Sur les constituants odorants de l'essence absolue de Cassie (Acacia farnesiana WILLD.)

The absolute oil of cassie (Acacia farnesiana WILLD. ) has been thoroughly investigated by using several combined chromatographic techniques. Among the 38 new constituents which were thus identified in this oil, four deserve a particular mention, namely, the cis-3-methyldec-3-en-1-ol (I), the related acid III, the trans-3-methyl-dec-4-enoic acid (IV), and the homoterpene lactone dihydroactinidiolide (II). With the exception of the last one, these unusual C₁₁ compounds play a prominent role in the characteristic fragrance of cassie oil.     

Synthèse de céphalosporine-lactones

Condensation of azetidinones 2a and 2b with mercaptan 3 gave respectively compound 10 or a 1:1 mixture of 17 and 17 ′. Bromination of 10 , afforded cis and trans-bromohydrins 13a and of 17 and 17 ′ cis and trans-bromohydrins 18a . Acetylation and reduction with zinc and acetic acid of these bromohydrins gave cephems 4a or 4b and 4b ′ respectively.     

Polymérisation radicalaire du pentadiène-1,3. II. Microstructure des résidus pentadiéniques dans les homo- et copolymères des cis et trans pentadiènes-1,3 avec l'acrylonitrile

The microstructure of diene units was investigated in radical homopolymers of the cis and trans isomers of 1,3-pentadiene and copolymers with acrylonitrile, synthetized in bulk and emulsion. Experiments were carried out by infrared spectroscopy, 100 MHz ¹H-NMR, and 25 MHz ¹³C-NMR studies. No difference between the bulk and emulsion samples was noted. The microstructure of poly(1,3-pentadiene) is practically independent of the cis or trans configuration of the diene monomer and is as follows: 56–59% trans-1,4, 15–17% cis-1,4, 16–20% trans-1,2 7–10% cis-1,2 and 0% 3,4. On the other hand, up to about 30% of incorporated acrylonitrile (10% in the feed), the microstructure of the pentadiene fraction in the copolymers is not affected. This finding suggests that the penultimate unit has very little influence on the polymerization process involving the terminal pentadienly unit. Beyond 10% of acrylonitrile in the feed, the proportions of the structural units were linearly dependent upon the acrylonitrile content: trans-1,4 content increased whereas the amounts of cis-1,4 trans-1,2 and cis-1,2 decreased (except the cis-1,2 fraction, constant in the copolymers from the cis-diene). These results are discussed on the assumption that the microstructure of pentadiene residues is strongly associated with the acrylonitrile comonomer in the feed.     

Interactions intramoléculaires. XXVI—Constantes de couplage et hétérogénéités conformationnelles dans une série de R-3 et R-5 cyano-4 cyclohexènes deutériés (R=méthyl ou t-butyl)

For trans-3-R- and 5-R-1-acetoxy-4-cyanocyclohexene-6,6-d₂ the molar fractions of diequatorial conformers are 0.83 (3-methyl), 0.68 (5-methyl), 0.57 (3-tert-butyl) and 0.55–0.69 (5-tert-butyl). For the last two compounds the values of the coupling constants are in agreement with the hypothesis of an ee?aa equilibrium. For the cis isomers, the molar fractions of equatorial alkyl conformers are 0.76 (3-methyl and 5-methyl) and 1.0 (3-tert-butyl and 5-tert-butyl). The cis-1-acetoxy-3-tert-butyl-4-methoxycarbonyl-cyclohexene presents a conformational heterogeneity. The conformational free energy of the methyl group in position 4 has been evaluated as ?0.6 kcal mol^?1 (2.5 kJ mol^?1).     

Le diméthyl- et le diéthyl-tétracarbonylosmium Synthèse et réactivité

The sodium salt Na₂[Os(CO)₄] has been obtained in high yields by the reduction of either OsH₂(CO)₄ or Os₃(CO)₁₂ with sodium sand in the presence of catalytic amounts of 2, 2′-bipyridyle. The reaction of Na₂[Os(CO)₄] with alkylating agents such as methyl and ethyl iodide produces OsR₂(CO)₄ (R = CH₃, C₂H₅). NMR. and IR. spectra indicate a cis-octahedral structure of symmetry C_2v for these new alkyl compounds. Bromine breaks one osmium-carbon bond in cis-Os(CH₃)₂(CO)₄ to give cis-OsCH₃Br(CO)₄, whereas in cis-Os(C₂H₅)₂(CO)₄ both ethyl groups are easily displaced by bromine to give cis-OsBr₂(CO)₄. Under CO pressure and at elevated temperature cis-Os(CH₃)₂(CO)₄ is converted to Os(CO)₅ and ethane. With cis-Os(C₂H₅)₂(CO)₄ two CO are inserted in osmium-carbon bonds to give . NMR. and IR. data suggest a cis-configuration for this derivative and the possibility of the presence of rotational isomers.     

Interactions intramoleculaires. XXI—Constantes de couplage et interactions gauches avec un groupement t-butyle (molécules cyclohexaniques deutériées)

Different isotopic modifications of deuterated products of 1-t-butlyl-4-methoxycarbonyl cyclohexene (d₄-3,3,6,6), cis- and trans-3-methyl-4-cyanocyclohexene (d₃-3,6,6), cis- and trans-3-methyl-4-cyanocyclohexene (d₃,6,6), cis- and trans-3-t-butyl-4-methoxycarbonylcyclohexene (d₃,-3,6,6) are shown by nuclear magnetic resonance spectral analysis. By comparison of ³J and ⁴J coupling constants of model molecules and molecules with large gauche interactions, we obtain proof that the latter are in a chair conformation with moderate cycle deformations.     

Etude par spectrométrie de masse des cyclopenténols,cyclopentène-diols-3,4 et cyclopentène-triols-3,4,5

The mass spectra of cyclopentene-1-ol-3, -1-o1-4, those of cis- and trans-cyclopentene-3,4-diol and of the three stereoisomers of cyclopentene-3,4,5-triol have been studied. Decomposition modes based upon results obtained using deuterium labelled analogues are discussed.     

Mécanisme de solvolyse des cis- et trans-(p-toluènesulfonates) d'aryl-2-cyclopentyle I. Etude de la première étape de la solvolyse: effets isotopiques de l' atone de deutérium en position 2, effets de sel basique et effet spécial de sel

Solvolysis Mechanism of cis - and trans-2-Arylcylopentyl p-Toluenesulfonates. The Step: 1-Deuterium Isotope Effects, Basic Salt Effects, and Special Salt Effect We have studied the first step of the solvolysis of cis and trans-2-arylcyclopentyl p-toluenesulfonates in HCOOH, AcOH, and EtOh. All substrates show a high kinetic 1-deuterium isotope effect (k_H/k_D(1) >1.15). This fact indicates that first step leads to classical intimate ion-pair Which dissociates to a solvet-separated ion-pair, without participation either of solvent, the 2-aryl group, or a H-atom at C(2). The slight influence of added basic ions on reaction rate allows us to exclude any direct solvent attack on the covalent substrate even in the most favorable case, i.e. ethanolysis of 2-(p-nitrophenyl)cylopentyl-p-toluenesulfonates. Furthermore, solvent-separated ion pair formation is indicated by the special salt effect induced by LiClO₄.     

Etude en Spectrométrie de Masse. IX—Fragmentation de Cyclopropanes Dicarboxylate de Méthyle-1,2 cis et trans Diversement Substitués,et des Homologues Cyclobutaniques,Cyclopentaniques et Cyclohexaniques non Substitués

A mass spectral study of cis- and trans-decarboxymethylcyclopropanes substituted on C-1, C-2, C-3 reveals that they show the same behaviour under electron impact. In every case, breaking of the carbocyclic ring is the first step giving the most important peaks. By comparing unsubstituted diesters of cyclopropane with those of the cyclobutane, cyclopentane and cyclohexane homologues, we have analysed the transmission of electronic effects by the different rings.     

Synthèse de l'amino-4 formyl-3 méthyl-6 pyridazine

The 4-amino-3-formyl-6-methylpyridazine, a new reagent in the pyridazine series, has been synthesized by two different routes. For that purpose some new ortho-substituted compounds of pyridazine have also been prepared.     

Interactions intramoléculaires. XXVII—Etudes structurales en série bicyclo[4.1.0]heptanique (effets d'anisotropie sur les déplacements chimiques du proton; constantes de couplage et équilibres conformationnels)

All the ¹H n.m.r. parameters of the following derivatives of 1,6-dimethylbicyclo[4.1.0]heptane are determined: 3,4-dimethoxycarbonyl (3 diastereoisomers), cis- and trans-3-methoxycarbonyl-2,2,5,5-d₄, cis- and trans-3-methyl-3-methoxycarbonyl; the cis- and trans-1,5,5-trimethylbicyclo[4.1.0]-3-heptanols are studied in the same way. The different chemical shifts are correlated with the aid of a collection of empiral increments. The conformational equilibria are determined from the vicinal coupling constants; the conformational free energies of the COOCH₃ group are evaluated; the part played by gauche interactions is considered.     

Interactions intramoléculaires: XXIII—Constantes de couplage et interactions gauches avec un groupement t-butyle (cyclohexanones disubstituées 3, 4)

The ¹H NMR spectra of a series of cis and trans-3R,4 X-cyclohexanones (-2,2,6,6-d₄) are analysed. By comparison of their ³J coupling constants with those of cyclohexane homologues we obtain information about the chair–chair equilibrium constants for R = CH₃, X = CN, the chair structure of cis isomers with an equatorial t-butyl group, and a conformational heterogeneity with trans (CH₃)₃C and CN groups. This latter situation is analysed by means of a simplified but controlled Karplus relationship, on the basis of a mixture of two conformers; this involves a diequatorial chair and a boat form with a dihedral angle Φ₃₄ of about ?6°.     

La configuration du «carquéjol» (Isopropényl-2-méthylène-3-cyclohexène-4-ol) et la conformation privilégiée de l' ortho-néo-isomenthol

The complete stereochemistry of carquejol (= cis-(2S)-isopropenyl-3-methylene-cyclohex-4-en-1-ol) is described. The absolute configuration was obtained from the circular dichroism of the corresponding 0-menthones. Carquejol and its reduction products, having the all-cis configuration, appear from NMR. measurements to prefer a conformation having the hydroxyl (or acetoxyl) group axial and the isopropenyl (or isopropyl) group equatorial, even when the exo-methylene group is reduced to methyl. The mass spectra of the compounds are briefly described.     

Highly Efficient Deep‐Blue Emitters Based on cis and trans N‐Heterocyclic Carbene PtII Acetylide Complexes: Synthesis,Photophysical Properties,and Mechanistic Studies

We have synthesized cis and trans N‐heterocyclic carbene (NHC) platinum(II) complexes bearing σ‐alkynyl ancillary ligands, namely [Pt(dbim)₂(C?CR)₂] [DBIM=N,N′‐didodecylbenzimidazoline‐2‐ylidene; R=C₆H₄F ( 4 ), C₆H₅ ( 5 ), C₆H₂(OMe)₃ ( 6 ), C₄H₃S ( 7 ), and C₆H₄C?CC₆H₅ ( 8 )] and [Pt(ibim)₂(C?CC₆H₅)₂] ( 9 ) (ibim=N,N′‐diisopropylbenzimidazoline‐2‐ylidene), starting from [Pt(cod)(C?CR)₂] (COD=cyclooctadiene) and 2 equivalents of [dbimH]Br ([ibimH]Br for complexes 9 ) in the presence of tBuOK and THF. Mechanistic investigations aimed at uncovering the cis to trans isomerization reaction have been performed on the representative cis complex 5 a [Pt(dbim)₂(C?CC₆H₅)₂] and revealed the isomerization to progress smoothly in good yield when 5 a was treated with catalytic amounts of [Pt(cod)(C?CR)₂] at 75 °C in THF or when 5 a was heated at 200 °C in the solid state under an inert atmosphere. Detailed examination of the reactions points to the possible involvement, in a catalytic fashion, of a solvent‐stabilized Pt^II dialkyne complex in the former case and a Pt⁰ NHC complex in the latter case, for the transformation of the cis isomer to the corresponding trans complex. Thermal stability and the isomerization process in the solid state have been further investigated on the basis of TGA and DSC measurements. X‐ray diffraction studies have been carried out to confirm the solid‐state structures of 4 b , 5 a , 5 b , and 9 b . All of the synthesized dialkyne complexes 4 – 9 exhibit phosphorescence in solution, in the solid state at room temperature (RT), and also in frozen solvent glasses at 77 K. The emission wavelengths and quantum yields have been found to be highly tunable as a function of the alkynyl ligand. In particular, the trans isomer of complex 9 in a spin‐coated film (10 wt % in poly(methyl methacrylate), PMMA) exhibits a high phosphorescence quantum yield of 80 %, which is the highest reported for Pt^II‐based deep‐blue emitters. Experimental observations and time‐dependent density functional theory (TD‐DFT) calculations are strongly indicative of the emission being mainly governed by metal‐perturbed interligand (³IL) charge transfer.     

On the Effect of Tether Composition on cis/trans Selectivity in Intramolecular Diels–Alder Reactions

Intramolecular Diels–Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6‐31+G(d) and CBS‐QB3 levels of theory for a series of 1,3,8‐nonatrienes, H₂C?CH? CH?CH? CH₂? X? Z? CH?CH₂ [? X? Z? =? CH₂? CH₂? ( 1 ); ? O? C(?O)? ( 2 ); ? CH₂? C(?O)? ( 3 ); ? O? CH₂? ( 4 ); ? NH? C(?O)? ( 5 ); ? S? C(?O)? ( 6 ); ? O? C(?S)? ( 7 ); ? NH? C(?S)? ( 8 ); ? S? C(?S)? ( 9 )]. For each system studied ( 1 – 9 ), cis‐ and trans‐TS isomers, corresponding, respectively, to endo‐ and exo‐positioning of the ? C? X? Z? tether with respect to the diene, have been located and their relative energies (E_rel^TS) employed to predict the cis/trans IMDA product ratio. Although the E_rel^TS values are modest (typically <3 kJ mol^?1), they follow a clear and systematic trend. Specifically, as the electronegativity of the tether group X is reduced (X?O→NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis‐TS, namely (1) unfavorable torsional (eclipsing) strain about the C4? C5 bond, that is caused by the ? C? X? C(?Y)? group’s strong tendency to maintain local planarity; and (2) attractive electrostatic and secondary orbital interactions between the endo‐(thio)carbonyl group, C?Y, and the diene. The former interaction predominates when X is weakly electronegative (X?N, S), while the latter is dominant when X is more strongly electronegative (X?O), or a methylene group (X?CH₂) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1 , 2 , 3 , and 4 (published work) and 5 , 6 , and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans‐selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14 , which undergoes a more trans‐selective IMDA reaction than the corresponding ester tethered precursor 13 .     

Mécanisme de solvolyse des cis - et trans-(p-toluénesulfonates) d'aryl1-2-cyclopentyle II. Etude des étapes ultérieures à l'ionisation lors de la solvolyse des cis-(p-toluénesulfonates) d'aryl-2-cyclopentyle

Solvolysis Mechanism of cis- and trans-2-Arylylopentylp- Toluenesulfonates, Subsequent Step in cis-2-Arylcyclopentyl p-Toluenesulfonate Solvolysis The solvolysis of a series of 1-deuteriated, 2-deuteriated, and undeuteriated cis-2-arylcyclopentyl p-toluenesulfonates in HCOOH, AcOH, and EtOH has been studied. We have shown that classical secondary carbocation arising from substrate ionisation undergoes two concurrent processes, namely k_c (direct products formation) and k_ip (hydrogenium bridged ion formation as tertiary carbocation or products precursor). The intrinsic properties of solvent and the aryl substitutant electronic effects the total solvolysis rate and the respective contributions of k _c and k _ip processes. Comparing the observed and calculated kinetic isotope of D–C(2) allows one to conclude that no step can called ‘rate-determining step’ but that the steps following ionisation have a preponderent effect on the total solovolysis rate.     

Polymérisation anionique des diènes. VI. Microstructure des polybutadiène et polyisoprène par résonance magnétique protonique à 250 MHz et mécanismes de propagation

Analysis by 250-MHz proton magnetic resonance (PMR) allows more precise examination of the microstructure of anionic polyisoprenes and polybutadienes obtained in the presence of organo-alkali metals. Besides vinyl addition, the propagation of contact ion pairs in dioxane solvent gives a mixture of cis and trans products with isoprene, whereas only trans product is obtained with butadiene. The presence of 1,4-trans-polyisoprene appears to be inconsistent with the cis configuration of the polyisoprenyllithium living end in dioxane or tetrahydrofurane media. In taking into account the existence of complexation phenomena, it was suggested that propagation mechanisms should involve a transition state which should begin with the trans configuration before isomerization into the more stable cis configuration. For the free ions, the living end of the carbanion should be entirely trans.     

Identification of cis/trans isomers of methyl ester and oxazoline derivatives of unsaturated fatty acids using GC–FTIR–MS

Identification of cis/trans isomers of unsaturated fatty acids cannot usually be achieved by GC-MS (gas chromatography-mass spectrometry) without reference substances. In this study a GC-FTIR-MS system (gas chromatography-Fourier transform-mass spectrometry) was used to identify fatty acid methyl esters (FAMEs) and differentiate between the cis/trans isomers. Besides methyl esters, 2-alkenyl-4,4-dimethyloxazoline derivatives (DMOX), which have been used to locate double bond positions of unsaturated fatty acids, were examined with respect to their suitability for cis/trans differentiation. A combined GC-FTIR-MS system with a wide band (4000–550 cm^?1) mercury cadmium telluride (MCT) detector was used in series and parallel to identify 31 reference unsaturated fatty acids, including 7 pairs of cis/trans isomers. Serum samples of healthy persons and commercially available fish oil were analyzed as examples of complex mixtures. Using splitless injection the detection limit for the less sensitive IR detector was 25 ng/μl in case of the weak cis and trans bands. In the FTIR spectra cis/trans isomers were identified by analysis of bands arising from C? H out-of-plane (oop) bending: for both the FAME and DMOX derivatives cis-1,2-disubstituted double bonds give a strong band near 720 cm^?1 and the corresponding trans isomers near 967 cm^?1. cis Isomers could be identified further by a band at 3012 cm^?1. With the combined data of the GC-FTIR-MS system it is now possible to identify polyunsaturated fatty acids with regard to the discrimination of cis/trans isomers.     

Etude Stéréochimique par RMN 1H de Tetrahydropyrannes β-Chlorés α-Substitués

The ¹H NMR study of 2-alkyl-3-chlorotetrahydropyrans, obtained by reaction of Grignard reagents with a mixture of cis/trans-2,3-dichlorotetrahydropyrans, shows cis/trans configuration of two isomers in which the alkyl substituents are exclusively in the equatorial position. 3-Chloro-2-phenyltetrahydropyran exists in trans (eq-eq) configuration only. The ¹H NMR study of cis/trans 2-alkoxy (or aryloxy)-3-chlorotetrahydropyrans, obtained by reaction of alcohols or phenol with 2,3-dichlorotetrahydropyrans, shows the axial position of the alkoxy (or aryloxy) substituent.     

Structures cristallines et moléculaires des muses macrocycliques. II. La trans-civettone et sa 2,4-dinitrophénylhydrazone

Crystal and Molecular Structure of Macrocyclic MUSKS. II. trans-Civetone and its 2, 4-Dinitrophenylhydrazone The trans and cis isomers of civetone (C₁₇H₃₀O) crystallize in isomorphous systems and form plastic crystals (tetragonal, space group I4₁ a=9.95 (4), c = 32.79 (1) Å, Z = 8). Mixed crystals were prepared with cis-civetone as second component. Accordingly the diffuse structural model obtained for the disordered phase of the cis-isomer [1] is also regarded as representative of that of trans-civetone. The crystal structure of trans-civetone 2,4-dinitrophenylhydrazone (DNPHTC; C₂₃H₃₄N₄, Monoclinic, Space group P2₁/c, a=8.364(2), b=7.971(1), c=36.025(8) Å, β=91.44 (2)°) was solved by direct methods and refined to a final R of 0.09 (R_w = 0.021). The macrocycle adopts a sexangular conformation [23*434*44*], and its mean plane is approximatively perpendicular to that of the aromatic substituent. Empirical force field calculations have shown that the DNPH substituent has very little influence on the macrocycle conformation. The intermolecular interactions take place essentially between groups of the same type: macrocycle…macrocycle and DNPH…DNPH.