bluuebunny/crossref_metadata_2025 huggingface dataset:
Struktur eines O, N‐Ketenacetals: (1 RS, 8 SR, 10 SR, 4(15)Z)‐4‐äthyliden‐5‐oxa‐3‐azatricyclo [8.4.0.03,8]tetradecan
Authors: Kümin Albin , Maverick Emily , Seiler Paul , Vanier Noel , Damm Lorenz , Hobi Reinhard , Dunitz Jack D. , Eschenmoser Albert
Published: December 2004

Structure of a O,N‐Keteneacetal: (1RS, 8SR, 10SR, 4(15)Z)‐4‐Ethylidene‐5‐oxa‐3‐azatricyclo [8.4.0.03,8]tetradecane

Die C‐Atome der äthylidenseitenkette der Titelverbindung 1 sind als C(15) und C(16) (s. Fig. 1) statt systematisch als C(1′) und C(2′) gekennzeichnet. Verbindung 1 kann auch als kondensiertes heterocyclisches Ringsystem benannt werden: 1‐äthyliden‐perhydro[1,3]oxazixino‐[3,4‐b]isochinolin.

Methods for the preparation of a series of model compounds which were required for stereochemical studies are described: the tricyclic O, N‐keteneacetal 1, the two diastereomeric bicyclic amino acids 7 and 10 (see Scheme 2), and the two diastereomeric conformationally fixed tetrahydro‐1,3‐oxazines (=1,3‐oxazixanes) 9 and 11.

An x‐ray analysis of racemic 1 reveals a quasi‐tetrahedral nitrogen pyramid of the O, N‐ketene acetal grouping, and an almost perfect conformational analogy between the N‐ and C‐centered allylic positions at the double bond.
Durch Bromierung ausgelöste Umlagerung tertiärer Allylalkohole: Der Einfluss eines Fluor‐Substituenten auf Reaktionsgeschwindigkeit und Reaktionsverlauf
Authors: Nagakura Isao , Savary Dang Ngoc‐Huê , Schlosser Manfred
Published: December 2004

Rearrangement of Tertiary Allyl Alcohols Induced by Bromination: The Effect of a Fluorine Substituent on the Rate and the Outcome of the Reaction

The allyl alcohol bearing a methyl and a t‐butyl group at the hydroxylated position was found to undergo a rearrangement when treated with bromine (or N‐bromosuccinimide) in an aqueous medium and to afford a product mixture containing two regioisomeric ketones and one oxirane. Introduction of an additional methyl group or a fluorine atom at the non‐terminal olefinic center led to a more selective discrimination between potential migratory groups. As the result of an exclusive t‐butyl shift only one product, a ketone, was formed in both cases. Whereas the reaction rate was only slightly affected by the additional methyl group, it was substantially decreased by the fluorine atom.
Photochemistry of α, β‐Unsaturated γ, δ‐Epoxyesters I: Singlet versus Triplet Reactivity
Authors: Alder Alex Peter , Wolf Hans Richard , Jeger Oskar
Published: December 2004

On triplet excitation (E)‐2 isomerizes to (Z)‐2 and reacts by cleavage of the C(γ), O‐bond to isomeric δ‐ketoester compounds (3 and 4) and 2,5‐dihydrofuran compounds (5 and 19, s. Scheme 1). ‐ On singulet excitation (E)‐2 gives mainly isomers formed by cleavage of the C(γ), C(δ)‐bond (6–14, s. Scheme 1). However, the products 3–5 of the triplet induced cleavage of the C(γ), O‐bond are obtained in small amounts, too. The conversion of (E)‐2 to an intermediate ketonium‐ylide b (s. Scheme 5) is proven by the isolation of its cyclization product 13 and of the acetals 16 and 17, the products of solvent addition to b. ‐ Excitation (λ = 254 nm) of the enol ether (E/Z)‐6 yields the isomeric α, β‐unsaturated ε‐ketoesters (E/Z)‐8 and 9, which undergo photodeconjugation to give the isomeric γ, δ‐unsaturated ε‐ketoesters (E/Z)‐10. ‐ On treatment with BF3O(C2H5)2 (E)‐2 isomerizes by cleavage of the C(δ), O‐bond to the γ‐ketoester (E)‐20 (s. Scheme 2). Conversion of (Z)‐2 with FeCl3 gives the isomeric furan compound 21 exclusively.
Zur Photocyclisierung von N‐Phenacylformamiden
Authors: Wehrli Hansuli
Published: December 2004

UV. Irradiation of N‐Phenacylformamides

UV. irradiation of suitable N‐phenacylformamides (e.g. 2) leads under transfer of the formyl H‐atom to the corresponding β‐lactams (e.g. 3). Scope and structural limitations of the novel reaction are discussed.
High Asymmetric Induction in Lewis Acid‐Promoted Intramolecular Ene‐Type Reactions: A diastereo‐ and enantioselective synthesis of (+)‐α‐allokainic acid. Preliminary Communication
Authors: Oppolzer Wolfgang , Robbiani Christian , Bättig Kurt
Published: December 2004

The monocyclic amino diacid (+)‐α‐allokainic acid 1 has been prepared enantioselectively from the ester of cis‐β‐chloroacrylic acid and (−)‐8‐phenylmenthol by a series of four synthetic operations in over 15% yield. The crucial step is the intramolecular ‘ene‐type’ reaction of the (Z)‐diene 4 which on treatment with a mild Lewis acid undergoes a highly accelerated, dia‐ and enantiostereoselective cyclization to give the pyrrolidines 6 and 7 in a ratio of 95:5 (Scheme 3). Subsequent ester hydrolysis regenerates the auxiliary chiral alcohol. Similar cyclization of the (E)‐diene 5 furnished a 15:85 mixture of 6 and 7 showing an efficient reversal of the optical induction by variation of the enoate geometry.
Stoffwechselprodukte von Mikroorganismen 205. Mitteilung.. Isolierung und Struktur von Streptazolin
Authors: Drautz Hannelore , Zähner Hans , Kupfer Ernst , Keller‐Schierlein Walter
Published: December 2004

Streptazolin, a lipophilic neutral compound giving a yellow colour reaction with Ehrlich reagent, was isolated from cultures of Streptomyces viridochromogenes, strain Tü‐1678. On the basis of a “chemical screening”. Its structure, 1, was determined by spectroscopic investigations and chemical degradations. Dihydrostreptazolin 3 exhibits limited antimicrobial activities. Pharmacological investigations are in progress.
Synthesis, Characterization, and Biological Properties of Five Enkephalin‐like Pentapeptides Containingp‐Nitrophenylalanine
Authors: Fauchère Jean‐Luc , Schiller Peter W.
Published: December 2004

Five pentapeptides with the amino acid sequenceL‐tyrosyl‐D‐alanyl‐glycyl‐L‐p‐nitrophenylalanyl‐X, wherein X =L‐leucine,L‐leucine amide,L‐methionine amide,L‐1‐adamantylalanine amide, andL‐neopentylglycine amide were prepared by chemical synthesis in solution and characterized chemically and physically. The effect of the incorporation of the unnatural amino acids adamantylalanine and neopentylglycine, ‘fat’‐analogues of leucine and methionine, on the inhibition of electrically evoked contractions of the myenteric plexus‐longitudinal muscle preparation from guinea pig ileum was studied. Their activities relative to the peptides with X = Leu · OH, Leu‐NH2, and Met‐NH2(X = Neo‐NH2is particularly potent) are discussed in terms of hydrophobic and steric factors, and resistance towards enzymic degradation.
Photochemical Reactions. 125th communication [1]. Photochemistry of homoconjugated cyclobutanones. I. Synthesis and photolysis of a Spiro [3.6]deca‐5, 7‐dien‐1‐one
Authors: Lyle Terry A. , Frei Bruno
Published: December 2004

The title compound 4 was prepared in 54% overall yield from eucarvone (5). On triplet sensitization 4 gives two products resulting from a 1,2‐acyl shift (8 and 9), whereas singlet excitation of 4 causes decarbonylation and ketene elimination (4 → 10 and 11).
Enantioselective Generation and Diastereoselective Reactions of Chiral Enolates Derived from α‐Heterosubstituted Carboxylic Acids. Preliminary Communication
Authors: Seebach Dieter , Naef Reto
Published: December 2004

Dioxolanones7and8aand oxazolinones9aderived from pivalaldehyde and lactic acid, mandelic acid, and proline, respectively, furnish chiral enolates of type3by deprotonation with LDA. Reactions of these enolates with alkyl halides, aldehydes, and ketones(→ 8b, 9b, 11–13)are highly diastereoselective. Thus, the overall enantioselective α‐alkylation of chiral, non‐racemic α‐heterosubstituted carboxylic acids(4 → 6)is realized.
Substitution of HMPT by the cyclic urea DMPU as a cosolvent for highly reactive nucleophiles and bases
Authors: Mukhopadhyay Triptikumar , Seebach Dieter
Published: December 2004

The cyclic urea DMPU (N, N′‐dimethyl‐N, N′‐propylene urea = 1,3‐dimethyl‐2‐oxo‐hexahydropyrimidine) is shown to exhibit the same effects HMPT in oxirane‐opening with Li‐acetylide, in a Wittig olefination, in the double deprotonation of nitroalkane, in the Michael addition of Li‐dithiane to cyclohexenone, and in selective generations of certain enolates (Schemes 1–7) DMPU might therefore be as safe substitute of the carcinogenic HMPT as a cosolvent with unique properties in diverse type of reaction.
Metal complexes with macrocyclic ligands. XVI. Spectrophotometric and thermodynamic studies of solvents and unidentate ligands interaction with the pentacoordinate Co2+‐, Ni2+‐ and Cu2+‐complexes of 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane
Authors: Micheloni Mauro , Paoletti Piero , Bürki Stephan , Kaden Thomas A.
Published: December 2004

The interaction of solvents and of unidentate ligands such as N, SCN−, OCN− and OH− with the Co2+‐, Ni2+ and Cu2+‐complexes of 1,4,8,11‐tetramethyl‐1,4,8,11‐tetraazacyclotetradecane (TMC) have been studied by Spectrophotometric and calorimetric techniques. The spectra in different solvents (Table 2) show that the Ni2+‐ and probably also the Cu2+‐complex with TMC exist as square planar or pentacoordinate species or as a mixture of both, depending on the donor properties of the solvent. The [Co(TMC)]2+‐complex is pentacoordinate in all the solvents studied.

Ternary complexes [M(TMC)X]n+ are also formed by the unidentate ligands X = N, OCN−, OH−, F− and NH3 and their stability constants have been determined. Interesting is the high selectivity of [Ni(TMC)]2+ towards the addition of a further donor (Table 3). Only small ligands such as those listed above form stable adducts, whereas the larger ones such as imidazole or pyridine do not. This is a consequence of the special structure of the complex and of the trans‐I‐(RSRS)‐ conformation of the ligand in these complexes. Since the four methyl groups are all on the side of the macrocycle to which the additional unidentate ligand binds, steric interaction between the four methyl groups and the larger ligands prevents the formation of the adducts.

The calorimetric measurements show that the stability of the complexes [M(TMC)X]n+ is due to both an enthalpic and entropic contribution which differ in their magnitude (Table 4). This indicates that several antagonistic factors are important in determining the overall stability.
Copper(I)‐ and Copper(II)‐catalyzed Diels‐Alder Additions of α‐Substituted Acrylonitrile to Furan. The Synthesis of 7‐Oxa‐bicyclo[2.2.1]hept‐5‐en‐2‐one
Authors: Vieira Eric , Vogel Pierre
Published: December 2004

The difficult Diels‐Alder additions of α‐acetoxy‐ and α‐chloroacrylonitrile to furan can be run at 20–35° and atmospheric pressure in the presence of CuCl. Cu(BF4) · 6 H2O, Cu(OOCCH3)2 · H2O or cupric tartrate · 3H2O. Under kinetic control, the exo‐carbonitrile adducts 2 and 8, respectively, are favoured. Saponification of the 2endo‐acetoxy‐7‐oxabicyclo[2.2.1]hept‐5‐ene‐2exo‐carbonitrile (2) furnished the 7‐oxabicyclo[2.2.1]hept‐5‐en‐2‐one (4). Basic hydrolysis of the adducts (8 + 9) of α‐chloroacrylonitrile to furan and its 5exo, 6exo‐isopropylidenedioxy derivatives did not give the corresponding ketones, the carboxamides 14 + 15 and 16 + 17, respectively, were isolated.
13C‐NMR.‐Spektren von 3H‐Benz[cd]azulen‐3‐onen
Authors: Neidlein Richard , Kramer Walter , Schcutzow Dieter
Published: December 2004

13C‐NMR. Spectra of 3H‐benz[cd]azulenc‐3‐ones

13C‐NMR. Spectra of 7,9‐dimethyl‐3H‐benz[cd]azulenc‐3‐one (2) and 7,9‐dimethyl‐4,5‐dihydro‐3H‐benz[cd]azulene‐3‐one (7) in CDCl3 and CF3CO2D are reported. The assignment of signals was achieved with the aid of selective proton decoupling, non‐decoupled spectra and comparison with spectra of simple azulene‐derivatives. The major localization of positive charge in the cationic 3‐hydroxybenz‐[cd]azulenium system was found in the six‐ and seven‐membered ring, which suggests in accordance with calculated π‐electron densities the structure of a benztropylium ion rather than a bridged azulenium ion.
The Low‐Temperature UV./VIS. Absorption Spectrum of [18]Annulene
Authors: Baumann Harold , Oth Jean F. M.
Published: December 2004

The UV./VIS. absorption spectrum of [18]annulene has been remeasured in 3‐rnethylpentane at room and at liquid nitrogen (glass) temperature and interpreted by the CNDO/S‐CI‐method. The confrontation of the experimental electronic transitions with the CNDO/S‐CI‐calculated ones favors a structure with D6h‐symmetry, i.e, a structure with delocalized π‐bonds.
The Photooxygenation of Heptamethyl Coα, Coβ‐Dicyanocobyrinate
Authors: Kräutler Bernhard
Published: December 2004

Irradiation with visible light of an oxygen‐saturated methanolic solution of heptamethyl Coα, Coβ‐dicyanocobyrinate and of the sensitizer methylene blue causes the efficient photooxygenation of this vitamin B12 derivative. Use of CD3OD instead of CH3OH strongly accelerates the reaction. This solvent H/D‐isotope effect is consistent with a mechanism involving ‘singlet oxygen’ and is exploited preparatively. Two photooxygenation products can be isolated from such preparative experiments. One of these, isolated in 47% yield, has NMR.‐spectral characteristics identical with those of Inhoffen's heptamethyl Coα,Coβ‐dicyano‐5,6‐dioxo‐5,6‐secocobyrinate (2a). To the other photoproduct, isolated in 25% yield, the structure of the unknown isomeric heptamethyl Coα, Coβ‐dicyano‐14,15‐dioxo‐14, 15‐secocobyrinate (3a) is assigned.
The Light‐Induced Oxygenation of the B‐Didehydrocorrinoid Vitamin‐B12 Derivative ‘Pyrocobester’
Authors: Kräutler Bernhard , Stepánek René , Holze Gerhard
Published: December 2004

The didehydrocorrinoid derivative of vitamin B12, ‘pyrocobester’ 1 (hexamethyl Coα, Cob̃‐dicyano‐7‐de (carboxymethyl)‐7,8‐didehydrocobyrinate), is oxygenated in the presence of visible light and molecular oxygen to give the previously unknown ‘5,6‐dioxosecopyrocobester’ 3 (hexamethyl Coα, Cob̃‐dicyano‐5,6‐dioxo‐7‐de(carboxymethyl)‐7,8‐didehydro‐5,6‐secocobyrinate) under regioselective cleavage of the macrocycle at the 5,6‐position. Efficiency and yield of this reaction involving ‘singlet oxygen’ depend on the solvent used: with CCl4 a 96% yield of 3 is obtained.
Synthesis of Concentrated 18O‐Labelled Hydrogen Peroxide and of 2H‐, 13C‐ and 18O‐Labelled Peroxyformic Acid
Authors: Grassi Guido , Oldani Markus , Bauder Alfred
Published: December 2004

A method is described for the preparation of concentrated solutions (50–70%) of 18O‐labelled H2O2 in water. All singly 2H‐, 13C‐ and 18O‐labelled species of peroxyformic acid have been synthesized by the reaction of appropriately labelled formic acid and H2O2.
Synthese von Glycerylätherphosphatiden 2. Mitteilung Herstellung von 2‐O‐Acetyl‐1‐O‐[(Z)‐9‐octadecenyl] ‐sn‐glyceryl‐3‐phosphorylcholin («Oleyl‐PAF»), des Enantiomeren sowie einiger analoger, ungesättigter Verbindungen
Authors: Hirth Georges , Saroka Hervé , Bannwarth Wilhelm , Barner Richard
Published: December 2004

Synthesis of Glyceryletherphosphatides, 2nd Communication. Preparation of 2‐O‐Acetyl‐1‐O‐[(Z)‐9‐octadecenyl]‐sn ‐glyceryl‐3‐phosphorylcholin (‘Oleyl‐PAF’), of its Enantiomer and Some Analogous, Unsaturated Compounds

Syntheses of the unsaturated glyceroletherphospholipid 1a as an olefin‐analog of ‘Platelet Activating Factor’ (PAF) are described together with the methods for the preparation of the enantiomer 1′a, the corresponding ‘lyso compounds’ 1b and 1′b and their positional isomers 21a, 21′a, 26, 26′, 25, 25′ obtained on formally exchanging the attachment site of the functional groups at the glycerol moiety. Structural assignments and optical purity of the compounds are confirmed.
Metal complexes with macrocyclic ligands. Part XIX. Synthesis and Cu2+‐complexes of a series of 12‐, 14‐ and 16‐membered cis‐ and trans‐N2S2‐macrocycles
Authors: Siegfried Liselotte , Kaden Thomas A.
Published: December 2004

A series of 12‐, 14‐, and 16‐membered N2S2‐macrocycles (9–11 and 19–21) with cis and trans‐arrangement of the heteroatoms have been synthesized by high‐dilution cyclization and subsequent reduction of the amides with B2H6. With these ligands the corresponding Cu2+‐complexes were prepared and their UV/VIS spectra, their electrochemistry and their EPR properties have been studied. Generally three absorption bands at 270–320 nm, 330–370 nm and 530–620 nm can be observed in aqueous solution and these have been assigned to the N→Cu2+ and S→Cu2+ charge‐transfer bands and to the d‐d* transition, respectively. The cyclic voltammetry in CH3CN shows in all cases a reversible or quasi‐reversible Cu2+/Cu+‐transition at potentials of 10–480 mV against SHE. The values of g‖ and A‖ obtained from EPR spectra indicate that the geometry of the Cu2+‐complex of the 14‐membered cis‐N2S2‐macrocycle is less distorted than that of the other complexes.
The Halide‐promoted fragmentation of 1‐chloro‐1‐fluoro‐2‐(a‐silylakyl))cyclopropanes: A new entry to fluorodienes
Authors: Schlosser Manfred , Dahan Rahel , Cottens Sylvain
Published: December 2004

When heated in the presence of tetrabutylammonium fluoride or chloride, 1‐chloro‐1‐fluoro‐2‐(trimethylsilyl)methyl‐cyclopropanes (1, 2 and 3) undergo smooth ring‐opening fragmentation to afford 2‐fluoro‐butadienes ((4, 5 and 6 resp.) with high yields. Despite unfavorable geometries, the reaction is concerted and the inversion mode of rotation dominates over the retention mode by a factor roughly 100.
Preparation and Properties of Bis[μ‐S‐(2‐tiolatoethyl)‐diphenylphosphine][(2‐thiolatoethyl)diphenyl‐phosphine]dinickel(+1) Ion, a Novel Unsymmetrical Thiolate‐bridged complex
Authors: Pfeiffer Ernst , Pasquier Maurice L. , Marty Werner
Published: December 2004

The title cation ( = Ni2L) is formed in a variety of reactions (Schemes 1 and 2) in systems containing Ni2+ and (2‐thiolatoethyl)‐diphenylphosphine (= L−) in the absence of coordinating anions at Ni2+/L− ratios > 0.5 in apolar or moderately polar media. Solid [Ni2L3]CIO4 and [Ni2L3]BPh4 have been isolated. Job's plots confirm the Ni2L‐ stoichiometry in solution. 31P‐NMR data are consistent with ≥ 97% Ni2L (vs. ⩽ 3% of hypothetical Ni3L) at equilibrium and support the suggested configuration (Fig. 2). The equilibrium between NiL2 + NiL2Br2 and Ni2L + Br− varies with the solvent composition in CH23Cl2/EtOH mixtures. The rate of formation of Ni2L2Br2 from Ni2L and bromide (in high excess) in CH2Cl2 is first‐order in [Ni2L]tot but depends on the ratio [Bu4NBr]tot/[Ni2L3 · ClO4]tot, even at a high excess of bromide. This is interpreted by efficient competition in ion‐aggregate formation between the small perchlorate concentration introduced as the counterion of Ni2L, and the large excess of bromide.
Zum Mechanismus der Aziridinsynthese aus 2‐Azidoalkoholen und Triphenylphosphin
Authors: Pöchlauer Peter , Müller Ernst Peter , Peringer Paul
Published: December 2004

On the Mechanism of the Aziridine Synthesis from 2‐Azido‐alcohols and Triphenylphosphine

The reaction of selected 2‐azido‐alcohols, their pivalates, and methanesulfonates with triphenylphosphine was investigated. It is shown that the formation of aziridines from 2‐azido‐alcohols proceeds via 1,3,2λ5oxazaphospholidines. Furthermore, the first synthesis of the unsubstituted acenaphtene‐1,2‐imine is described.
Preparation by yeast reduction and determination of the sense of chirality of enantiomerically pure ethyl (−)‐4,4,4‐trichloro‐3‐hydroxy‐ and (+)‐4,4,4‐trifluoro‐3‐hydroxybutanoate
Authors: Seebach Dieter , Renaud Philippe , Schweizer W. Bernd , Züger Max F. , Brienne Marie‐Josèphe
Published: December 2004

Reduction of ethyl 4,4,4‐trichloro‐ and 4,4,4‐trifluoro‐3‐oxobutanoate by fermenting baker's yeast (Saccharomyces cerevisiae) on a preparative scale (20–50 g in ca. 3 1 of H2O) gave 70–80% yields of the trichloro‐ [(−)‐(S)‐1a] and trifluoro‐hydroxyesters [(+)‐(R)2a] of ca. 85 and 45% ee, respectively. Both, (−)‐1a and (+)‐2a could be obtained in > 98% ee by subsequent crystallization (of(−)‐1, (+)‐2a or the 3,5‐dinitrobenzoate (+)‐2b. The absolute configuration of both hydroxyesters was determined (a) by chemical correlation ((−)‐1a), (b) from the melting diagrams and mixed melting points (differential‐scanning calorimetry Fig. 1) of the dinitrobenzoates of the CF3‐derivative (+)‐2a and its CH3‐analogue 8, and c) by X‐ray analysis of the ester 2f from (+)‐2a and (−)‐camphanoyl chloride (Fig. 2 and 3).
Addition von Dimethylketen an 6‐heterosubstituierte Fulvene. Synthese von (±)‐Filifolon
Authors: Stadler Heinz , Rey Max , Dreiding André S.
Published: December 2004

Addition of Dimethylketene to 6‐Heterosubstituted Fulvenes. Synthesis of (±)‐Filifolone

[2 + 2]Cycloaddition of dimethylketene to 6‐ethoxy‐ (8) and 6,6‐(tetramethylenedithio)fulvene (9) gave the 4‐alkylidenebicyclo[3.2.0]heptenones 11 and 12, respectively. Under the same conditions, 6‐(dimethylamino)fulvene (7) was acylated to yield the push‐pull fulvene 10. Raney‐Ni reduction converted the adduct 12 into the monoterpene (±)‐filifolone ((±)‐1, 52%) and minor amounts of the four related ketones 14‐17. Cycloaddition of a second dimethylketene to the primary cycloadduct 11a yielded the cis, transoid, cis‐tricyclic diketone 13.
Synthesis of aristoteline‐type alkaloids. Part II. The structure of neohobartine, a side product of the hobartine‐aristoteline transformation
Authors: Borschberg Hans‐Jürg
Published: December 2004

The structure of neohobartine (3), a side product of the acid‐catalyzed conversion of (−)‐hobartine (1) into (+)‐aristoteline (2), has been elucidated by spectroscopic methods. Possible mechanistic pathways leading to its 1‐azaaadamantane skeleton are discussed.
Reversed Stereochemical Course of the Michael Addition of Cyclohexanone to β‐Nitrostyrenes by Using 1‐(Trimethylsiloxy)cyclohexene/Dichloro(diisopropoxy)titanium. Preliminary Communication
Authors: Seebach Dieter , Brook Michael A.
Published: December 2004

Induced by a stoichiometric excess of dichloro(diisopropoxy)titanium, 1‐(trimethylsiloxy)cyclohexene and p‐substituted β‐nitrostyrenes (Y = H,CH3,CH3O,CN) combine in CH2Cl2 solution at −90° preferentially with relative topicity ul – opposite to the corresponding reaction of enolates or enamines. The primary products are the bicyclic nitronates 3–5 which can be separated, and which are cleaved by KF in MeOH to give the aryl(nitroethyl)‐substituted cyclohexanones 1 and 2 (Tables 1 and 2, two typical procedures are given). The major products (2:1 to 4:1) are the hitherto not readily available diastereoisomers 2 of l‐configuration. Instead of being solvolyzed, the bicyclic nitronate 5 can be used for nitroaldol additions (→6) and for [3 + 2]‐dipolar cycloadditions (→7), diastereoselectively furnishing products with 4 asymmetric C‐atoms (not counting acetal centers). The Michael addition described here is yet another example of an ul‐combination of trigonal centers induced by Lewis acids, overriding the influence of the configuration of the donor component.
Gas‐Phase Basicities of Open‐Chain and Cyclic Diols from Dissociations of Ammonium Adducts, Protonated Mixed Dimers and ICR Experiments. Structural and Stereochemical Effects
Authors: Guenat Christian , Houriet Raymond , Stahl Daniel , Winkler Johann
Published: December 2004

The gas‐phase basicity (GB) of open‐chain and cyclic diols and triols has been determined by the method of dissociation of proton‐bound adducts using 1,4‐butanediol and cis‐ and trans‐1,3‐cyclohexanediol as reference compounds. The GB and proton affinity (PA) of the two cyclic reference diols have been obtained in ion‐cyclotron‐resonance experiments. The unimolecular and the collision‐activated dissociations of the ammonium adducts of the polyols allow a ranking of their GB and PA values which reflects the various structural and stereochemical effects. The possibility of internal H‐bonding between the two OH groups leads to a strong increase of the PA values. The incremental effect of chain length on the PA of open‐chain diols is evidenced, as well as the detailed influence of the configuration and conformation for cyclopentane‐ and cyclohexanediols, and ‐triols. These experiments also emphasized the predominant role of doubly H‐bound ammonium/diol chelate conformations as opposed to singly proton‐bound species.
Site Selectivity in the Gas‐Phase Ionic Phenylation of Alcohols and Alkyl Chlorides
Authors: Keheyan Yeghis , Speranza Maurizio
Published: December 2004

Free, unsolvated phenylium ions formed by the spontaneous β decay of [1,4‐3H2]benzene have been allowed to react with gaseous alcohols (ROH: R = Et, CF3CH2, Pr, or i‐Pr; partial pressure: 3–56 Torr) and alkyl chlorides (R′Cl: R′ = Pr, i‐Pr, or Bu; partial pressure: 20–450 Torr), in the presence of a thermal radical scavenger (O2: 4 Torr). Phenylium ion confirms its considerable site selectivity, demonstrated by the distinct preference toward the n‐centre of the substrate (46–100%), although significant insertion into the alkyl group of alcohols is observed as well. Phenylium ion displays significant positional selectivity even between different n‐type sites in a bidentate molecule such as CF3CH2OH. An affinity F < O < Cl trend is observed, which indicates a direct relationship between the polarizability of the n‐centre of the molecule and its orienting properties toward phenylium ion. The stability features of the ionic intermediates from addition of phenylium ion with ROH or R′Cl have been evaluated, as well as their fragmentation and isomerization mechanisms. The behaviour of phenylium ion toward the selected substrates in the gas phase is discussed and compared with previous mechanistic hypotheses from related nuclear‐decay studies.
Die Synthese und der thermische Zerfall des 1,2‐Diazabenzo[e]‐semibullvalens und dessen Beziehung zur Thermolyse des Benzobenzvalens
Authors: Burger Ulrich , Mentha Yves , Jean Thorel Pierre
Published: December 2004

The Synthesis and the Thermal Decay of 1,2‐Diazabenzo[e]semibullvalene and its Relation to the Thermolysis of Benzobenzvalene

The [4 + 2]‐photoadduct of naphthalene and 4‐phenyl‐4H‐1,2,4‐triazol‐3,5‐dione (PTAD) was subjected to a triplet‐sensitized di‐π‐methane rearrangement. Hydrolysis of the resulting urazol 15 gave a stable semicarbazide 16 which by nickel‐peroxide oxidation gave 1,2‐diazabenzo[e]semibullvalene (10). At 40 °C, the latter decays in CHCl3 solution to produce benzofulvene (2) as the principal product, accompanied by benzobenzvalene (1) and small amounts of naphthalene. This decay reaction is rationalized in terms of a 1,3‐dipolar cycloreversion which is followed by denitrogenation to give indenyl carbene (19). The thermolysis of 1 in solution is believed to proceed via the same carbene. At present, these findings provide only a partial answer to the benzobenzvalene enigma (i.e., in solution at 150°, 1 gives 2, but in the gas‐phase at 300°, 1 yields naphthalene). MeOH is shown to add readily to 10 in a homologous Michael addition.
Approaches to 1H‐Cyclopropa[l]phenanthrenes. Eliminations with 1a,9b‐Dihydro‐1H‐cyclopropa[l]phenanthrene Derivatives
Authors: Müller Paul , Thi Huong Can Nguyen , Pfyffer Jean
Published: December 2004

Base‐induced elimination of the sulfonium salt2iin the presence of furan affords the addition products7and8, derived from 1H‐cyclopropa[l]phenanthrene (1) and the isomeric cyclopropene5a(Scheme 3). Upon oxidation, the selenide2cyields phenanthrene‐9‐methanol (9), presumablyvia1. No evidence for the intermediate1is obtained from sulfoxide pyrolysis with2e, which leads to products formed by radical pathways(Scheme 5). Reductive elimination of the disulfone3bgives half‐reduction to monosulfone2gand complete reduction to cyclopropane2as well as 9‐methylphenanthrene (15), but no evidence for the intermediate1.
Intramolecular Oxygen Transfer on the Ozonolysis of a Diphenylcyclopentene Derivative
Authors: Jefford Charles W. , Boukouvalas John , Jaggi Danielle , Kohmoto Shigeo , Bernardinelli GéRald
Published: December 2004

The ozonolysis of cis‐3,4a,7,7a‐tetrahydro‐3,3‐dimethyl‐6,7a‐diphenylcyclopenta[1,2,4]trioxine (1) in CH2Cl2 at −78° gave the secondary endo ozonide 2 (43% yield) and an acetal 3 (27% yield) derived from O‐insertion at the ortho position of the C(7a) phenyl substituent. Both structures were elucidated by X‐ray. Repetition of the ozonolysis in MeOH/CH2Cl220:3 at −78° also gave the same two products in 12 and 15% yields, repectively, together with the hemiperacetal 4 (54% yield) formally derived from the secondary ozonide by addition of MeOH.
(+)‐(5R,6S)‐2‐(1′‐Aminoalkyl)‐6‐(hydroxyalkyl)penem‐3‐carboxylic Acids
Authors: Lang Marc , Hungerbühler Ernst , Schneider Peter , Scartazzini Riccardo , Tosch Werner , Konopka Edward A. , Zak Oto
Published: December 2004

In continuation of our work on penem antibiotics, novel chiral (5R,6S)‐2‐(1′‐aminoalkyl)‐6‐(hydroxyalkyl)‐derivatives1have been synthesized by two essentially different strategies. Whereas the starting materials for1a‐f, azetidinones2and5, were obtained from chiral building blocks (6‐aminopenicillanic acid and L‐threonine, resp.), the one for1g, azetidinone9, was derived from racemic 4‐acetoxyazetidinone and, as chiral auxiliary, (2R)‐2‐mercaptopropan‐1‐ol. The 2‐aminomethyl derivatives1a(CGP 30 779) and1f(CGP 31 608) proved the most potent compounds in the antibacterial testsin vitroand showed a well‐balanced spectrum of activity by comparison with that of established β‐lactams.
Membrane Structure of Substance P. I. Prediction of Preferred Conformation, Orientation, and Accumulation of Substance P on Lipid Membranes
Authors: Schwyzer Robert , Erne Daniel , Rolka Krzysztof
Published: December 2004

Preferred conformation, orientation, and accumulation of substance P on a neutral hydrophilic‐hydrophobic interface was estimated and extrapolated to interactions with neutral and anionic lipid bilayer membranes according to our general procedure. Nine residues at the C‐terminus were predicted to be transferred to the hydrophobic phase as an α‐helical domain, oriented quite perpendicularly on the membrane surface. The N‐terminal residues remained in the aqueous phase with their charges exposed to H2O. The molecular amphiphilic moment vector was strong (338 arbitrary units) and pointed its hydrophilic end towards the N‐terminus, only 15° away from the helix axis. The molecular electric dipole moment vector was also strong (124 debye) and pointed its positive end towards the N‐terminus, only 9° away from the helix axis. Thus, it reinforced the effect of the amphiphilic moment of a peptide intruding into the membrane dipole layer. The estimated dissociation constant for the equilibrium between membrane‐bound and free substance P was Kd ≈︁ 46 mM for neutral membranes, and Kd ≈︁0.43 mM for anionic membranes with a Gouy‐Chapman surface potential of −40 mV. Thus, substance P behaved similarly to dynorphin A and adrenocorticotropin peptides which insert their N‐terminal message segments as perpendicularly oriented helical domains into membranes, whereas their C‐terminal address segments remain in the aqueous phase as random coils. Substance P is the first instance of a neuropeptide which is expected to insert a C‐terminal message into lipid membranes.
Membrane Structure of Substance P. II. Secondary Structure of Substance P, [9‐Leucine]substance P, and Shorter Segments in 2,2,2‐Trifluoroethanol, Methanol, and on Liposomes Studied by Circular Dichroism
Authors: Rolka Krzysztof , Erne Daniel , Schwyzer Robert
Published: December 2004

Comparative CD studies with substance P (1), [Leu9]substance P ([Leu9]‐1), and their shorter peptide segments supported the membrane structures predicted for substance P and [Leu9]substance P. They indicated that the C‐terminal segments (from residue 3 or 4 onward) can adopt α‐helical conformations in hydrophobic environments and on lipid membranes. The N‐terminal segment, (residues 1–4) had a poly(proline)‐like conformation in aqueous and hydrophobic surroundings. Residues 3 and 4 (Lys‐Pro) appeared to belong to both domains and bring about the transition between the two. The estimated free energies of transfer for 1 and [Leu9]‐1 from their random conformations in H2O to their partially helical conformations on an aqueous‐hydrophobic interface are too small to allow detectable interaction with neutral lipid membranes at low concentrations. The two peptides should, however, interact detectably with anionic membranes because of favourable Boltzmann distribution factors. This prediction was shown to be correct for liposomes prepared from 1,2‐dioleoyl‐sn‐glycero‐3‐phosphocholine (neutral) and phosphatidylserine (anionic).
IR Laser Chemistry and CF Chromophore Absorption of 1,2‐Dichloro‐1,1,2‐trifluoroethane
Authors: Lupo Donald W. , Quack Martin , Vogelsanger Beat
Published: December 2004

The photochemical‐reaction yields after IR multiphoton excitation of CHFCl‐CF2Cl are reported and evaluated in terms of the steady‐state rate coefficient for reactant decay

The dominant primary reaction channels are α,β HCl and HF elimination, although minor pathways seem to include Cl2 elimination and other channels, which are discussed. The major uncertainty in the comparison with theoretical estimates resides in the fraction of CF chromophore band strength which contributes to excitation. The total band strength for the range from 940 cm−1 to 1310 cm−1 is reported to be G = ∫σ(ṽ) (dṽ/ṽ) = 8.2 pm2.
A Short Synthesis of (±)‐(cis‐6‐Methyltetrahydropyran‐2‐yl)Acetic Acid, a Constituent of Civet
Authors: Nussbaumer Cornelius , Fráter Georg
Published: December 2004

The title compound has been synthesized in four steps from (±)‐4‐penten‐2‐ol via a novel β‐alkenyloxyacrylate cyclization reaction 3→6 as the key step (overall yield 35%).
Steric Effects on Reaction Rates. Part IX. Force‐Field Parameters for Bridgehead and Rigid Tertiary Carbenium Ions
Authors: Müller Paul , Mareda Jiri
Published: December 2004

Molecular‐mechanics calculations for strain of carbenium ions are tested using Bentley's unified reactivity scale for bridgehead solvolysis as reference. Excellent correlations are obtained for solvolytic bridgehead reactivity with the calculated steric‐energy difference (ΔEst) between substrate (RH or ROH) and cation (R+). After adjustment of appropriate force‐field parameters, the approach is successfully extended to the rigid, but planar cations derived from structures 15–20; however, the general set of parameters cannot be applied to highly strained systems such as the cation formed from 17. With all of the 18 sets of parameters tested, the 2‐endo‐norbornyl derivative 16, is adequately correlated, while the exo isomer 15 exhibits enhanced reactivity by a factor of ca. 102 to 103.
Synthese makrocyclischer, α,β‐ungesättigter γ‐Oxolactone durch Ringerweiterungsreaktionen; ein neuer Weg zum makrocyclischen Lacton‐Antibiotikum A 26771 B
Authors: Bienz Stefan , Hesse Mauhad
Published: December 2004

Synthesis of Macrocyclic α,β‐Unsaturated γ‐Oxolactones by Ring‐Enlargement Reactions; a New Path to the Macrocyclic Lactone Antibiotic A 26771 B

A new synthetic route to the α,β‐unsaturated γ‐oxolactones 2a and 2b, involving two ring‐enlarement reactions, is described. Ring opening of bicyclic α‐nitroketones of the type 3 gave ring‐enlarged compounds of the type 4 which were converted to monoprotected diketones of the type 10 by using a variation of the Nef reaction as a key step. Macrocyclic lactones of the type 11 were obtained by Baeyer‐Villiger oxidation and converted into compounds of the type 2. The conversion of 2b to the macrocyclic lactone antibiotic A 26771 B (1) is already described in the literature.
Synthese Eines Optisch Aktiven Penem‐Zwischenprodukts Mittels Asymmetrischer Amidoalkylierung
Authors: Allmendinger Thomas , Rihs Grety , Wetter Hansjürg
Published: December 2004

Synthesis of an Optically Active Penem Intermediate by Asymmetric Amidoalkylation

The amidoalkylation of an optically active, cationic glycine derivative with methyl acetoacetate furnishes an intermediate 10a (Scheme 2) that is transformed in six steps to the optically active, silyl‐protected 4‐acetoxy‐3‐(1‐hydroxyenthyl)‐2‐azetidinon 18a, a well known intermediate in penem synthesis.
Dediazoniations of arenediazonium ions part 25 Influence of Substituents on the Exchange of the Diazonio Group for External Molecular Nitrogen and on the N(α), N(β)‐Rearrangement in the Diazonio Group
Authors: Ravenscroft Michael D. , Zollinger Heinrich
Published: December 2004

The N(α), N(β)‐rearrangement of the two N‐atoms which can be observed in solutions of [β‐15N]‐labelled p‐substituted benzenediazonium ions follows dual substituent parameter treatments. The reaction yields a negative field and a positive resonance reaction constant (pF =−3.35, pR = 2.47). The magnitude of these constants is, within experimental error, the same as the respective reaction constants for solvolytic dediazoniation. The exchange of the diazonio group of 15N‐labelled p‐substituted benzenediazonium ion yields, however, field and resonance reaction constants which are close to zero. This result is attributed to cancellation of the reaction constants for the forward and reverse steps in the complex mechanism of the exchange reaction.
Metal Complexes with Macrocyclic Ligands. Part XXVIII.. Structures and stabilities of the Cu2+ complexes with 1,4,7‐triazacyclononane‐1‐acetic acid
Authors: Studer Martin , Riesen Andreas , Kaden Thomas A.
Published: December 2004

The potentiometric study of the complexation of 1,4,7‐triazacyclononane‐l‐acetic acid (1) with Cu2+ (I = 0.5 (KNO3), T = 25°) indicates the presence of the species [Cu(1)], [Cu(1)OH], [Cu(1)2], and [(Cu(1))2OH], the stability constants of which are determined. The two complexes [Cu(1)]ClO4 and [(Cu(1)2)OH]ClO4 were also characterized by X‐ray structure analysis. In both cases, the Cu2+ ion is in a distorted square‐pyramidal arrangement, penta‐coordinated by the three N‐atoms of the macrocycle, an O‐atom of the carboxylate, and an additional O‐atom either from a second carboxylate or from an OH−, acting as a bridge between two metal centres.
Asymmetric Induction on Copper(I) Chloride catalyzed 1,4‐addition of alkylmagnesium chlorides to α, β‐disubstituted (E)‐enoylsultams and subsequent protonation
Authors: Oppolzer Wolfgang , Kingma Arend J.
Published: December 2004

Successive treatment of conjugated N‐enoylsultams 2 with alkyl Grignard reagents/CuCl and aq. NH4Cl solution generated selectively two stereogenic centers at C(α) and C(β) providing, after flash chromatography and crystallization, acylsultams 5 in high purity. Mild cleavage afforded the recovered sultam auxiliary 1 and enantiomerically pure carboxylic acids 7.
Synthesis of cycloproparenes via aromatization of 7‐Oxanorbornenes with Low‐Valent titanium
Authors: Müller Paul , Schaller Jean‐Pierre
Published: December 2004

1H‐Cyclopropa[b]naphthalene 3c and the 2,7‐diphenyl‐substituted derivative 3a have been synthesized via cycloaddition of the appropriate isobenzofurans 1a and 1b to 1‐bromo‐2‐chlorocyclopropene and aromatization of the adducts with low‐valent Ti. The same procedure afforded the 2,7‐dimethyl‐H‐cyelopropa[g]isoquinoline (15), but failed for the parent azacompound. Reaction of adducts of furans to 1‐bromo‐2‐chlorocyclopropenes with low‐valent Ti produced mixtures of cyclopropabenzenes 19 and 1,6‐dihalogeno‐1,3,5‐cycloheptatrienes 18. The latter could be converted to cyclopropabenzenes with BuLi.
Thermal Valence Rearrangements of Heterocycles. Part 2. A new synthetic approach towards the indole ring system
Authors: Bennett Grace A. , Mullen George B. , Georgiev Vassil St.
Published: December 2004

A new synthetic approach towards the indole ring system is described. When dimethyl 1‐methyl‐2‐oxa‐1‐aza‐spiro[4.5]dec‐3‐ene‐3,4‐dicarboxylate (6) was refluxed in toluene, the previously known dimethyl 4,5,6,7‐tetra‐hydro‐1‐methyl‐1H‐indole‐2,3‐dicarboxylate (7) was obtained in 71% yield, via a 2,3‐dihydroisoxazole‐pyrrole rearrangement. After treatment with DDQ, the tetrahydro analogue 7 was converted to the corresponding dimethyl 1‐methyl‐1H‐indole‐2,3‐dicarboxylate (8).
Technical Procedures for the Syntheses of Carotenoids and Related Compounds from 6‐Oxo‐isophorone: Syntheses of (3R,3′R)‐Zeaxanthin. Part I
Authors: Widmer Erich , Soukup Milan , Zell Reinhard , Broger Emil , Wagner Hans Peter , Imfeld Marquard
Published: December 2004

Starting from the readily available, optically active (4R)‐4‐hydroxy‐2,2,6‐trimethylcyclohexanone (1), a new technical synthesis of (3R,3′R)‐zeaxanthin is described. According to a 2(C9 + C6) + C10 = C40 construction scheme, the ketone 1 was first transformed with (E)‐3‐methylpent‐2‐en‐4‐yn‐1‐ol (5) into a C15‐intermediate which, by a three‐step sequence, could be converted into the known olefinic C15‐Wittig salt 4. Optimized conditions for the final Wittig reaction of 4 with the C10‐dialdehyde 3 are discussed. Based on 1, the overall yield of the entire technical process is ca. 40%.
Reduction of Indolin‐2‐ones and Desulfurization of Indoline‐2‐thiones to Indoline and Indole Derivatives
Authors: Nishio Takehiko , Okuda Norikazu , Kashima Choji
Published: December 2004

Reduction of indolin‐2‐ones with lithium aluminium hydride (LAH) or diisobutylaluminum hydride (DIBAL) and desulfurization of indoline‐2‐thiones with Raney‐Ni were investigated. Treatment of indoline‐2‐ones 1 with LAH or DIBAL yield indoles 4 and/or indolines 3 in moderate‐to high yield depending on the substituents at N and C(3) of 1. Indoline‐2‐thiones 2 were desulfurized with Raney‐Ni to give indoles 4 and/or indolines 3.
Relative Configuration and Conformation of 5‐(Dimethoxyphosphoryl)‐2‐methoxy‐1,2λ5‐oxaphospholan‐2‐ones by Multinuclear NMR Spectroscopy
Authors: Kalchhauser Hermann , Öhler Elisabeth
Published: December 2004

Information on the hitherto unknown relative configuration and on the conformation of the title compounds in solution can be derived from nuclearOverhausereffects and coupling constants. Whereas the bridged 5‐(dimethoxyphosphoryl)‐2‐methoxy‐1,2λ5‐oxaphospholan‐2‐ones6and7are sterically strained and, therefore, conformationally rigid, the C(3)‐unsubstituted compound1does not show a preferred solution conformation. Phenyl substituents at C(3) (compounds2–5) tend to adopt a pseudoequatorial position, this way leading to a definite conformation of the respective compounds. The influence of the conformation on the NMR spectra is discussed.31P‐NMR Spectroscopy is ideally suited for the characterization and quantification of the isomers2–5present in the reaction mixture.
Rogiolenyne D, the likely immediate precursor of rogiolenyne A and B, branched C15 acetogenins isolated from the red seaweed Laurencia microcladia of II Rogiolo. Conformation and absolute configuration in the whole series
Authors: Guella Graziano , Mancini Ines , Chiasera Giuseppe , Pietra Francesco
Published: December 2004

It is shown that in the red seaweed Jaurencia microcladia, collected in the Mediterranean off the torrent Il Rogiolo, the new branched C15 acetogenin rogiolenyne D ( = (+)‐(2S,3S,7R))‐3‐(bromomethyl)‐7‐[(Z)‐1‐chlorohexen‐3‐en‐5‐nyyl)]‐2‐ethyl‐2,3,6,7‐tetrahydrooxepin; (+)‐−3 co‐occurs with the already reported rogiolenyne A ((−)‐1) and B ((−)‐2a, suggesting the lineage (+)‐3→(−)‐1(−)‐2a,Which is realized here chemically. The relative configurations are established via NMR analysis and chemical transformations as regards the seven‐membered ring, while recourse is made to conformational analysis for the side chain. The absolute configuration is established via the Mosher's NMR method applied to the MPTA esters of (−)‐2a.
Glycosylidene Carbenes. Part 6. Synthesis of alkyl and fluoroalkyl glycosides
Authors: Briner Karin , Vasella Andrea
Published: December 2004

The syntheses of glycosides from the diazirine 1 and a range of alcohols under thermal and/or photolytic conditions are described. Yields and diastereoselectivities depend upon the pKHA values of the alcohols, the solvent, and the reaction temperature. The glycosidation of weakly acidic alcohols (MeOH, EtOH, i‐PrOH, and t‐BuOH, 1 equiv. each) in CH2Cl2 at room temperature leads to the glycosides 2–5 in yields between 60 and 34% (Scheme 1 and Table 1). At −70 to −60°, yields are markedly higher. In CH2Cl2, diastereoselectivities are very low. In THF, at −70 to −60°, however, glycosidation of i‐PrOH leads to α‐D‐/β‐D‐4 in a ratio of 8:92. More strongly acidic alcohols, such as CF3CH2OH, (CF3)2 CHOH, and (CF3)2C(Me)OH, and the highly fluorinated long‐chain alcohols CF3(CF2)5(CH2)2OH (11) and CHF2(CF2)9CH2OH (13) react (CH2Cl2, r.t.) in yields between 73 and 85% and lead mainly to the β‐D‐glucosides β‐D‐6 to β‐D‐8, β‐D‐12, and β‐D‐14 (d.e. 14–68%). Yields and diastereoselectivities are markedly improved, when toluene, dioxane, 1,2‐dimetoxyethane, or THF are used, as examined for the glycosidation of (CF3)2C(Me)OH, yielding (1,2‐dimethoxyethane, 25°) 80% of α‐D‐/ β‐D‐8 in a ratio of 2:98 (d.e. 96%; Table 4). In EtCN, (CF3)2C(Me)OH yields up to 55% of the imidate 10. Glycosidation of di‐O‐isopropylideneglucose 15 leads to 16 (CH2Cl2, r.t.; 65%, α‐D/ β‐D = 33:67). That glycosidation occurs by initial protonation of the intermediate glycosylidene carbene is evidenced, for strongly acidic alcohols, by the formation of 10, derived from the attack of (CF3)2MeCO− on an intermediate nitrilium ion (Scheme 4), and for weakly acidic alcohols, by the formation of α‐D‐9 and β‐D‐9, derived by attack of i‐PrO− on intermediate tetrahydrofuranylium ions. A working hypothesis is presented (Scheme 3). The diastereoselectivities are rationalized on the basis of a protonation in the σ plane of the intermediate carbene, the stabilization of the thereby generated ion pair by interaction with the BnOC(2) group, with the solvent, and/or with the alcohol, and the final nucleophilic attack by RO− in the π plane of the (solvated) oxonium ion.
An Alternative Access to (±)‐α‐Irones and (±)‐β‐Irone via Acid‐Mediated Cyclisation
Authors: Schulte‐Elte Karl H. , Pamingle Hervé , Uijttewaal Arnold P. , Snowden Roger L.
Published: December 2004

Acid‐mediated cyclisation of trienone 8, readily available from 2,3‐dimethylbutanal (1; five steps: 47% yield), using fluorosulfonic acid (6.8 mol‐equiv.) in 2‐nitropropane at −70°, afforded a 14:9:1 mixture (70% yield) of (±)‐cis‐α‐irone (9), (±)‐trans‐α‐irone (10), and (±)‐β‐irone (11). Other acidic conditions examined, using 95% aq. H2SO4 solution, 85% aq. H3PO4 solution, or SnCl4, gave inferior results.
Structural and Photophysical Properties of Lanthanide Nitrate 1:1 Complexes with planar tridentate nitrogen ligands analogous to 2,2′:6′,2′‐terpyridine
Authors: Piguet Claude , Williams Alan F. , Bernardinelli Gérald , Moret Emmanuel , Bünzli Jean‐Claude G.
Published: December 2004

The ligand 2,6‐bis(1‐methylbenzimidazol‐2‐yl)pyridine (mbzimpy, 1) reacts with EuIII to give [Eu(mbzimpy)(NO3)3(CH3OH)] [4] whose crystal structure (EuC22H21N8O10, a = 7.658(3) Å, b = 19.136(2) Å, c = 8.882 Å, β = 104.07(1)°, monoclinic, P21, Z = 2) shows a mononuclear structure where EuIII is ten‐coordinate by a meridional tridentate mbzimpy ligand, three bidentate nitrates, and one CH3OH molecule, leading to a low‐symmetry coordination sphere around the metalion. Essentially the same coordination is found in the crystal structure of [Eu(obzimpy)(NO3)3] (8) (EuC35H45N8O9, a = 9.095(2) Å, b = 16.624(2) Å, c = 26.198(6) Å, β = 95.85(1)°, monoclinic, P21/c, Z = 4) obtained by reaction of 2,6‐bis(1‐octylbenzimidazol‐2‐yl)pyridine (obzimpy, 2) with EuIII. Detailed photophysical studies of crystalline [Ln(mbzimpy)(NO3)3(CH3OH)] and [Ln(obzimpy)(NO3)3] complexes (Ln = Eu, Gd, Tb, Lu) show that 1 and 2 display 1ππ* and 3ππ* excited states very similar to those observed in 2,2′:6′,2″‐terpyridine, leading to efficient ligand to LnIII intramolecular energy transfer. Spectroscopic results show that an extremely efficient mbzimpy‐to‐EuIII transfer occurs in [Ln(mbzimpy)(NO3)3(CH3OH)] and in the case of TbIII, a TbIII‐to‐mbzimpy back transfer is also implied in the deactivation process. The origin of these peculiar effects and the influence of ligand design by going from mbzimpy to obzimpy are discussed. 1H‐NMR and luminescence data indicate that the structure found in the crystal is essentially maintained in solution.