Synthèse de polyéthers polycycliques. 1 Stéréosélectivité de l'hétérocyclisation d'alcools tétrahydrofurfuryliques γ,δ-éthyléniques par les sels mercuriques

The intramolecular oxymercuration of the l-(2-tetrahydrofuryl)4-penten-1-ols (5) by merruric salts followed by reductive demercuration affords the 2-methyl-5-tetrahydrofuryltetrahydrofuran (9) as a mixture of cis and trans isomers in good yields. By using mercuric acetate, each isomier threo 5a and erythro 5b gives the trans isomer, 9d and 9b, respectively, as the major products. On the other hand, cyclizations carried out with mercuric chloride are not stereoselective.     

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.     

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.     

Conformation et spectrométrie de R.M.N.: II

The four isomeric 3-dimethylamino-trans-2-decalols-1,1,4,4-d₄ have been synthesised. Examination of PMR spectra of these compounds allows us to confirm the ‘flattened-chair’ conformation for the cis N(CH₃)₂^a OH^e isomer, whereas the remaining three conserve the double chair conformation. The same type of flattening is also observed in the case of the diaxial quaternary ammonium salt and is even more marked in the cis N(CH₃)₃^a OH^e isomer resulting in a ‘twist-chair’ conformation.     

Etude expérimentale et théorique de la substitution de N-méthyl-halogéno-triazoles-1,2,4 par les réactifs nucléophiles

Kinetic studies of the substitution of isomeric N-methyl-halogeno-1,2,4-triazoles with piperidine or the methoxide ion have been carried out. The experimental results show that the 1-mcthyl-5-halogcno isomer is more reactive than the 4-methvl-3-halogeno isomer. Various theoretical treatments of the reaction have been applied. The calculations show that the “frontier charge” and “delocalised bond” models give (he best results.     

Conformation et Spectrometrie de RMN. III. Spectres 13C de Diméthylamino Cyclanols et Dérivés

The ¹³C NMR spectra of 2-dimethylaminocyclohexanols and the four trans-3-dimethylamino-2-decahydronaphtols are described. The gauche interactions allow precise estimation of chemical shifts for each carbon atom; thus, band attribution can be resolved without mistake. In the case of the cis and the trans diequatorial compounds, the conformational perturbations which we have suggested before are verified by our present measurements on the substituted carbon atoms. We also show effects on adjacent atoms, which were unobservable with the usual IR and ¹H NMR techniques.     

Synthèses dans la série des constituants odorants caractéristiques de l'essence absolue de cassie (Acacia farnesiana WILLD.): Les acides méthyl-3-décène-3-oïques cis et trans,méthyl-3-décène-4-oïques cis et trans,et les quatre méthyl-3-décénols-1 correspondants

Three new fragrant compounds formerly isolated from the absolute oil of cassie (Acacia farnesiana WILLD .) have been synthesized through stereospecific reactions, and their respective structures thus confirmed. These unusual C₁₁ constituents are cis-3-methyl-dec-3-enoic acid (Ia), trans-3-methyl-dec-4-enoic acid (IIa) and cis-3-methyl-dec-3-en-1-ol (Ib). The related ‘non natural’ stereomers, namely, trans-3-methyl-dec-3-enoic acid (X) and cis-3-methyl-dec-4-enoic acid (XIX), have also been synthesized, as well as the 3-methyl-decen-1-ols IIb, XVII and XX.     

Synthesis of diazasteroids II. Synthesis of 8,11-diaza-2,3-dimethoxygona-1, 3,5 (10), 9 (11)-tetraene

Homoveratrylamine was condensed with 1-cyanocyclopentene to afford the corresponding 2-cyano-N-(3,4-dimethoxyphenethyl)cyclopentylamine (III), which was ethoxycarbonylated with ethyl chlorocarbonate to give the trans-urethan (IVt) (major product) and the cis-urethan (IVc) which could be separated through a silica gel column. The cis-urethan was converted to the trans-urethan by the action of a catalytic amount of sodium ethoxide. Based upon general considerations of nucleophilic addition such as the Michael type reaction, the physical data obtained, and the difference in ease of cyclization of the 2-aminomethyl-N-ethoxycarbonyl-. N-homoveratrylcyclopentylamines (Vt and Vc) to the corresponding cyclic ureas (Vlt and VIc), it was concluded that the major product was the trans and the minor the cis isomer. The cyclized compounds, Vlt and VIc, were subsequently submitted to the Bischler-Napieralski reaction furnishing the corresponding isoquinoline derivatives respectively. Thus the authors established a skeletal synthesis of the title compound, a 8,11-diazasteroid, and its stereochemical configuration at the C/D ring juncture was elucidated.     

Total Synthesis of (+)‐trans‐Trikentrin A

Several syntheses have already been reported for cis‐trikentrins and herbindoles, which are indole alkaloids unsubstituted at the C2 and C3 positions that bear a trans‐1,3‐dimethylcyclopentyl unit. Herein, we describe the first asymmetric and stereoselective synthesis of the more challenging trans‐trikentrin A as its naturally occurring isomer. Different approaches were investigated and the strategy of choice was a combination of an enzymatic kinetic resolution and a thallium(III)‐mediated ring contraction. The antiproliferative activities of the natural product and related intermediates have been tested against human tumor cell lines, leading to the discovery of new compounds with potent antitumor activity.     

Utilisation d'ylides du phosphore en chimie des sucres. XI. Synthèse des quatre didésoxy-3, 5-méthyl-3-pentoses parl'intermédiaire de sucres insaturés ramifiés

Treated with methylthiomethylenetriphenylphosphorane, 5-deoxy-1,2-O-iso-propylidene-β-D -threo- and -α-D -erythro-furanos-3-uloses led with good yields to a mixture of the cis-trans isomers of the corresponding methylthiovinylidenic sugars. There was no inversion of configuration at C(4) with the thero-furanosulose and a small one (7%) with its erythro isomer. These unsaturated branched-chain thio-sugars are useful synthetic intermediates. For examples, the desulfurization-hydrogenation (Raney Nickel) of each of these alkenes afforded in good yield two 3-deoxy-3-C-methyl-pentoses epimeric at C(3) and having the same configuration at C(4) as the starting alkenes. In all cases the isomer formed by attack from the less hindered face of the double bond was the preponderant one.     

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.     

Determination Rapide de la Configuration Cis Trans des Alcenes CH?CHCH? Utilisation des Complexes de Terres Rares

In Z? CH? CH?CH? Y compounds (Z or Y being an alkyl group) the ethylenic part of the spectra is often very complex and the ³J(H? C?C? H) coupling constant which is a good tool for determining the configuration, is not easily determined. We have studied such allylic derivatives and many configurations have been assigned through stereospecific synthesis. Except a very few cases, δ CH(Z) of the cis isomer is larger than δ CHZ of the trans isomer. In alcohols RCH?CH? CHOHR′ the stereoisomers behave differently in solutions with europium, praseodymium, holmium and dysprosium complexes. The spectra of the trans isomers remain strongly coupled but ³J(H? C?C? H) becomes easy to measure in the cis compounds.     

Guest‐Triggered Supramolecular Isomerism in a Pillared‐Layer Structure with Unusual Isomers of Paddle‐Wheel Secondary Building Units by Reversible Single‐Crystal‐to‐Single‐Crystal Transformation

Solvothermal reaction of Zn(NO₃)₂ ? 4 H₂O, 1,4‐bis[2‐(4‐pyridyl)ethenyl]benzene (bpeb) and 4,4′‐oxybisbenzoic acid (H₂obc) in the presence of dimethylacetamide (DMA) as one of the solvents yielded a threefold interpenetrated pillared‐layer porous coordination polymer with pcu topology, [Zn₂(bpeb)(obc)₂] ? 5 H₂O ( 1 ), which comprised an unusual isomer of the well‐known paddle‐wheel building block and the trans–trans–trans isomer of the bpeb pillar ligand. When dimethylformamide (DMF) was used instead of DMA, a supramolecular isomer [Zn₂(bpeb)(obc)₂] ? 2 DMF ? H₂O ( 2 ), with the trans–cis–trans isomer of the bpeb ligand with a slightly different variation of the paddle‐wheel repeating unit, was isolated. In MeOH, single crystals of 2 were transformed by solvent exchange in a single‐crystal‐to‐single‐crystal (SCSC) manner to yield [Zn₂(bpeb)(obc)₂] ? 2 H₂O ( 3 ), which is a polymorph of 1 . SCSC conversion of 3 to 2 was achieved by soaking 3 in DMF. Compounds 1 and 2 as well as 2 and 3 are supramolecular 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.     

Sur la composition de l'arôme de thé

A gas-chromatographic investigation of black tea aroma has revealed, besides 19 known components, the presence of 4 new substances: 1-penten-3-ol, trans-2-hexen-1-ol, α-terpineol and β-ionone. The fragmentation pattern of 1-penten-3-ol has been determined by means of high resolution mass spectrography.     

Dinuclear Tin(II) Complex of a Bulky cis‐Oxamide: Synthesis,Characterization, Crystal Structure,and DFT Studies

The reaction of the di‐lithiated oxamide of 1 with two equivalents of SnCl₂ provided the tin trans‐oxamide 3 . In solution, spectroscopic analysis suggests exclusively the formation of a trans‐oxamide (trans‐ 3 ). However, the solid state shows an atypical cis‐oxamide (cis‐ 3 ), where the oxamide fragment acts as an anti‐Janus head ligand. An ¹¹⁹Sn‐NMR variable temperature experiment ([D₈]THF) of the trans‐oxamide (trans‐ 3 ) was performed however, at lower temperature no additional signal was observed, which confirmed the absence of a dynamic equilibrium. Dispersion‐corrected density functional calculations revealed that the cis conformation of this tin(II) oxamide complex is more stable than the trans isomer by 1.4 kcal · mol^–1.     

Etude Quantitative de la Reactivite–XXI: Comportement sous l'Impact Electronique de Bromures de Cyclopentyle et Cyclohexyle α-substitutes cis et trans

Mass spectra of ten pairs of cis and trans 2-substituted cyclopentyl and cyclohexyl bromides were recorded for eleven separate energies located between 10 and 20 eV. For each isomer, a calculation of the mass spectrum and of its variations with electronic voltage from the quasi-equilibrium theory, allowed us to determine the activation energies of the main [M – Br] fragmentation. These numeric data show that the observed differences between the mass spectra of diastereoisomers essentially depend on: (1) the enthalpy difference between isomeric molecular ions in their ground states for fluorine and oxygen substituted compounds and (2) the enthalpy difference between the isomeric transition states of the [M – Br] cleavage for chlorinated and brominated compounds. In the latter case, this can be explained by the halide participation in the expulsion of the bromine substituent from the trans isomers.     

Détermination de la configuration de glycosylaziridines par dichroïsme circulaire. Note de laboratoire

CD.-Based Configurational Assignments of Glycosylaziridines The relationship between CD.-curves and the configuration of the trans-2-benzoyl-3-phenylaziridines was known. By studying a series of cis- and trans-2-glycosyl-3-benzoylaziridines we have shown that CD. allows the assignment of the configuration at both asymetric C-atoms. As benzoylaziridines can easily be obtained from cyano- or alkoxycarbonylaziridines without configurational change, the absolute configuration of these last two classes of compounds can also be assessed by this method.     

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.     

A short and efficient synthesis of 4a-substituted cis-hexahydro-1,2,3,4,4a,9a-carbazol-4-ones

Photocyclization of tertiary aryl enaminones 1 gave trans-hexahydrocarbazol-4-ones 2 which were subsequently alkylated with a series of electrophiles via the corresponding thermodynamic anion. The 4a-substituted derivatives formed were shown to have the cis-hexahydrocarbazol-4-one structure by comparison with the previously prepared trans isomer.