Jean-Pierre Roque

BiBr3, an efficient catalyst for the benzylation of alcohols: 2-phenyl-2-propyl, a new benzyl-type protecting group

Abstract The benzylation of aliphatic alcohols with various benzylic alcohols has been achieved in the presence of BiBr3 under mild conditions. 2-Phenylpropan-2-ol proved to be the most efficient and can be considered as a novel protecting group.

Reactivity of bismuth(III) halides towards alcohols. A tentative to mechanistic investigation

Abstract The reactivity of bismuth(III) halides (BiX 3 ; X=Cl, Br and I) towards a series of alcohols has been investigated. Three different reactions have been studied, namely: halogenation, dehydration and etherification. The behaviour of these bismuth derivatives was found to depend on the nature of the halide bonded to the bismuth atom. Their reactivities can be interpreted on the basis of the Hard and Soft Acids and Bases (HSAB) principle. A mechanism is proposed which involves the formation of a complex of the alcohol with Bi(III).

Reactions d'addition nucléophile sur les cétones : Addition de l'ion sulfite: mise en évidence de l'hyperconjugaison Par la mésure de l'éffet isotopique sécondaire du deutérium

Resume The rates of addition, at 25° in water, of the SO3−− ion to nine saturated ketones and their ga-deuterated homologs have been measured. The secondary kinetic isotope effects, expressed by the ratios (kH/kD)f, have been determined. We have also measured the isotope effect during the hydrolysis of bisulfite addition compounds of twelve ketones: (kH/kD. These isotope effects are discussed in terms of electronic and steric factors. The transition state has been shown to be ”reactant-like” for the addition reaction: the inductive and steric factors are of little importance, if any. The main factor, responsible for the isotope effects, seems to have a hyperconjugative origin: the deuterated ketone is less stabilized by σ-π8 overlap than the normal one. The variations of the isotope effect from one compound to another are easily interpreted by the consideration of the stable conformations of the ketone and the change of hyperconjugative stabilisation from one ketone to another.

BiBr3-Catalyzed benzylation of alcohols. Stereochemistry and mechanistic investigations

Abstract We have investigated the benzylation of optically active aliphatic alcohols (octan-2-ol and butan-2-ol) as well as cis and trans 2-methylcyclohexanol or ( S )-(−)-menthol, catalyzed by bismuth (III) bromide in the presence of (−) or (±)-1-phenylethanol (PeOH). Under mild conditions, aliphatic alcohols provided an equimolar mixture of diastereomeric ethers while alicyclic alcohols gave rise to ethers with retention of configuration. To explain these results, we assumed that BiBr 3 , acting as Lewis acid, would lead to the formation of a 6-fold coordinated bismuth intermediate involving two molecules of 1-phenylethanol and one molecule of aliphatic alcohol. We have proposed a mechanism to explain these BiBr 3 -promoted etherification reactions.

BiX3 as an efficient and selective reagent for the halogen exchange reaction

Abstract Bismuth halides are efficient and selective reagents in the halogen exchange reactions carried out under mild conditions. This rapid, high yield reaction proceeds mainly with retention of configuration.

BiCl3: An Efficient Agent for Selective Chlorination of Alcohols or for Halogen Exchange Reaction

Abstract BiCl3 was found to be an effective reagent for an improved chlorination of alcohols and for a convenient halogen exchange reaction.

Anomeric effects in non-carbohydrate compounds: conformational differences between the oxazolidine rings of a cis-fused bicyclic system

Tris(hydroxymethyl)aminomethane (Tris) can react with benzaldehyde (1:2 molar ratio) to produce cis-2,8-diphenyl-5-hydroxymethyl-1-aza-3,7-dioxabicyclo[3.3.0]octa ne, the structure of which has been confirmed by nuclear magnetic resonance spectroscopy and X-ray crystallography. The crystal structure showed that both oxazolidine rings A and B are puckered in opposite directions. Ring A exists in an E3 envelope form with 0-3 noticeably down (0.65 A) the plane of the remaining atoms, whereas ring B adopts the 7E envelope conformation with the 0-7 atom displaced up from the mean reference plane by 0.70 A. Comparison of bond angles and bond distances showed that both oxazolidine rings A and B exhibit cross endo-anomeric effects resulting from electron delocalization over the bond sequence O-3-C-2-N-1-C-8-O-7.

Inverse Phase Transfer Catalysis. III.-Optimization of the epoxidation reaction of α,β-unsaturated ketones by hydrogen peroxide

Abstract The epoxidation of chalcone using hydrogen peroxide in the presence of a base in a two-phase medium system following the so-called Inverse Phase Transfer Catalysis (IPTC) process was investigated. Careful examination of various parameters including surfactant concentration, pH, H2O2 decomposition side-reactions and epoxide ring-opening, allowed us to determine optimal experimental conditions

Bi(III) carboxylates as efficient reagents for preparation of esters under mild conditions. A new method for the protection of carboxylic acids

Abstract Bi(III) carboxylates have been obtained by reaction of triphenylbismuth with various monocarboxylic acids. By a ligand-exchange reaction, these Bi(III) carboxylates react with tertiary or benzylic-type bromides and afford esters. This reaction sequence constitutes a new efficient way for the temporary protection of carboxylic acids under mild conditions.

Efficient catalytic activity of polymerized micelle-forming surfactants

Abstract Micellar catalysis in the hydrolysis of para-substituted benzaldehyde diethylacetals by sodium 10-undecenyl sulfate is enhanced by polymerization of the surfactant aggregates.