H. Christol

Hydrolyse Basique de phosphonates I. Étude qualitative

Abstract The kinetics of the hydrolysis of methyl-, cyclohexyl-, and phenylphosphonates by sodium hydroxide in 50% water/dioxane have been studied. For a given ester group, the rate of this nucleophilic substitution increases slightly on going from the methyl- to the phenylphosphonates. In contrast, the reactivity of the cyclohexylphosphonates is much lower. For each of these types of phosphonate, the rate is strongly influenced by the nature of the organic radical in the ester group, and is very sensitive to steric effects. The mechanism of the reaction is discussed.

Inversion de polarite a4 des cetones α-alleniques par le groupe triphenylphosphonio

The a4 umpolung of α-allenic ketone sis performed using the triphenylphosphonio group. It results in inducing an electrophilic character at the carbon ψ to the carbonyl function and in changing the regioselectivity of the additions of active hydrogen compounds on the carbon-carbon double bond to give finally the adducts 4 (Fig. 1). This new umpolung method is illustrated here in the case of the addition of methanol on allenyl methyl ketone 1a (Fig. 2).

Arylation catalytique d'organophosphorés. Produits de l'arylation, catalysée par les sels de nickel (II), de composés du phosphore tricoordiné.

Abstract Analysis of the products from the nickel (II) bromide catalysed arylation of tricoordinated phosphorus compounds R 2 P-Z (Z  H, Cl, SR, NR 2 pointed out that this arylation always takes place on phosphorus resulting at first in formation of pseudophosphonium salts. Only the aminophosphonium salts are stable under reaction conditions; the other salts undergo several transformations which can be brought together in a general reactivity scheme to account for all the side products. On regard to other heteroatoms these results point out a particular ability of phosphorus to be arylated under nickel (II) catalysis. The reaction with secondary phosphines can be applied to synthetise diarylphosphonium salts.

Removal of Thioacetal Protecting Groups by Cerium (IV) Ammonium Nitrate - Hydrolysis of 1,3-Dithiannes

Abstract In the course of our work on umpolung of α,β-ethylenic ketones and aldehydes1, the use of thioacetalised γ-ketophosphonium salts and ylids led us to investigate the hydrolysis of 1,3-dithianes. Among the known methods of removal of thioacetal protecting groups2, the one using cerium (IV) ammonium nitrate (CAN) has the advantages of a fast reaction with easy work-up and good to very good yields3. This method has been widely applied for preparative purposes using four equivalents of the cerium salt. However it does not seem that a theoretical explanation has been brought for the use of such a quantity of CAN. The only one proposed4 deals with a mechanism similar to the one involving mercury (II) salts, where indeed, four equivalents of metallic salt are not necessary5.

LES TRIBROMURES DE PHOSPHONIUMS. AGENTS DE BROMATION DE SUBSTRATS ORGANIQUES

Abstract The reactivities and selectivities of phosphonium tribromides 1–4 towards ketones and their ketals, in the presence of other functional group reactive towards bromide (free enolic position, activated aromatic ring or double bond), are studied and compared with the trimethyl phenyl ammonium tribromide 5. The abilities of the two kinds of tribromides are similar, with a better selectivity of phosphoniums salts toward unsaturated ketones, which is probably induced by the greater stability of the ion-pair in phosphonium salts. They act essentially by the tribromide without specific bond interactions between phosphorus and heteroatom of the substrate.

SYNTHESE ET REDUCTION CHIMIQUE DE SELS DE VINYLENE-1,2 ET BUTADIENYLENE-1,4 BISPHOSPHONIUMS

Abstract Les sels de vinylene-1,2- et butadienylene-1,4-bisphosphoniums, o[ugrave] le phosphore est porteur des groupes labiles benzyle, cyano-2 ethyle, allyle ou phenyle, ont ete synthetises par reaction des phosphines tertiaires correspondantes avec le bromure d′acetyle ou de vinylacetyle. Lorsque ces sels sont traites par l′aluminohydrure de lithium, par des alcoolates ou des cyanures alcalins, l′encha[icaron]nement insature entre les deux atomes de phosphore est rompu selectivement, pour fournir une ou plusieurs phosphines tertiaires. Un mecanisme reactionnel a ete propose et discute pour chaque type de rupture: avec les ions alcoolate et cyanure, en particulier, la reaction correspond a la formation intermediaire d′ethynylphosphonium qui evolue vers les produits finaux. 1,2-vinylene- and 1,4-butadienylene-bisphosphonium salts with labile groups on phosphorus (e.g. benzyl, 2-cyanoethyl, allyl or benzyl) are synthetized in the reaction of the corresponding tertiary phosphines with acetyl- or vinylacety...

Ylures de γ-cétophosphoniums thioacétalisés comme équivalents synthétiques des anions β-acyléthyles et β-acylvinyles

Abstract α,β-Ethylenic ketones can be alkylated or acylated β to the carbonyl group, after inversion of polarity of these substrates using γ-thioacetalised phosphonium ylides as intermediates. The Wittig reaction carried out with thes ylides provides a way to thioacetalised β,???-ethylenic ketones.

Electrochemical reduction of 1,2-vinylene and 1,4-butadienylene bis-phosphonium salts

Abstract The electrochemical reduction of 1,2-vinylene and 1,4-butadienylene bis-phosphonium salts has been investigated on a mercury cathode in unbuffured or acidic hydroorganic media. It is controlled by ylid character of the radical obtained after the first electronic transfer. This ylid character induces an heterolytic PC bond breaking with the unsaturated bridge. This result parallels those obtained in the chemical reduction of the same structures and confirms the high fragility of the bridge.

Reaction des lithiens avec les organophosphores. Reaction d'addition du t-butyllithium sur le noyau benzenique des sels de phenylphosphoniums

Abstract A new reaction of organolithium compounds with phosphonium salts is described; reaction of t-butyllithium with dibenzylaminophosphonium or tetraphenylphosphonium bromides takes place through addition of the t-butyl group on a benzene ring at the position para to the phosphorus atom, the ylid formed reacts in a characteristic Wittig reaction with p -tolylaldehyde.

Contribution a la synthese de prostaglandines

Abstract A new general method for grafting the β chain of natural Prostaglandins and homologs is proposed.