coumarans (24, 19) and 5‐methyl‐2,5‐dihydro‐(1‐benzoxepins) (25, 18). The latter compounds are thermally unstable and rearrange to give approximatively 3:1 mixtures of trans‐ and cis‐3‐methyl‐2‐vinyl‐coumarans (24, 19). Reaction mechanisms for these new thermal rearrangements are discussed in schemes 2, 3 and 4.The 2‐(1′‐arylallyl)‐phenols 9, 12 and 14 yield under acidic conditions (HBr/HOAc) the expected 3‐aryl‐2‐methyl‐coumarans 28, 35, 39 along with 2‐aryl‐3‐methyl‐coumarans 26, 34, 38 and 2‐aryl‐2‐methyl‐coumarans 44, 45, 46. The intervention of phenonium ions is discussed for these reactions (cf. scheme 5).When the 2‐(1′‐arylallyl)‐phenols 12 and 14 were irradiated in benzene solution with a mercury high pressure lamp, the main products obtained were 3‐aryl‐2‐methyl‐coumarans 35 and 39 which were formed rapidly. 2‐Aryl‐3‐methyl‐coumarans yield also 3‐aryl‐2‐methyl‐coumarans, when irradiated in benzene solution.
On the Correlation between Photoelectron and Electronic Spectra. Part. II: Experimental indications about the shape of lone pair orbitals
Authors: Haselbach E. , Schmelzer A. 
Published: December 2004

AbstractFor a π‐molecular system containing two symmetry‐equivalent heteroatoms, a qualitative relationship between the difference in the n‐ionization potentials (ΔIP) and the difference between the n → π* excitation energies (ΔΔE) is derived, using semi‐localized orbitals as a basis. The comparison between ΔIP and ΔΔE yields information about the energies and/or the shapes of the two lone pair MO's in the model system. The results provide further insight into ‘through space’ and ‘through bond’ interaction concept introduced by Hoffmann.