Sur la reactivite des organomagnesiens derivant de l'addition d'organomagnesiens allyliques sur l'isoprene

Contrary to a recent report, it is shown that allylic Grignard reagents prepared by treating allylic Grignard reagents with isoprene and a catalytic amount of Cp₂TiCl₂ react normally with carbon dioxide and carbonyl compounds: a complete allylic rearrangement is observed.     

Alcoylation par l'iodure de butyle,de l'enolate de tetrabutylammonium de l'acetylacetone; nature de l'entite reagissante

The alkylation of tetrabutylammonium acetylacetonate with butyl iodide was studied in order to specify the nature of the reactive anionic species during the nucleophilic reaction of an ambident anion, under similar conditions to those of phase transfer catalysis. The C/O alkylation ratio changes with neither the solvents nor the enolate concentration; however k_obs, varies with the solvent but does not depend on the énolate concentration. The results and spectrophotometric UV data show that only one reactive species, the ion-pair, is involved.     

Diastereoselectivite induite lors de l'addition des organomagnesiens sur les diacyl-1,1′ferrocenes

The reaction of Grignard reagents with 1,1′-diacylferrocenes proceeds with a pronounced stereoselectivity. This is demonstrated by experiments in which the nature of the reagent and the acyl groups are varied. In general, additions of ethyl, phenyl, cyclohexyl and benzylmagnesium halides to diacetylferrocene (I) afford preferentially the erythro-diols (III) whereas the threo-diastoreomers (IV) can be obtained by treatment of the corresponding ketones (IIa—IId) with methylmagnesium bromide. This stereoselectivity results from a preferential direction of attack by the Grignard reagent relative to the intermediate hydroxyketone. The same ratio of isomers is obtained if the reaction is performed on the corresponding hydroxyketone.     

Alkylation de terpenes en deux etapes par ene-reaction

A simple, two-step homologation of terpenes is reported that requires ene-reaction with PhSO₂NSO and subsequent alkylation of the intermediate adducts with Cu¹ catalyzed Grignard reagents.     

Synthese en serie encombree. preparation de l'acide ditertiobutyl-methylacetique-tBu2 MeCCOOH et de quelques composes cetoniques derives de cette structure

The synthesis of ^tBU₂MeCCOOH, which is among the most sterically hindered known acjds is described. Only Newman's sequence via ^tBU₂CO, ^tBu₂MeCOH, ^tBu₂CCH₂, _tBu₂CHCH₂OH, ^tBu₂CHCOOH, ^tBU₂CHCOCI and ^tBu₂CCO, which has been optimized in this work by a direct access to ^tBu₂CHCOOH, permits the preparation of ^tBu₂MeCCOOH. The condensation of the corresponding chloride with a Grignard reagent yields new highly-hindered ketones ^tBu₂MeCCOR which by alkylation give more substituted structures. The limitations of each method have been studied in this work.     

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.     

Etude de l'action des alkylmagnesiens primaires et arylmagnesiens sur les anhydrides tricycliques pontes

The reaction of primary alkyl and aromatic Grignard reagents with bridged tricyclic di-carboxylic anhydrides gives the corresponding dialkylated tricyclic lactones via di-addition process. The lactones were transformed by retro-Diels-Alder reactions into 4,4-dialkylated butenolides.     

Transposition eventuelle lors de l'action de bromures β-ethyleniques CH2CHCH(R)CH2Br (R = CHCH2, C2H5, C6H5) sur le magnesium

Reaction betweenβ-ethylenic bromides CH₂CHCH(R)CH₂2Br and magnesium in ether has been studied. With R = CHCH₂, it gives rise both to normal and rearranged Grignard reagents. With R = C₂H₅ and C₆H₅, only the normal Grignard reagent is formed.     

Etude cinetique de la copolymerisation alternee de l'indene et du methacrylate de methyle en presence de sesquichlorure d'ethylaluminium

The copolymerization of indene with methyl methacrylate (MAM) initiated by u.v. irradiation, in the presence of ethylaluminium sesquichloride (SCEA) as a complexing agent, yields alternating copolymers when [Indene] ≥ [MAM] ≥ [SCEA]. Values of $\text{M}$_n of the copolymers range from 32,000 to 900,000, depending on the concentrations of the reagents, reaction temperature and intensity of u.v. light. The kinetics can be explained simply by assuming a statistical copolymerization of indene with a MAM-SCEA binary complex, but intervention of a ternary complex SCEA-MAM-indene cannot be discarded. At high MAM concentrations, the free MAM becomes involved in the copolymerization.     

Alkylation des carbenoides par des nucleophiles. : II. Substitution nucleophile de l'halogene de carbenoides α phosphonates catalysee par le cuivre(I)

The addition of a catalytic amount (12%) of a copper(I) salt to a mixture of an α-lithio-α-chloroalkylphosphonate and an alkyllithium RLi or a Grignard reagent RMgX leads to the formation of a new organometallic reagent in which the R group has replaced the chlorine atom of the carbenoid. This nucleophilic alkylation of carbenoids can be performed with secondary-alkyl Grignard reagents, and with aryllithium, alkenyllithium and alkynyllithium reagents in good yields (60–80%).     

Highly efficient alkylation to ketones and aldimines with Grignard reagents catalyzed by zinc(II) chloride

A highly efficient alkylation to ketones and aldimines with Grignard reagents in the presence of catalytic trialkylzinc(II) ate complexes derived from ZnCl2 (10 mol %) in situ was developed. This simple Zn(II)-catalyzed alkylation could minimize the well-known but serious problems with the use of only Grignard reagents, which leads to reduction and aldol side products, and the yield of desired alkylation products could be improved.     

Alcoylation des enolates de l'acetylacetate d'ethyle dans le dimethoxyethane. Reactivite des formes associee et dissociee

The alkylation of alkali metal and N⁺Bu₄ ethylacetoacetate énolates by means of ethyl iodide, bromide and tosylate has been studied in diméthoxyéthane, in order to measure the reactivity of the associated forms. C/O alkylation ratios, structures of O-alkylated products and rates of alkylation, have been determined. With ethyl tosylate, the amount of O-alkylated products does not increase in the generally observed order Li⁺ < Na⁺ < K⁺ < Cs⁺ but in the order Na⁺ < K⁺ < Li⁺ ≈ Cs⁺. Some aspects of the alkali ethylacetoacetate énolates reactivity in weakly polar medium such as DME are discussed.     

Hydrogenation asymetrique de precurseurs d'aminoacides a l'aide de mono- et diphosphines derivees de sucres

Mono- and di-phosphines derived from sugars are synthesized and used as ligands in asymmetric catalysis. In the presence of a base (triethylamine, KOH…) the cationic complex [Rh(COD)dioxop]⁺ClO₄^?, catalyzes reduction of α-amino acid precursors with high optical yields (78–86%). The influence of the base is discussed.     

Polymerisation du methacrylate de methyle par le chlorure de tertio-butylemagnesium en solution dans le tetrahydrofuranne—I Etude de l'equilibre de dissociation du chlorure de tertio-butyle-magnesium

The thermodynamics of the dissociation of tBuMgCl have been carefully studied by PMR taking into account the exact concentrations of the various components. The Schlenk equilibrium should mainly be governed by the formation of different complexes for which degrees of solvation depend on the Grignard concentration. Owing to the estimated values of ΔH and ΔS, at low temperature in THF. MgCl₂ precipitates and only the symmetrical form tBu₂Mg initiates the polymerization of methylmethacrylate.     

Selectivite de la reduction d'α-enones polycycliques par les borohydrures: effet de l'addition de tetramethyl-ethylenediamine au borohydrure de tetrabutylammonium

3^1,9octalone, 3^1,9-10-methyl octalone and testosterone were reduced by NBu₄BH₄. alone or in the presence of tetramethylethylenediamine (TMEDA), in THF and in toluene. With TMEDA, the first step of the reduction is the regioselective 1,4 attack by BH^?₄ which leads either to the saturated ketones or to the corresponding saturated alcohols. The results observed under different conditions were interpreted by the intervention of various reductive species: diborane, enoxyborohydrides in the absence of TMEDA, amine-borane in its presence.     

Dosage de l'oxygene dans l'uranium et ses composes par la methode au monochlorure de soufre

A sulfur monochloride method is proposed for the determination of oxygen in uranium compounds. Sulfur monochloride reacts with oxygenated compounds at temperatures depending upon their nature; the sulfur dioxide produced is titrated by iodometry, after the excess reagent has been eliminated by a selective adsorption-desorption process using activated charcoal. This method has been successfully applied to uranium oxides (UO₂, U₃O₈), to mixtures of uranium dioxide with uranium, uranium nitride, and uranium carbide, and to substituted carbides (UC_1-xO_x). The results are generally satisfactory for oxygen contents higher than 500 p.p.m. However, in the presence of free or combined carbon, this limit is considerably higher. A loss of oxygen as carbon monoxide is also possible, and a simultaneous determination of carbon monoxide must be carried out. The relative error is of the order of a few per cent.     

Dosage de l'americium par coulometrie a potentiel impose

A coulometric determination of americium by reduction of Am(VI) to Am(V) at a potential of + 1.3 V is proposed. The accuracy of the method was evaluated by analyzing ²⁴¹Am solutions prepared by weighing and dissolving AmO₂ of known purity. The results must be corrected by a factor of 1.017, in order to eliminate the systematic error due to autoreduction. After this correction, the relative standard deviation of the method ranged from 0.44% for américium concentrations of 3.125·l0^-3M to 0.96% for those of 1.25·10^-4M.     

Nickel-phosphine complex-catalyzed Grignard coupling—II : Grignard coupling of heterocyclic compounds

A general, versatile method for alkylation and arylation of haloheterocyclic compounds is reported. In the presence of a catalytic quantity of [NiCl₂(dppp)], where dppp stands for Ph₂P(CH₂)₃PPh₂, bromothiophenes, halopyridines, haloquinoline, and haloisoquinolines reacted with alkyl and aryl Grignard reagents at room temperature or at ether refluxing temperature to give the cross-coupling products. The coupling reaction has been applied to the synthesis of isoquinoline alkaloids. Reactivities of 2-thienyl and 2-pyridyl Grignard reagents have also been examined.     

Selectivite de la reduction de l'androsten-4 dione-3,17 et de la progesterone par divers borohydrures: role de l'assistance electrophile par le cation ou un solvant hydroxyle

The reduction of Δ⁴-androsten-3, 17 dione 1 and of progesterone 2 by nBu₄NBH₄ is highly chemioselective: in THF only the a-enone moiety is reduced, the saturated C₁₇ or C₂₀ keto group being kept unchanged. When TMEDA is added, saturated alcohols are obtained, without any allylic alcohol when the reaction goes to completion. However this reduction is poorly stereoselective as 70:30 mixtures of A/B cis and trans ring junction compounds are obtained. In MeOH, the saturated keto group is more than 90% selectively reduced. However, the reduction of 1 and 2 by LiBH₄ and Zn(BH₄)₂ is poorly chemioselective. These results are interpreted in terms of competition between electrophilic assistance and steric effects.     

Reaction d'un thiolate de molybdene sur l'hexafluorobutyne

Bis(methyl)disulphide and the organometallic compound {(Cp)Mo(CO)₃}₂ in low oxidation state under photolysis give especially with the hexa-fluorobut-2 yne a 18-electron olefin complexe {(Cp)Mo(CO)₃(CF₃C₂CF₃SCH₃)}. The new compounds are reported and the reaction discussed.