Action du fluorure de potassium sur les tosylates α-fluores: Synthese et proprietes de derives 1,2-difluores.

Fluorinated alcohols, synthesised from epoxides by action of trimethylamine fluorhydrate, can be transformed to 1,2-fluorotosylates when they are treated with tosyl chloride in pyridine. The physico-chemical propreties of these fluorotosylates are studied. The action of KF, in diethylen glycol, on these α-fluorinated tosylates gives the corresponding 1,2-difluorinated compounds in good yield. The stereochemical course of the last reaction can be elucidated from an analysis of the ¹⁹F NMR of the 1,2-difluorocyclohexane.     

Effet du benzene dans la reaction de grignard sur les cetones encombrees

The substitution of Benzene or Toluene to ether in the Grignard reaction with hindered ketones leads to a 75% increase of yield.     

Activation anionique du phosphite de diethyle par le fluorure de potassium depose sur alumine,synthese de phosphonates fonctionalises

Dry reactions of diethylphosphite on KF-Al₂O₃ with different. electrophiles conduct to the synthesis of functionalized phosphonates.     

Extension de la reaction de Wittig: Condensation “d'ylures enolates” sur les cetones aliphatiques

The enolate ylide Ph₃P⁺C^?C(Ph)O^?Li₊ obtained by the reaction of HMPT-Li with the benzoylmethylenetriphenylphosphorane Ph₃PCHCOPh reacts with aliphatic ketones, in contrast to its precursor. This condensation makes it possible to prepare β,γ-unsaturated ketones, of type RCHC(R′)CH₂COPh, instead of the α,β isomer usually obtained in a Wittig reaction.     

Etude de l''influence du diluant hydrocarbone dans la reaction des organomagnesiens primaires sur les cetones encombrees

Primary alkylmagnesium bromides are prepared in hydrocarbon solutions such as benzene or toluene using 1 equivalent of diethyl ether or tetrahydrofuran. Their reactions with diisopropylketone and cyclohexylisopropylketone increase drastically the addition products in comparison with the reactions in diethyl ether or in tetrahydrofuran. No important differences were found in the distribution of reaction products between diethylether or tetrahydrofuran and between benzene and toluene when they are used as complexant and diluent respectively.     

Condensations aryniques d'enolates de cetones—VII: Synthese generale de benzocyclenones non substituees; Mecanisme de condensation du benzyne sur les enolates de cetones

Some 1,2-benzocyclene-3 ones, so far, unknown have been prepared easily by condensation of the benzyne on the enolates of cyclanones. The general mechanism of the condensation of the benzyne on the enolates of alicyclic ketones in aprotic medium is proposed.     

Addition des thiols sur les cetones—II : Mecanisme de l'addition du propanethiol

Addition of propanethiol to cyclohexanone in aqueous ethanol involves two consecutive steps, both of them rate limiting. The first step is the addition of the thiol to the conjugate acid of the ketone, giving an instable intermediate hemithioketal. Another thiol molecule adds to this, giving the thioketal. From the rate expression the thiol addition rate constant to the cyclohexanone was calculated.     

Etude de la réactivité du fluorure de potassium sur des esters polyhalogénés

Reactions of polyhalogenated esters with potassium fluoride in polar solvents have been studied. Two kinds of reactions are possible depending on the starting compound: the hydrochlorinated estersRCCl₂CH₂CHR′CO₂CH₃ (R=Cl, -CF₃ ; R′=H, -CH₃ give the corresponding α-β unsaturated derivatives. Moreover when using ethylene glycol as a solvent, a transesterification reaction occurs after the dehydrohalogenation. From perhalogenated esters, mainly decarboxylation products are formed; for example in DMSO as a solvent, the fluorination of the telomers Cl-(CFClCF₂)_n-CO₂CH₃ yields the corresponding perfluoroalkenes C_2nF_4n. Some mechanistic interpretations are given in order to explain the formation of the different compounds.     

Addition du chloracetate de methyle sur les olefines

α-Chloroesters add to olefins or dienes under redox catalysis by cuprous chloride in the presence of Bipy or Phen, leading to γ-chloroesters or unsaturated esters.     

Action des homocuprates sur les cetones α,α′-dibromees. Une nouvelle methode de synthese de cetones encombrees

The reaction between alkyllithium homocuprates and α,α′-dibromoketones permits the monoalkylation of ketones after hydrolysis of the reaction intermediate; the latter reacts with an excess of alkyl halide and gives the dialkylated product. Four alkylation reactions (methylation, ethylation, isopropylation and t-butylation) of α,α′-dibromoketones have been studied. While monoalkylation leads to secondary/primary and tertiary/secondary ketones from bis-primary and bis-secondary structures, dialkylation permits the synthesis of bis-secondary and bis-tertiary ketones. The introduction of two tertiary groups in the same structure is nevertheless impossible.     

Action des homocuprates sur les cetones α-bromees. Une nouvelle methode d'alcoylation de cetones

The reaction between an alkyllithium homocuprate and an α-bromoketone yields the corresponding alkylated ketone. This alkylation method allows the regiospecific introduction of a primary, secondary, or a tertiary alkyl group on the ketone at the site initially brominated. Two concomitant mechanisms, halogen-metal exchange and nucleophilic substitution, explain this new reaction. While these two mechanisms co-exist in substitution by primary and secondary alkyl groups, only nucleophilic substitution seems possible in the case of tertiary alkyl groups.     

Influnce des interactions de torsion dans la reduction des cetones par les hydrures interpretation generale du deroulement sterique de la reduction des cetones acycliques et de l'addition des organomagnesiens sur les aldehydes acycliques

Reduction of ketones L-CHMe-CO-R [L=Ph and Cy(Cy = cyclohexyl) and R=Me, Et, iPr and tBu] affords pairs of diastereoisomeric alcohols L-CHMe-CHOH-R. The predominant diastereoisomer is always that predicted by Cram's rule, and the stereoselectivity of the reaction generally increases as R is made more bulky. Thus, with LiAlH₄ in ether at 35°, the diastereoisomer ratios are respectively 2.8:1, 3.2:1, 5.0:1, and 49:1 when L=Ph and 1.6:1, 2.0:1, 4.1:1, and 1.6:1 when L=Cy. With NaBH₄ in isopropanol at 50°, these ratios are respectively 1.6:1, 2.0:1, 2.7:1, and 7.3:1 when L=Ph, and 1.2:1, 1.6:1, 3.2:1, and 3.5:1 when L=Cy. It is suggested that an important factor determining the steric course of the reduction of both open-chain ketones and cyclohexanones is torsional strain in the transition state, and that torsional strain involving partial bonds can represent a substantial fraction of the strain between fully-formed bonds, even when the degree of bonding is quite low. This postulate has been made the basis of an internally consistent interpretation of the steric course of the reaction between carbonyl compounds and nucleophilic reagents such as hydrides and Grignard reagents.     

Extension de la reaction de wittig—II : Condensation “d'ylures enolates” sur les cetones aliphatiques α,β-insaturees

The enolate ylide Ph₃P⁺-C^?=C(Ph)O^?Li⁺, obtained by reaction of HMPT-Li with the benzoylmethylenetriphenylphosphorane Ph₃P=CH-CO-Ph, reacts with aliphatic α,β-unsaturated ketones. The betaïne obtained by Michael-type addition gives a substituted cyclohexenone by intramolecular ketolisation.     

Effets de temperature sur les modes normaux du monocristal de nitrate de strontium

Raman spectra investigation of SrNO₃ single crystals cut in two different orientations allows an unambiguously determination of Raman modes symmetry species. The two hypothesis of the crystal structure are discussed, the factor group T_h allowing a better interpretation of experimental data than the factor group T.A systematic temperature study of Raman bands (frequencies, broadness, integrated intensities) conducts to the separation of internal and external modes and shows a singularity in the 173–183° K temperature region.     

Influence de l'oxygène sur la conductivité électrique du fluorure de baryum monocristallin

The influence of oxygen on the electrical properties of single crystals of BaF₂ was investigated in the temperature range 450–1150°C. Two types of studies have been undertaken: total ac conductivity and cation transport measurements. The results confirm an anion Frenkel disorder model in MeF₂. Substitution of the fluorine atoms by oxygen in the lattice supposes the creation of the vacancies V^·_F. The evaluation of intrinsic, extrinsic and association domains as a function of oxygen partial pressure has been studied. Values for the energy of formation of the intrinsic defects, the motion energies of V^·_F-vacancies and association or precipitation energy have been deduced from the slopes of the conductivity curves.     

Synthese de cetones aliphatiques encombrees : Action des organolithiens sur les dimethyl-4,4 oxazolines-2. Addition des organometalliques sur les sels de dimethyl-4,4 oxazolinium-2

α,α-Disubstituted ketones result from the reaction of organolithium compounds with substituted 4,4-dimethyl-2-oxazolines, 4, after hydrolysis of the intermediate enamine. Alkylation of the latter also permits the synthesis of α,α,α-trisubstituted ketones. α,α-Disubstituted ketones have been prepared by addition of organometallic reagents to 4,4-dimethyl-2-oxazolinium salts, 6. The efficiency of this method has been compared to that of other currently used methods.     

Condensation des bromures de perfluoro-alkylmagnesium sur les aldehydes et cetone α-halogenes

Perfluoroalkyl magnesium halides react with α halogenocarbonyl compounds producing diastereoisomeric halohydrines which lead to perfluoroalkyl epoxydes by cyclisation.NMR study shows that the epoxyde configuration may be deduced from the coupling constant value ⁴J(H-F) between the epoxyde proton and the R_F radical.The condensation on the carbonyl group is less stereo-selective with R_FMgX than with usual Grignard reagents.