Françoise Hénin

ASYMMETRIC PROTONATION OF ENOLIC SPECIES : DRAMATIC INCREASE IN THE SELECTIVITY WITH TEMPERATURE AND UNEXPECTED EYRING DIAGRAM

Abstract The palladium-induced cleavage of β-ketosters and enol carbonates derived from α-alkylated 1-indanones and 1-tetralones in the presence of (+)- endo -2-hydroxy- endo -3-aminobornane led to ( R )- α -alkylated indanones and tetralones with a large increase in the enantioselectiviy (up to 38–40%) when the reaction temperature was raised from 21 to 45–70°C. Thus, enantiopure 2-methyl-1-indanone was obtained at 52°C. More than one inversion temperature has appeared in plotting the corresponding Eyring diagrams.

Palladium(II)-mediated oxidation of alcohols using 1,2-dichloroethane as Pd(O) reoxidant

Abstract The oxidation of primary and secondary, saturated, allylic or benzylic, alcohols is carried out in 1,2-dichloroethane at reflux using catalytic amounts of both PdCl 2 and Adogen 464 in the presence of an excess of sodium carbonate. High selectivities are obtained from saturated and benzylic, secondary alcohols. Primary alcohols afford mixtures of aldehydes and esters. The migration of the double bond of α,β-unsaturated alcohols is a competing reaction. It is clearly shown that 1,2-dichloroethane reoxidizes the Pd(O) species.

Palladium nanoparticles obtained from palladium salts and tributylamine in molten tetrabutylammonium bromide: their use for hydrogenolysis-free hydrogenation of olefins

Carbon-carbon double bonds have been selectively hydrogenated at room temperature in the presence of benzyloxy groups using an atmospheric pressure of hydrogen, toluene or [bmim]PF6 as the solvent and palladium nanoparticles stabilized with tetrabutylammonium bromide. The system [bmim]PF6/palladium nanoparticles can be recycled without noticeable decrease of activity.

Telomerization of butadiene with pentoses in water: selective etherifications

Conditions have been developed to achieve the palladium catalysed telomerization of butadiene with L-arabinose and D-xylose in aqueous medium. The success of the reaction requires the presence of a tertiary amine as promoter with a catalytic system based on Pd–TPPTS. The etherification first occurs on the anomeric hydroxyl and, depending on the amine used, a second etherification leads to formation of the diether.

Palladium-catalyzed cleavage of prochiral enol carbonates: Enantioselective ketonisation of resulting enols☆

Abstract The palladium-catalyzed deprotection of (2-methyl-1-indenyl) benzyl carbonate and (2-methyl-1-indenyl) allyl carbonate in the presence of (+) or (−)ephedrine has led to 2-methyl-1-indanone with enantiomeric excesses of up to 40%.

Synergy or Competition between Palladium-Catalysis and KF/Alumina-Mediation for the Allylic Substitution of the Acetates of Baylis-Hillman Adducts by Phenols

Abstract The addition of various substituted phenols [XC6H4OH, X=H, o-CHO, o-CO2Me, o-CO2CH2Ph, o-CN, m-NHCOMe, m-OMe, p-OMe, p-CHO, p-Cl] to allylic acetates obtained from Baylis–Hillman adducts [RCH(OAc)C(CH2)CO2Et, R=H, n-Pr] has been studied in the presence of a Pd(0) catalyst and/or KF/alumina. In some cases, the use of one of these two reagents was sufficient to promote the OAc/OAr exchange but in general, faster reactions and higher yields were achieved when both reagents were used together. Evidence for two routes, an η3-allylpalladium intermediate and a Michael addition/elimination, was then obtained while a Heck type reaction could be involved under neutral conditions.

Diastereoselective synthesis of vinylmorpholines by palladium-catalyzed tandem allylic substitutions using enantiopure aminoalcohols as bifunctional nucleophiles

Abstract Enantiopure vinylmorpholines have been prepared by a diastereoselective disubstitution ( de up to 92%) of (Z) ROCH 2 CHCHCH 2 OR (R = Ac, CO 2 Me) by aminoalcohols in the presence of palladium catalysts.

Catalytic asymmetric protonation of fluoro-enolic species: access to optically active 2-fluoro-1-tetralone

Abstract Three racemic α-fluorinated benzyl β-ketoesters have been synthesized by electrophilic fluorination with Selectfluor™. They were submitted to our well established palladium-mediated cascade reaction (deprotection, decarboxylation and protonation of the resulting enolic species) producing optically active α-fluoro ketones. With benzyl 2-fluoro-1-tetralone-2-carboxylate as substrate, ( S )-(−)-2-fluoro-1-tetralone with up to 65% enantiomeric excess was obtained using quinine as the chiral base and Pd/C type 807104 from Merck as the heterogeneous catalyst.

Production of optically active ketones by a palladium-induced cascade reaction from racemic β-ketoesters.☆

Abstract 2-Methyl-1-indanone and 2-methyl-1-tetralone have been obtained with enantiomeric excesses of up to 52% from the corresponding benzyl and allyl β-ketoesters by a multistep reaction: palladium-catalyzed cleavage / decarboxylation / chiral aminoalcohol-mediated enantioselective protonation. The success of the process and particularly of the first step can be very dependent on the nature of the palladium catalyst used.

Palladium-catalyzed dehydrogenation of benzylic alcohols in molten ammonium salts, a recyclable system †

Heating secondary benzylic alcohols in molten tetra-n-butyl ammonium bromide with catalytic amounts of palladium chloride under a gentle flow of argon produced corresponding ketones in good yields. Neither cooxidant nor additive were required, with the added advantage of catalyst and ammonium salt recycling. The dehydrogenation of primary benzylic alcohols was less selective. Such a reaction was ineffective from allylic and saturated alcohols.