bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Selectivities Disguised by Mass Diffusion. VII. A simple model of pH‐dependence of product distribution in mixing‐disguised azo coupling reactions. 8th Communication on the selectivity of chemical processes
Authors: Belevi Hasan , Bourne John R. , Rys Paul
Published: December 2004

In the present work a mixing‐reaction model is developed to describe the influence of the space‐ and time‐dependent concentration of the leaving group on the pre‐equilibria of the reactants and thus on the product distribution of mixing‐disguised reactions. The modelling is carried out using a typical example of such reactions, namely azo coupling, where the leaving group is a proton. For this reaction, the existence of characteristic sets of parameters is established, for which the product distribution does not depend on the initial pH‐value. These sets of parameters define the isoselectivity points.
Chemical Selectivities Disguised by Mass Diffusion. IX. A simple model of mixing‐disguised reactions in a continuous, stirred tank reactor. 10th Communication on the selectivity of chemical processes
Authors: Belevi Hasan , Bourne John R. , Rys Paul
Published: December 2004

A mixing‐reaction model ‘MIRE‐CSTR’ is developed to describe the selectivity behaviour mixing‐disguised reactions in continuous stirred tank reactors (CSTR). For competitive, consecutive reactions the general behaviour is demonstrated and a comparison with the behaviour in discontinuous operation is made. Furthermore, the start‐up process of the CSTR is discussed with the help of a model similar to the model ‘MIRE‐CSTR’.
Stereoselective Introduction of Steroid Side Chains at C (17) and C (20)
Authors: Batcho Andrew D. , Berger Donald E. , Davoust Stephen G. , Wovkulich Peter M. , Uskoković Milan R.
Published: December 2004

A simple and efficient new method for the highly stereoselective (at C (17) and C (20)) introduction of steroid side chains which are suitably functionalized for further elaboration is presented. The ene reaction of (17 Z)‐ethylidene steroids, which are readily obtained from 17‐keto steroids via a Wittig reaction, with various enophiles such as formaldehyde and acrylate esters leads to useful intermediates which contain the natural steroid configuration at C (20). Catalytic hydrogenation of the Δ16‐double bond occurs from the α‐face to stereospecifically generate the correct configuration at C (17). An additional chiral center at C (23) is also introduced stereoselectively by the use of methyl 2‐chloroacrylate as the enophile.
Photochemical free radical formation from aliphatic dicarboxylic acids in solution as studied by electron spin resonance spectroscopy
Authors: Wymann Lotty , Kaiser Tony , Paul Henning , Fischer Hanns
Published: December 2004

Various free radicals formed during UV.‐irradiation of aliphatic dicarboxylic acids in aqueous and methanolic solution are identified by ESR.‐spectroscopy. Their structures point to α‐cleavage and photoreduction as the dominant primary photochemical decay processes. The relative contributions of these reactions to the overall photodecomposition depend on solvent and degree of α‐alkylation of the acid. Emission ESR.‐spectra are found for radicals formed by C, CO‐bond cleavage of α‐dimethyl substituted acids. The polarization is referred to the triplet mechanism of CIDEP. and indicates this cleavage reaction occurs from a triplet molecular state.
Revidierte Struktur des Makrodiolids Colletodiol
Authors: Amstutz René , Hungerbühler Ernst , Seebach Dieter
Published: December 2004

Revised Structure of the Macrodiolide Colletodiol

An X‐ray analysis shows that the vicinal glycol unit of colletodiol has the threo‐rather than the previously assigned erythro‐configuration (see 1, Fig. 1 and Fig. 3). Together with the correlative assignments of (2R)‐ and (8R)‐absolute configurations by MacMillan & Simpson the centers of chirality of colletodiol 1 are now established to be (2R, 8R, 10R, 11R).
Ungewöhnliches Strukturmerkmal kristalliner Phthalsäure
Authors: Ermer Otto
Published: December 2004

Unusual Structural Feature of Crystalline Phthalic Acid

In crystalline phthalic acid the strain resulting from repulsion between the carboxylic groups is only partially relieved by rotating these groups out of the plane of the benzene ring around the (HOO)CC bonds. This is also achieved through a surprisingly large deviation of 20.3 (1)° from planarity of the (HOO)CCCC (OOH) torsion angle, as confirmed by an accurate redetermination of the crystal structure. This torsion angle may be smaller in the free molecule, i.e. packing forces appear at least partly responsible for its high value in the crystal.
Über Juliprosin, ein weiteres Alkaloid aus Prosopis julifloraA.DC. 180. Mitteilung über organische Naturstoffe
Authors: Dätwyler Peter , Ott‐Longoni Rita , Schöpp Emanuel , Hesse Manfred
Published: December 2004

Juliprosine, a Further Alkaloid Isolated from Prosopis juliflora A.DC.

By catalytic hydrogenation of the second base juliprosine (2) isolated from Prosopis juliflora (Leguminosae) the hexahydroderivative 5 was formed. The same product was obtained also by catalytic hydrogenation of juliprosopine (1) of known structure. The absolute configuration of 2 was deduced by comparison of [M]D values of Prosopis alkaloids of known absolute configuration.
Regioselective Alkylation of the Polyfunctional Nucleophile 1‐(Methylthio)‐3‐triethylsilyloxypentadienyllithium
Authors: Oppolzer Wolfgang , Snowden Roger L. , Briner Paul H.
Published: December 2004

γ‐Selective sulfenylation of the triethysilyloxypentadienyllithium 1 gave the versatile alkylthiodene 4 which on successive deprotonation and alkylation furnished with high regioselectivity the γ‐products 6. Fluoride‐promoted silylether cleavage 6 → 7 may be followed by intramolecular [4 + 2]‐addition 7c → 8 and sulfoxide elimination 8 → 9. The conversions 7b → 12 and 7a → 17 demonstrate the feasibility of 5 to serve as an equivalent of the hypothetical β‐deprotonated divinylketone 13 whose two enone units may be unmasked separately.
Effect of Self‐Assembly of Amphiphilic Redox‐Chromophores on Photoionization Processes
Authors: Humphry‐Baker Robin , Braun André M. , Grätzel Michael
Published: December 2004

A surfact derivative of phenothiazine was synthesized which is capable of micelle formation in aqueous solution. Concomitantly with micellization, strong changes in the photochemical behaviour occur. In particular, monophotonic photoionization is only observed above the critical micelle concentration (CMC.). Cooperative effects associated with self‐assembly of this amphiphilic redox chromophore leading to local electrostatic barriers are evoked to explain these effects.
Triplet Lifetime Determination of Molecules in the Gas Phase by T‐T Energy Transfer
Authors: Brühlmann Ueli , Huber J. Robert
Published: December 2004

It has been demonstrated that the triplet lifetime of nonemitting molecules in the dilute vapor phase ‐ even for complex triplet decays ‐ can be accurately determined by means of time‐resolved triplet‐triplet (T‐T) energy transfer to a strong emitter molecule. Besides the test molecules 1‐butyne‐3‐one and benzaldehyde the lifetime of the vibrationally relaxed nonemitting T1(nπ*) state of cycloheptanone, τ=63 ± 5 µs at ∼︁0.5 Torr, together with its energy transfer rate constant to biacetyl, kET=(1.80±0.08) x 106 s−1 Torr−1, have been measured.
Die Produkte der Thermolyse von N‐(1‐Pyridinio)‐2‐nitroaniliden sind keine Triaziridine, sondern 1, 2‐Bis[(2′‐nitrophenyl)‐azoxyl]‐benzole
Authors: Hilpert Hans , Hoesch Lienhard , Dreiding André S.
Published: December 2004

The products of the thermolysis of N‐(1‐pyridinio)‐2‐nitroanilides (1) had previously been interpreted as tris (2‐nitrophenyl)‐triaziridines (3). The present work shows them to be actually 1, 2‐bis[(Z)‐(2′‐nitrophenyl)‐ONN‐azoxy]benzenes (5). The revised structural assignment is based on the chemical and the spectroscopic (especially 1H‐NMR.) properties of 5 and on the results of a X‐ray structural analysis.
Carbon Participation in the Solvolysis of 6‐exo‐substituted 2‐exo‐ and 2‐endo‐Norbornyl p‐Toluenesulfonates. Norbornanes part 5
Authors: Fischer Walter , Grob Cyril A. , Hanreich Reinhard , von Sprecher Georg , Waldner Adrian
Published: December 2004

The solvolysis rates and products of the 6‐exo‐substituted 2‐exo‐ 1a‐1u, and 2‐endo‐norbornyl p‐toluenesulfonates 2a‐2u, have been determined. In general, the rate constants for 1 and 2 (log k) correlate well with the inductive constants σ of the substitutents at C(6); however, their sensitivity to σ is much larger in the 2‐exo‐series 1 than in the 2‐endo‐series 2. This differential transmission of polar effects is the cause of decreasing 2‐exo/2‐endo rate ratios from 2388 for R = t‐C4H9 to 0.37 for R = Br, i. e. with increasing electron attraction by the substituent. The high sensitivity of the rate constants for the 2‐exo‐p‐toluenesulfonates 1 to σ indicates an unusually strong inductive interaction between C(6) and the incipient cationic center at C(2). This interaction is ascribed to the participation of the pentacoordinate C(6)‐atom, i. e. to 1,3‐bridging, a consequence of steric hindrance of nucleophilic solvent participation in norbornanes. Donor substituents enhance 1,3‐bridging, lead to faster reactions and to the formation of 2‐exo substitution products. Conversely, acceptor substituents reduce 1,3‐bridging, decrease rates and facilitate the formation of 2‐endo substitution products. Graded 1,3‐bridging is discussed in the light of Winstein's nonclassical ion concept.
Synthetic Methods and Reactions. Part 106. Suppression of anchimerically assisted rearrangement products in the synthesis of α‐fluorocarboxylic acids from α‐amino acids with 48:52 (w/w) hydrogen fluoride/pyridine [1]
Authors: Olah George A. , Surya Prakash G. K. , Chao Yah Li
Published: December 2004

Anchimerically assisted rearrangement, observed in the fluorination of some α‐amino acids with 70 : 30 (w/w) hydrogen fluoride/pyridine (by weight) in the presence of NaNO2, is substantially or fully suppressed by using the less acidic reagent 48 : 52 (w/w) hydrogen fluoride/pyridine.
Crystal structure and electrical conductivity of nickel 6, 13‐di (p‐tolyl)‐5, 14‐dihydrodibenzo [b,i]‐1,4,8,11‐tetraaza [14]annulene Iodide (Ni (dtdbtaa)I2.58)
Authors: Hunziker Max , Loeliger Hans , Rihs Grety , Hilti Bruno
Published: December 2004

Single crystals of the title compound are monoclinic, space group P21/n with two formula units per cell of the following dimensions: a = 18.209, b = 19.076, c = 4.075 Å, β = 92.43°. The crystals show metallic conductivity along the needle axis from room temperature down to ca. 180 K, the maximum conductivity at room temperature being 455 (Ω cm)−1.

The unoxidized (iodine free) parent compound crystallizes n the monoclinic space group P21/c with 2 molecules per cell of dimensions: a = 4.988, b = 20.192, c = 11.871 Å, β = 94.41°.
Tetrameric Cubic Structures of Two Solvated Lithium Enolates
Authors: Amstutz René , Bernd Schweizer W. , Seebach Dieter , Dunitz Jack D.
Published: December 2004

The structures of the crystalline lithium enolates derived from 3, 3‐dimethyl‐2‐butanone and from cyclopentanone have been determined by X‐ray analysis. Both structures are tetrameric aggregates based on a Li4O4‐cube, each Li+‐ion being additionally bonded to the O‐atom of a tetrahydrofuran solvent molecule.
Mechanistic Implications of the Tetrameric Cubic Structure of Lithium Enolates
Authors: Seebach Dieter , Amstutz René , Dunitz Jack D.
Published: December 2004

The tetrameric cubic structure established for lithium enolates in the solid state is used as a model to discuss several facets of enolate chemistry: solubility, effects of cosolvents, addition to aldehyde and acid chloride, influence of mixed aggregates on diastereo‐ and enantioselectivities.
Contribution à la phytochimie du genre Gentiana. XXVI.. Identification d'une nouvelle di‐O‐glucosyl cinnamoyl‐C‐glucosylflavone extraite des feuilles de Gentiana X marcailhouana RY.
Authors: Luong Minh Duc , Saeby Jan , Fombasso Pierre , Jacot‐Guillarmod André
Published: December 2004

Phytochemistry of Genus Gentiana. XXVI. Identification of a New Di‐O‐glucosyl Cinnamoyl‐C‐glucosylflavone in the Leaves of Gentiana X marcailhouana RY.

A new di‐O‐glucosyl cinnamoyl‐C‐glucosylflavone has been identified as 4′‐O‐β‐D‐glucosyl‐2″‐O‐[2‐O‐β‐D‐glucosyl‐2,4,5‐trihydroxy‐(E)‐cinnamoyl]isoorientin (1).
Specificities of the α‐Alkynone‐Cyclization
Authors: Karpf Martin , Huguet Joan , Dreiding André S.
Published: December 2004

Spezifitäten der α‐Alkinon Cyclisierung

Die Regio‐ und Stereo spezifitäten der α‐Alkinon‐Cyclisierung, einer thermischen Umwandlung von Alkinyl‐alkyl‐ketonen, welche in β′‐Stellung mindestens ein H‐Atom tragen, zu 2‐Cyclopentenonen wurden untersucht. Cyclisierung zum höher substituierten C(β′)‐Atom ist dabei bevorzugt, vorausgesetzt, dass die zur Insertion zur Verfügung stehende C(β′), H‐Bindung zur Propioloylseitenkette eine möglichst synplanare Anordnung einnehmen kann. In Cyclisierungen zu β′‐Methylen‐C‐Atomen, welche diastereotope H‐Atome tragen, wird daher eines der möglichen epimeren Produkte bevorzugt oder ausschließlich gebildet. Die mechanistischen Konsequenzen der gefundenen Spezifitäten werden diskutiert.
Direct Observation of 103Rh‐Chemical Shifts in Mono‐ and Dinuclear Olefin Complexes
Authors: Maurer Ellen , Rieker Susanne , Schollbach Michael , Schwenk Andreas , Egolf Thomas , von Philipsborn Wolfgang
Published: December 2004

The 103Rh‐resonance has been investigated at 2.8 MHz in mono‐ and dinuclear olefin complexes by steady‐state NMR.‐pulse techniques. For dirhodium complexes with scalar Rh, Rh‐coupling, a selective rf‐irradiation was applied to improve sensitivity. Within the same measuring time the signal/noise ratio is improved by the factor (T2/T)1/2 by this steady‐state method in comparison with the usual free‐induction technique. (T1/T2)‐ratios, as obtained from the dependence of signal in tensity on the pulse‐flip angle are discussed in terms of relaxation mechanisms and chemical exchange phenomena. From (T1/T2)‐ and (T1 + T2)‐experiments, individual T1 and T2 values have been determined for C5H5RhC8H12 and Rh(acac)3.

The 103Rh‐chemical shifts of 39 olefin complexes are reported. Shielding depends upon the (formal) oxidation state of Rh whereby resonances of pure olefin complexes appear at the low‐frequency end of the δ‐scale, which extends over 10000 ppm. For cyclic 1,3‐diene ligands Rh‐shielding increases with decreasing ring size and decreases with further conjugation of the diene systems.

In the dirhodium complexes, Rh, Rh spin‐coupling constants are < 10 Hz. Rh, C‐coupling constants in (diene)RhCp‐complexes increase, for the terminal diene C‐at om, with increasing ring size of the 1,3‐diene, 1J(Rh, C) = 11.7 to 17.4 Hz.
A PCILO Study of Conformation and Internal Rotation in Mono‐substituted Benzenes
Authors: Gerhards Jürgen , Ha Tae‐Kyu , Perlia Xavier
Published: December 2004

The effect of Kékulé representation and hybrid function of O‐atoms in the PCILO‐CNDO framework of conformation and internal rotation in mono‐sub stituted benzenes Ph‐X (XNH2, OH, OCH3, CH3, CHO, NO2) is studied. Three variational criteria for the choice of the appropriate third‐order energy, proposed to symmetrize the PCILO results, are critically examined in relation with the height of rotational barrier in these molecules. The study shows that, in all cases, the most stable conformation is qualitatively correct predicted by the PCILO method. Since the barrier to internal rotation in the studied aromatic systems arises predominantly from delocalization effect, it is proposed to employ the arithmetic mean of the third‐order energy of the two Kékulé structures. In molecules, in which the third‐order energy between the two Kékulé structures is larger than 2 kcal/mol, however, the lower third‐order energy representation alone seems to be appropriate. In phenol and anisole the spa‐hybridization type of the O‐atoms offers better values of rotational barrier, whereas in the sp3‐type the delocalization is overestimated in the planar conformation.
Structure, Synthesis, and Properties of Some Persubstituted 1,2‐Dintroethanes. In Quest of Nitrocyclopropyl‐Anion Derivatives
Authors: Kai Yasushi , Knochel Paul , Kwiatkowski Stefan , Dunitz Jack D. , Oth Jean F. M. , Seebach Dieter , Kalinowski Hans‐Otto
Published: December 2004

Attempts to deprotonate nitrocyclopropane led to solutions which showed strong ESR. signals (Fig. 1)and from which 1‐nitro‐ l′‐nitroso‐bicyclopropyl (3) and 1,1′‐dinitro‐bicyclopropyl (2) were isolated. The activation energy for rotation about the central C, C‐bond of 2 is estimated to be about 12 kcal/mol (1 H‐NMR. spectra in Fig. 2). In contrast, the oven‐chain analogue 2,3‐dimethyl‐2,3‐dinitrobutane (1) shows a methyl singlet down to −70° C. Low‐temperature X‐ray analyses of 1, 2, 3, and also of 1,1′‐dinitro‐bicyclobutyl (4) show that all four molecules have gauche‐conformations but reveal striking structural differences between the openchain and the cyclic derivatives (Fig. 4–6): the central C, C‐bond is long in 1 (1.575 Å), short in 2 (1.479 Å); the C, N‐bonds are long in 1 (1.549 Å), short in 2 (1.488 Å); the orientation of the nitro groups is bisected in 2 and perpendicular in 1. The crystal structure of the nitro‐nitroso compound 3 is isomorphous with that of the dinitro compound 2 and thus disordered (Fig. 15–16). The effect of the nitro group as π‐electron acceptor on the molecular conformations and bond lengths is discussed. From analysis of the anisotropic vibrational parameters of 2 the root‐mean‐square librational amplitude of the nitro groups about their C, N‐bonds is estimated to be about 5.8° at 95 K, corresponding to a rotational barrier of about 9 kcal/mol, i. e. the same order of magnitude as the NMR. estimate of about 12 kcal/mol for C, C‐rotation.
On the Activity of Water and the Concept of the Interfacial Free Energy in W/O‐Microemulsions
Authors: Kubik Rudolf , Eicke Hans‐Friedrich , Jönsson Bengt
Published: December 2004

The water activity and its temperature dependence as a function of the amount of water in the L2‐phase of the (water/Aerosol OT/isooctane)‐system (s. Exper. Part) was determined with the help of a differential pressure gauge and a precision cathetometer. A theoretical approach based essentially upon a solution of the Poisson‐Boltzmann equation with appropriate boundary conditions led to a description of the activity plot in excellent agreement with experimental results.
Face Selectivity of the Diels‐Alder Additions of 2‐Substituted 5,6‐bis((E)‐chloromethylidene)bicyclo[2.2.2]octanes
Authors: Avenati Marco , Vogel Pierre
Published: December 2004

The preparation of 5,6‐bis((E)‐chlorommethylidene)bicyclo[2.2.2]oct‐2‐ene (13), 2,3‐bis((E)‐chloromethyl idene)‐5exo,6exo‐ and ‐5endo,6endo‐epoxybicyclo[2.2.2] octane (14 and 15), 5,6‐bis((E)‐chloromethylidene)‐2exo‐ and ‐2endo‐bicyclo[2.2.2] octanol (16 and 17) and 5,6‐bis((E)‐chloromethylidene)‐2‐bicyclo[2.2.2]octanone (18) are described. The face selectivity (endo‐face vs. exo‐face attack onto the exo‐cyclic diene) of their cycloadditions to tetracyanoethylene has been determined in benzene at 20°. It is 78/22, 80/20, 60/40, 68/32, 3/97 and 30/70 for 13, 14, 15, 16, 17 and 18, respectively.
Panicutin, ein neues Alkaloid aus Aconitum paniculatum LAM. 4. Mitteilung über Aconitum
Authors: Katz Alfred , Staehelin Esther
Published: December 2004

Panicutin, a New Alkaloid from Aconitum paniculatum LAM.

A new diterpene alkaloid, which we named panicutine (2), was isolated from the paniculatine‐containing chemovariety of Aconitum paniculatum LAM. Investigation by spectral methods showed that 2 has the formula C23H29N44 and belongs to the hetidine (1)‐type alkaloids. It has one acetoxy group at C(2) and one carbonyl group each at C (6) and C (11).
C45‐ and C50‐Carotinoide. 1. Mitteilung. Synthese von (R)‐ and (S)‐Lavandulol
Authors: Kramer Andreas , Pfander Hanspeter
Published: December 2004

C45‐ and C50‐Carotenoids, 1st Communication. Synthesis of (R)‐ and (S)‐Lavandulol

Starting with methyl (3 R)‐3‐hydroxybutanoate ((R)‐7) and ethyl (3 S)‐3‐ hydroxybutanoate ((S)‐11), respectively, (R)‐ and (S)‐lavandulol ((R)‐1 and (S)‐1) were synthesized with high optical purity. The synthesized key intermediates (R)‐6 and (S)‐6 are suitable compounds for the synthesis of optically active acyclic C45‐ and C50‐carotenoids.
Determination of the Relative Configurations in the Side Chains of the Antibiotics Hedamycin and Pluramycin A; Synthesis and NMR. Data of Suitable Model Compounds
Authors: Ceroni Mario , Séquin Urs
Published: December 2004

Several diepoxyhexanoates and epoxyhexenoates were prepared by epoxidation of methyl 2‐methyl‐2,4‐hexadienoate or by Darzens condensation. Their 1 H‐ and 13C‐NMR. spectra were measured and assigned. Comparison of these data with the spectra of the antibiotics hedamycin (1) and pluramycin A (2) allowed the determi‐nation of the relative configurations in the side chains of these antibiotics. They were found to be (14R*,16S*,17R*,18S*) for hedamycin (1) and (14R*,16S*,17Z) for pluramycin A (2).
On the Construction of the C/D‐Ring Systems of Aphidicolin and Stemodin: a Regio‐ and Stereospecific Synthesis of 17‐Noraphidicolaii‐16 one and 17‐Norstemodan‐16‐one Preliminary Communication
Authors: Bravetti Doriano , Bettolot Rinaldo Marini , Lupi Alessandro
Published: December 2004

A very simple regio‐ and stereospecific synthesis of 17‐noraphidicolan‐16‐one and 17‐norstemodan‐16‐one by solvolytic rearrangement of suitable bicyclo[2.2.2]‐‐octenyl methanesulfonate is described.
Eine einfache Synthese für 2‐Aminomethyl‐indene. 11. Mitteilung über metallorganische Reaktionen and Folgeprodukte
Authors: Marxer Adrian
Published: December 2004

To obtain the title compounds 1‐aminomethyl‐substituted α‐vinyl‐benzyl alcohols of type 13 are treated with concentrated sulfuric acid in acetic or propionic acid containing small amounts of their anhydrides to give aminomethyl ‐ indenes in excellent yield. Depending on the benzyl alcohols used, the new indenes are substituted at C(2) by an aminomethyl group, and at C(3) by various substituents, examples of which are given in Table 3, according to R in the benzyl alcohols of Table 1. To obtain a ring closure, the benzyl alcohol 13 must at least contain one free ortho position.

The starting benzyl alcohols are easily obtainable by Grignard reaction, e.g. from 2‐bromo‐3‐(dimethylamino)‐l‐propen, originally detected by Normant et al. [7], and various ketones.

If a tricyclic ketone is used, benzyl alcohols of types 19, 20 and 21 (Table 2) are obtained in excellent yields. From these, ring closures lead to tetracyclic compounds of types 22, 23 and 24 (Table 4) but in lower yields (13‐42%).
Identification and Synthesis of New γ‐Lactones from Tuberose Absolute (Polianthes tuberosa)
Authors: Maurer Bruno , Hauser Arnold
Published: December 2004

Six unsaturated γ‐lactones, (Z)‐5‐octen‐4‐olide (1), (Z)‐5‐decen‐4‐olide (2).(Z)‐6‐nonen‐4‐olide (3), (Z)‐6‐dodecen‐4‐olide (4), (Z, Z)‐6,9‐dodecadien‐4‐olide (5), and tuberolide (6) have been identified for the first time in tuberose absolute (from Polianthes tuberosa L.). All structures were corroborated by synthesis and all, except 3 and 4, are new.

The name ‘tuberolactone’ has been suggested for (Z, Z)‐2,7‐decadien‐5‐olide [1]. We propose the name ‘tuberolide’ for the bicyclic lactone 6. (IUPAC name (1R*,5S*,Z)‐6‐(2′‐pentenyl)‐2‐oxabicyclo[3.3.0]octan‐3‐one).

An improved method for the stereoselective synthesis of (±)‐cis‐bicyclo [4.3.0]‐non‐3‐en‐7‐one (23) by an AlCl3‐catalyzed Diels‐Alder reaction is reported.
Structures cristallines et moléculaires des muscs macrocycliques. I. La cis‐civettone et les variétés polymorphes α et β de sa 2,4‐dinitrophénylhydrazone
Authors: Bernardinelli Gérald , Gerdil Raymond
Published: December 2004

Crystal and Molecular Structure of Macrocyclic Musks. I. cis‐Civetone and polymorphous α‐ and β‐forms of his 2,4‐dinitrophenylhydrazone

cis‐Civetone (C17H30O) forms tetragonal plastic crystals, space groupe 141; a = 9.95(4), c = 32.79(1) Å; Z = 8. The plastic phase exists in a wide temperature range and 731 reflexions could be collected at 153 K. The highly disordered structure model was obtained by the use of direct methods. The molecules appear as ring‐shaped diffuse electron‐density distributions located in special position.

Two polymorphous crystalline forms were isolated for the 2,4‐dinitrophenyl‐hydrazone of cis‐civetone (DNPHCC). Both forms are triclinic, space group P1. Z = 2 (α‐Form: a = 6.279(5), b = 12.605(8), c = 15.253(10) Å, α = 105.49(7). β = 100.31 (6), γ = 91.23(7)°; β‐Form: a = 7.950(2). b = 8.405 (2). c = 18.233(4) Å, α = 100.28(2), β = 92.29(3), γ = 94.18(2)°). The structures were solved by direct methods and refined to R = 0.11. Each polymorph is associated with a different quinquangular conformation of the macrocycle. In the crystals the intermolecular interactions between macrocycles and aromatic substituents are minimized, the DNPH group being oriented in a face‐to‐face arrangement across a centre of symmetry.

Empirical force field calculations show that the overall intluence of the DNPH moiety on the attached cycle does not significantly modify its conformation with regard to that of the ketone itself.
Synthesis and Photo‐oxygenation of Some Substituted 1‐Benzyl‐3,4‐dihydroisoquinolines. Mechanism of Enamine Photo‐oxygenation
Authors: Martin Ned H. , Jefford Charles W.
Published: December 2004

The synthesis of a series of substituted 1‐benzyl‐3,4‐dihydroisoquinolines by Bischler‐Napieralski cyclization is described. Competitive methylene blue sensitized photo‐oxygenation experiments allowed the determination of relative rates of photo‐oxygenation of 1‐benzyl‐3,4‐dihydroisoquinolines, Substituents were shown to affect both the equilibrium concentration of the tautomeric enamine and the overall photo‐oxygenation rate. After correcting for differences in enamine concentration, the relative rate data provided a diagnostic probe of the reaction mechanism, which involves transfer of charge in the rate‐limiting step.
Technische Verfahren zur Synthese von Carotinoiden und verwandten Verbindungen aus 6‐Oxo‐isophoron. VI. Synthese Von Rhodoxanthin und (3‐RS, 3′RS)‐Zeaxanthin; Zugänge zur C15‐Ringkomponente über 3‐Oxo‐jonon‐Derivate
Authors: Widmer Erich , Soukup Milan , Zell Reinhard , Broger Emil , Lohri Bruno , Marbet Roman , Lukáč Teodor
Published: December 2004

Technical Procedures for the Synthesis of Carotenoids and Related Compounds from 6‐Oxo‐isophorone, VI. Synthesis of Rhodoxanthin and (3RS, 3′RS)‐Zeaxanthin; Routes to the C15‐Ring Component via 3‐Oxo‐ionone Derivatives

The C15‐ring component 4, key intermediate of a new scheme for the synthesis of rhodoxanthin (1) and (3RS, 3RS)‐zeaxanthin (3), has been synthesized starting from 6‐oxo‐isophorone (7) via 3‐oxo‐cyclocitral and 3‐oxo‐ionone derivatives.
High‐pressure [2 + 4]‐cycloaddition of dimethylmaleic anhydride to 3,4‐dimethoxyfuran; synthesis of dimethoxycantharidin preliminary communication
Authors: Jurczak Jamisz , Koz̀luk Tomasz , Filipek Stanislaw , Eugster Conrad Hans
Published: December 2004

As an active diene (more active than furan itself), 3,4‐dimethoxyfuran (1) affords with many dienophiles the respective cycloadducts in a high yield [2]. It has recently been found that under thermal conditions 1 easily reacts with maleic anhydride and its monomethyl derivative, but not with dimethylmaleic anhydride (2) [3]. This is probably due to steric hindrance resulting from the location of two methyl groups on the double bond of the dienophile. Since all Diels‐Alder reactions in particular those with steric hindrance are pressure‐sensitive [4]. we resolved to perform the title reaction under conditions of static high pressure.
Spectrophotometric and Nuclear Magnetic Resonance Study of Temperature‐ and Pressure‐induced Changes in the Intimate Solvation of Neodymium (III) in N, N‐Dimethylformamide and Trimethylphosphate
Authors: Pisaniello Dino L. , Nichols Peter J. , Ducommun Yves , Merhach André E.
Published: December 2004

The temperature‐ and pressure‐dependent equilibria for the addition of an extra N, N‐dimethylforrnamide (DMF) or trimethylphosphate (TMP) ligand onto [Nd (DMF)8]3+‐ and [Nd(TMP)6]3+‐species respectively have been measured by visible spectrophotometry. Complementary NMR. studies on other lanthanide ions show a gradual shift in preference for the lower coordination number across the lanthanide series.
Photochemical Synthesis of 2‐Alkylidene‐4‐pyrrolin‐3‐ones
Authors: Ghaffari‐Tabrizi Ramin , Margaretha Paul
Published: December 2004

Irradiation (λ =313 nm) of the 4‐pyrrolin‐3‐ones 1a–1c in acetone‐, 3‐pentanone‐and cyclopentanone solution affords the title compounds 2, formally via H‐abstrac‐tion by the excited ketone and recombination of the radical pair formed.
Diastereoselective Synthesis of Nitroaldol Derivatives
Authors: Seebach Dieter , Beck Albert K. , Mukhopadhyay Triptikumar , Thomas Elizabeth
Published: December 2004

Three methods are described by which diastereomerically enriched nitroaldols and their O‐silylated derivatives can be prepared. threo‐Nitroaldols prevail up to 10:1 over the erythro‐isomers if doubly deprotonated nitroaldols 28 are quenched with acetic acid (THF/HMPT or DMPU, − 100°) (see Scheme 5 and Table 2). O‐Trimethyl‐ or O‐(t‐butyl)dimethylsilylated (TBDMSi) erythro‐nitroaldols can be obtained by protonation of the corresponding lithium nitronates (35, 39) in THF at low temperature (see Schemes 6 and 7). The erythro‐O‐TBDMSi‐nitroaldol derivatives are also formed in the fluoride catalyzed addition of TBDMSi‐nitronates (40–45) to aldehydes (see Schemes 8 and 9), In the latter reaction no 1,2‐asymmetric induction is observed if a‐branched silylnitronates or aldehydes are employed (see 48/49 and 50/51) – The stereochemical course of the reactions leading to erythro‐O‐TBDMSi‐nitroaldols follows topological rules of broad applicability (see Scheme 10); possible mechnisms are discussed. ‐ The configuration of diasteromerically 13C‐NMR. Spectroscopy. – Some examples of the preparation of diastereimerically enriched 1,2‐aminolcohols by reduction of the correspondence nitro compounds without loss of configurational purity are described (see Schemes 11 and 12).
The Synthesis of 4,11,18,25‐Tetrachloro [14]metacyclophane‐7,14,21,28‐tetroi, Structural Analogues of Phloroglucides
Authors: Moshfegh Ali A. , Badri Rashid , Hojjatie Massoud , Kaviani Mehrangiz , Naderi Basirat , Nazmi Aboul H. , Ramezanian Merrikh , Roozpeikar Bizhan , Haakimelahi Gholam H.
Published: December 2004

The synthesis of the title compounds is described. Some of the compounds prepared exhibited antimicrobial activity in vitro. Structure‐activity relationship is briefly discussed.
Synthesen von tetrathiafulvalen‐homologen Molekülsystemen mit zentraler Bicyclo [4.4.1]undeca‐1(10),3,5,8‐tetraen‐2,7‐diyliden‐ und Bicyclo [4.4.1]undeca‐1(10), 3,6,8‐tetraen‐2,5‐diyliden‐Gruppe
Authors: Neidlein Richard , Zeiner Hartmut
Published: December 2004

Synthesen of Tetrathiafulvalene‐homologous Systems with Central Bucyclo[4.4.1]undeca‐1 (10), 3,5,8‐tetraen‐2, 7‐diyliden‐ und Bicyclo[4.4.1]undeca‐1 (10), 3,6,8‐tetraen‐2,5‐diyliden‐Gruppe

The syntheses, the spectroscopic and electrochemical properties of the heterocyclic‐substituted l,6‐Methano[10]annulene (= 1,6‐methanobicydo[4.4.1]deca‐1,3,5,7,9‐pentaene)‐derivatives 2 and 7 (derivatives of tetrathiafulvalene‐homologous systems) are described.
Polarographic Properties and Electrochemical Reduction of 1,2‐Dimethyl‐3‐indolyl Heteroaryl Ketones
Authors: Naef Rudolf
Published: December 2004

The reduction of a series of 1,2‐dimethyl‐3‐indolyl heteroaryl ketones, where the heteroaryl components are 2‐benzoxazolyl, 2‐behzpthiuzolyl. 1‐methyl‐2‐benz‐imidazolyl, 4‐ and 2‐pyridyl, in aprotic and prone solution are described by means of DC. and AC. polarography, cyclic voltammetry and coulometry.

In acetonitrile a two‐step reduction mechanism with a reversible first and an irreversible second one‐electron transfer has been observed, confirmed by AC.‐polarographic and cyclovoltammetric measurements. The reduction potentials, between −1.377 and −1.787 V for the first step, and between −1.937 and −2.250 V (vs. Ag/AgCl) for the second, could not be correlated with the LUMO energies from HMO calculations which was explained as being due to a distorted configuration of the π systems.

In protic media (ethanol/water) reduction occurs in an irreversible one‐step mechanism. Measurements of the pH dependence of the half‐wave potential in the pH* range 0–12 and the evaluated transfer coefficients show that the reduction step represents the transfer of two electrons and two protons yielding secondary alcohols and no dimerization products under any condition. These findings are supported by coulometric and macroscale electrolysis of the ketones; the products isolated were characterized by IR. and 1H‐NMR. data.
π‐Orbital Interactions in Möbius‐Type Molecules as Studied by Photoelectron Spectroscopy
Authors: Haselbach Edwin , Neuhaus Louis , Johnson Richard P. , Houk Kendall N. , Paddon‐Row Michael N.
Published: December 2004

Some benzobarrelenes were studied by photoelectron (PE.) spectroscopy. The results can be interpreted by considering dominant through‐space interaction of the π‐molecular fragments in a Möbius‐fashion, Some chemical features of the substrates are rationalized on the basis of these findings.
1,3‐Dipolare Cycloadditionen von 2‐(Benzonitrilio)‐2‐propanid mit 4,4‐Dimethyl‐2‐phenyl‐2‐thiazolin‐5‐thion und Schwefelkohlenstoff
Authors: Obrecht Daniel , Prewo Roland , Bieri Jost H. , Heimgartner Heinz
Published: December 2004

1,3‐Dipolar Cycloadditions of 2‐(Benzonitrilio)‐2‐propanide with 4,4‐Dimethyl‐2‐phenyl‐2‐thiazolin‐5‐thione and Carbon Disulfide

Irradiation of 2,2‐dimethyl‐3‐phenyl‐2H‐azirine (11) in the presence of 4,4‐dimethyl‐2‐phenyl‐2‐thiazolin‐5‐thione (7) yields a mixture of the three (1:1)‐ad‐ducts 8, 12 and 13 (Schemes 3 and 6). The formation of 8 and 12 can be explained by 1,3‐dipolar cycloaddition of 2‐(benzonitrilio)‐2‐propanide (1b) to the C, S‐double bond of 7. Photochemical isomerization of 12 leads to the third isomer 13 (Schemes 3 and 7). Photolysis of the azirine 11 in the presence of carbon disulfide gives a mixture of two (2:l)‐adducts, namely 12 and 13(Scheme 4). A reaction mechanism via the intermediate formation of the 3‐thiazolin‐5‐thione b is postulated. The structure of the heterocyclic spiro compound 13 has been established by single‐crystal X‐ray structure determination (cf. Fig. 1 and 2).
Speleands. Macropolycyclic receptor cages based on binding and shaping sub‐units. Synthesis and properties of macrocycle cyclotriveratrylene combinations. Preliminary communication
Authors: Canceill Josette , Collet André , Gabard Jacqueline , Kotzyba‐Hibert Florence , Lehn Jean‐Marie
Published: December 2004

Combination of a receptor unit with a rigid shaping unit produces a new type of receptor molecules of the cryptand class, hollow macropolycyclic molecules termed speleands, capable of substrate inclusion. Two members of this category of compounds 1 and 2, have been synthesized by connecting in a single step, a macro‐cyclic [18]‐N3O3 binding unit with a rigid cyclotriveratrylene unit via three bridges. Compound 1 binds the rnethylammonium cation forming both external and internal complexes; for the latter a ‘speleme’ structure, schematically represented by 15, may be proposed.
Synthesis of a Tetracyclo [4.4.0.02,4.03,8]decanone via Intramolecular Reductive Coupling
Authors: Margaretha Paul , Tissot Paul
Published: December 2004

The reduction of cis‐4 a‐methyl‐1,2,4a,7,8,8 a‐hexahydronaphthalene‐2,7‐dione (1) was studied by cyclic voltammetry and product analysis. On a preparative scale, 6‐hydroxy‐3‐methyltetracyclo[4.4.0.02,4.03,8]decan‐10‐one (2) was obtained in 22% yield via an intramolecular hydrodimerization/aldol reaction sequence. The CV. results (Hg, DMF) suggest that the cyclopropane ring is formed after the first electron transfer by coupling of the anion radical with the second C. C‐double bond.
Asymmetric Synthesis of α‐Aminophosphonic Acids by Cycloaddition of N‐Glycosyl‐C‐dialkoxyphosphonoylnitrones
Authors: Vaseila Andrea , Voeffray Robert
Published: December 2004

Addition of dialkyl phosphites to the nitrone 6, formed in situ from the oxime 5 and formaldehyde gave the hydroxylamines 7 (86%) and 8 (88%), which reacted with p‐benzoquinone in the presence of ethylene via the C‐dialkoxyphosphonoylnitrones 9 and 10 to yield the cycloaddition products 11–14 (80–85%) with a diastereoselectivity of about 50%. The cycloaddition products were transformed into the monoisopropylidene derivatives 15–18 and the diacetates 19–22. Comparison of the NMR spectra and the specific rotations of the compounds 19–22 with those of the corresponding α‐ammo‐acid derivatives 23–26 of known configuration indicated preferential formation of the L‐isomers. The cycloaddition products were transformed in good yield into the L‐α‐aminophosphonic acids 29, 30, 36, and 39.
The Electronic Structure of Pentaprismane (C10H10), as Revealed by its Photoelectron Spectrum
Authors: Honegger Evi , Eaton Philip E. , Shankar B. K. Ravi , Heilbronner Edgar
Published: December 2004

The photoelectron (PE.) spectrum of the title compound has been assigned by comparison with the PE. spectrum of cubane (2), aided by ab initio STO‐3G calculations using localized molecular orbitals. On the basis of the information available to date, the most satisfactory orbital sequence, Koopmans theorem implied, is, in descending order of energy: band system : (2e″2, 3e′2 2e″1, 3e′1); band system : 3a′1 (2e′2, 2a″2); band : 2e′1.(Sequence of orbitals in parenthesis uncertain).
Circular Dichroism of Some Isomeric Alkyl Pyridines
Authors: Pino Piero , Piccolo Oreste , Straub Barbara , Consiglio Giambattista , Tran Dich Cong
Published: December 2004

The UV. and CD. spectra of the optically active 2‐, 3‐ and 4‐(l‐methylpropyl)‐pyridines (1a, b, c) and of the corresponding (2‐methylbutyl)pyridines (2a, b, c) have been investigated in hexane at RT. and at −85°, in hexane/TFA and in aqueous HCl‐solution. In 1c and 2c both the n → π* and the π → π* transitions are optically active, an n → π* transition being located above 265 nm. The position and the sign of the CD. bands are greatly influenced by the position and the nature of the alkyl substituent.
The electron affinities of (E)‐ and (Z)‐cyclooctene. Preliminary communication
Authors: Allan Michael , Haselbach Edwin , von Büren Martin , Hansen Hans‐Jürgen
Published: December 2004

Electron transmission measurements yield vertical electron affinities of −1.93 eV for (Z)‐ and of −1.79 eV for (E)‐cyclooctene (Z and E, respectively). It is concluded that the ‘out of plane’ bending effect in torsioned E does not influence its LUMO‐energy to a larger degree than its HOMO‐energy (as determined by photoelectron (PE.) spectroscopy) with respect to non‐torsioned Z.
Diterpenoide Chinomethane, vinyloge Chinone und ein Phyllocladan‐Derivat aus Plectranthus purpuratus HARV. (Labiatae)
Authors: Katti Seturam Bandacharaya , Rüedi Peter , Eugster Conrad Hans
Published: December 2004

Diterpenoids from Leaf Glands of Plectranthus purpuratus: p‐Quinomethanes, Extended Quinones, p‐Acylcatechols and a Novel Phyllocladanon Derivative

From the complex mixture of terpenoids from the title plant, the following novel diterpenoids have been isolated: 11‐hydroxy‐19‐(3‐methyl‐2‐butenoyloxy)‐ and 11‐hydroxy‐19‐(3‐methylbutanoyloxy)‐5,7,9 (11), 13‐abietatetraen‐12‐one (1a/1b), 11‐hydroxy‐19‐(3‐methyl‐2‐butenoyloxy)‐ and 11‐hydroxy‐19‐(3‐methylbutanoyl‐oxy)‐7,9(11), 13‐abietatrien‐6,12‐dione (2a/2b), 6α, 11‐dihydroxy‐19‐(3‐methyl‐2‐butenoyloxy)‐ and 6α, 11 ‐dihydroxy‐19‐(3‐methylbutanoyloxy)‐7,9 (11), 13‐abieta‐trien‐12‐one (3a/3b), 11,12‐dihydroxy‐19‐(3‐methyl‐2‐butenoyloxy)‐ and 11,12‐di‐hydroxy‐19‐(3‐methylbutanoyloxy)‐8,11,13‐abietatrien‐7‐one (4a/4b), and (16R)‐17,19‐diacetoxy‐16‐hydroxy‐13β‐kauran‐3‐one (=(16R)‐17,19‐diacetoxy‐16‐hydro‐xyphyllocladan‐3‐one; 10). Compounds 2 and 3 are derivates of taxodione and taxodone, respectively, 4 is a derivative of cryptojaponol. The structure of 10 is Wised on a single‐crystal‐X‐ray analysis and CD. data.
Absolute Konfiguration von Antheraxanthin, «cis‐Antheraxantliirt» und der diastereomeren Mutatoxanthine
Authors: Märki‐Fischer Edith , Buchecker Richard , Eugster Conrad Mans , Englert Gerhard , Noack Klaus , Vecchi Max
Published: December 2004

Absolute Configuration of Antheraxanthin, ‘cis‐Aritheraxanthin’ and of the Stereoisomeric Mutatdxanthins

The assignement of structure 2 to antheraxanthin (all‐E)‐(3 S, 5 R, 6 S, 3′ R)‐5,6‐epoxy‐5,6‐dihydro‐β,β‐carotene‐3,3′‐diol and of 1 to ‘cis‐antheraxanthin’ (9Z)‐(3 S, 5 R, 6 S, 3′ R)‐5,6‐epoxy‐5,6‐dihydro‐β,β‐carotene‐3,3′‐diol is based on chemical correlation with (3 R, 3′ R)‐zeaxanthin and extensive 1H‐NMR. measurements at 400 MHz. ‘Semisynthetic antheraxanthin’ ( = ‘antheraxanthin B’) has structure 6. For the first time the so‐called ‘mutatoxanthin’, a known rearrangement product of either 1 or 2, has been separated into pure and crystalline C(8)‐epimers (epimer A of m.p. 213° and epimer B of m.p. 159°). Their structures were assigned by spectroscopical and chiroptical correlations with flavoxanthin and chrysanthemaxanthin. Epimer A is (3 S, 5 R, 8 S, 3′ R)‐5,8‐epoxy‐5,8‐dihydro‐β,β‐carotene‐3,3′‐diol (4; = (8 S)mutatoxanthin) and epimer B is (3 S, 5 R, 8 R, 3′ R)‐5,8‐epoxy‐5,8‐dihydro‐β,β‐carotene‐3,3′‐diol (3; = (8 R)‐mutatoxanthin). The carotenoids 1–4 have a widespread occurrence in plants. We also describe their separation by HPLC. techniques. CD. spectra measured at room temperature and at − 180° are presented for 1–4 and 6. Antheraxanthin (2) and (9Z)‐antheraxanthin (1) exhibit a typical conservative CD. The CD. Spectra also allow an easy differentiation of 6 from its epimer 2. The isomeric (9Z)‐antheraxanthin (1) shows the expected inversion of the CD. curve in the UV. range. The CD. spectra of the epimeric mutatoxanthins 3 and 4 (β end group) are dissimilar to those of flavoxanthin/chrysanthemaxanthin (ε end group). They allow an easy differentiation of the C (8)‐epimers.
Studies on Natural Products from Cuban Plants. Alkaloids from Tabernaemontana citrifolia
Authors: Kutney James P. , Perez Ileana
Published: December 2004

A detailed study of the alkaloids from Tabernaemontana citrifolia, a species growing in Cuba is presented. Thirteen alkaloids were isolated and characterized. One of these, (−)‐19‐oxovoacristine (7), is a new compound isolated for the first lime from a natural source.
17O‐RMN. d'éthers, de cétones et d'esters cycliques. Détermination de constante de couplage quadrupolaire
Authors: Delseth Claude , Kintzingcr Jean‐Pierre
Published: December 2004

13C‐ and 17O‐relaxation times measured in cyclic ethers, cyclic ketones, and lactones allowed the determination of the quadrupolar interaction at the O‐site. Values obtained for six‐membered rings can be used as standard values for ethers (χ = 13 MHz), ketones (χ = 10.5 MHz), and esters (χ = 11.5 MHz for dicoordinated and 9.5 MHz for monocoordinated O‐atom). Even within a series, no correlation is found between the 17O‐chemical shift and the value of quadrupolar interaction.
Reaktion von 3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirin mit 6‐Methyluracil; Kristallstruktur der Reaktionsprodukte
Authors: Dähler Marlise , Prewo Roland , Bieri Jost H. , Heimgartner Heinz
Published: December 2004

Reaction of 3‐Dimethylamino‐2,2‐dimethyl‐2H‐azirine with 6‐Methyluracil; Crystal Structure of the Products

The reaction of 3‐dimethylamino‐2,2‐dimethyl‐2H‐azirine (1) with 6‐methyl‐uracil (4) in 2‐propanol at 80° yields the 4H‐imidazoje derivative 5 as the main product. This reaction is similar to the previously reported ones with heterocyclic compounds containing the sequence NHCONHCO. In the presence of water, 5 is easily hydrolyzed to 6. The structures of 5 and 6 have been established by X‐ray crystallography.
2‐[6′‐(O‐trans‐Cinnamoyl)‐β‐D‐glucopyranosyloxy]‐3‐methyl 4H‐pyran‐4‐one, a New Acylated Pyrone Glucoside from Silene vulgaris (Caryophyllaceae) Part 186. Papers on Organic Natural Products
Authors: Borris Robert P. , Hesse Manfred , Seifert Karlheinz , Johne Siegfried
Published: December 2004

A previously unreported acylated 4‐pyroae glycoside, 2‐[6'‐(O‐trans‐cinnamoyl)β‐D‐glucopyranosyloxy]‐3‐methyl‐4 H‐pyran‐4‐one (1) has been isolated from the basic fraction of a chloroform/methanol extract of the shoots of Silene vulgaris (Moench) Garcke (Caryophyllaceae) and identified mainly on the basis of the spectral characteristics of this compound and its triacetate derivative as well as chemical degradation.
L‐Erythruronic Acid Derivatives as Building Blocks for Nucleoside Analogs. Synthesis of 4′‐C‐Aryl‐D‐ribonucleosides
Authors: Beer Dieter , Meuwly Roger , Vasella Andrea
Published: December 2004

2, 3‐O‐Cyclohexylidene‐L‐erythruronic acid (6) available in 83% yield from D‐ribonolactone (7), was treated with phenvlmagnesium bromide to give the D‐ribo and L‐lyxo derivatives 10 and 11 in high yields (Scheme 1 and 2). The diastereoselectivity depended on the temperature and mode of operation (Table 1). The absolute configuration of 10 and 11 was determined by correlation with (R)‐ and (S)phenylethanediol (17 and 16) respectively, excluding intramolecular hydride shifts during formation of 10 and 11. Reaction of 6 with methcoxymethoxyphenyllithium gave the lactones 18 and 19. The L‐lyxo isomer 19 was transformed in high yields into the D‐ribo lactone 18. Compound 10 was transformed into the adenosine analoge 24 by reduction with Diisobutylaluminium hydride, hydrolysis, acetylation and nucleoside synthesis according to Vorbrüggen (Scheme 3). Its structure was deduced from its UV., NMR. and CD. data and from those of the isopropylidene derivative 25. Similarly, 18 was transformed into the adenosine analog 29 and into the isopropylidene derivative 30.
Triaziridine. II. Erste Beispiele: 2, 3‐Dialkyl‐triaziridin‐1‐carbonsäurealkylester
Authors: Hoesch Lienhard , Leuenberger Christian , Hilpert Hans , Dreiding André S.
Published: December 2004

Triaziridines. II. First Examples: Alkyl 2,3‐Dialkyl‐triaziridine‐1‐carboxylates

The first examples of substituted triaziridines 2 are described; they carry an alkoxycarbonyl and two alkyl groups (as in 4). The preparation of these novel threemembered nitrogen homocycles was achieved by photolysis of 1‐alkoxycarbonylazimines 3c. In this way, methyl 2, 3‐(cis‐1, 3‐cyclopentylene)triaziridine‐1‐carboxylate (6a), methyl trans‐2, 3‐diisopropyl‐triaziridine‐ 1 ‐carboxylate (8a) and their ethyl ester analogues 6b and 8b were obtained in 50, 18, 65 and 21 % yield, respectively. The structure of the triaziridines 6 and 8 was deduced from their spectroscopic properties which reveal several interesting features: 1) N (2) and N (3), carrying alkyl groups, are pyramidal and invert slowly; 2) the isopropyl groups of 8 are situated trans to each other on the three‐membered ring, whereas the two alkyl groups of 6 are cis as forced by the C‐ring system; 3) N (1) is also pyramidal, despite its «amidic» nature; it inverts with an activation energy of 62 (± 4) kJ/mol; 4) the alkoxycarbonyl, group does not conjugate with N (1) and rotates rapidly.

The triaziridines 6 and 8 are thermally labile, isomerizing slowly at room temperature into the corresponding azimines 5 and 7 by cleavage of one of the bonds to N (1 ). The velocity of this ring opening reaction is almost the same for 6 and 8, so that a dependence on the relative configuration at N (2) and N (3) is not evident. The Arrhenius activation energy for the isornerization of 6a to the corresponding azimine 5a and the enthalpy difference between 6a and 5a were both determined as 100 (± 4) kJ/mol.

The photolysis of 1‐alkoxycarbonyl‐2, 3‐diisopropyl‐azimines (7) in diethyl ether was accompanied by a side reaction leading to methyl and ethyl N‐(1‐ethoxyethyl)carbamate (9a and 9b, resp.), presumably by insertion of the alkoxycarbonylnitrene, generated by photofragmentation of the azimines, into the ethereal solvent.