David Abenhaim

Synthesis of Jasminaldehyde by Solid-Liquid Phase Transfer Catalysis Without Solvent, Under Microwave Irradiation

Abstract α-n-amylcinnamaldehyde (jasminaldehyde) was obtained with 82 % yield by solid-liquid phase transfer catalysis without solvent within 3 days at room temperature. By use of domestic microwave irradiation, the same yield was obtained within 1 minute at a power of 600 W.

A SHORT AND EFFICIENT SYNTHESIS OF KETENE O,O- AND S,S-ACETALS UNDER FOCUSED MICROWAVE IRRADIATION AND SOLVENT-FREE CONDITIONS

Abstract A new methodology leading to ketene O,O- and S,S-acetals is reported. The title compounds were prepared from the corresponding halogenated precursors under microwave irradiation in the absence of solvent within 5–25 minutes with excellent yields. Yields obtained under microwaves are by far the best when compared to those obtained by ultrasound or classical heating in the same conditions of time and temperature.

Réduction des époxydes par les trialcoylaluminiums

Abstract The reaction is studied between epoxides and trialkylaluminium compounds containing a hydrogen atom in position β with respect to the metal atom. These organometallic compounds which are generally known to be capable of adding on to epoxides are shown to be equally suitable for reducing them. The ratio addition/reduction is largely dependent on the epoxide considered. To our knowledge, magnesium compounds have not been observed to undergo a similar reaction. A detailed study of the reaction of triisobutylaluminium with styrene oxide has been carried out. This establishes essentially that the ratio addition/reduction is independent of the time of contact of the reactants, the ratio of reactants, the temperature and the substituent carried by the aromatic part of the epoxide. A mechanism is suggested to account for the observed phenomena. This involves two molecules of the aluminium compound and an epoxide molecule, reacting via the formation of a cationic carbon compound and i-Bu − 4 Al.

The ate complexes of aluminium: Reactivity and stereoselectivity with respect to epoxides and carbonyl compounds. Catalytic activation by salts of transition metals

Abstract When used in non-coordinating solvents (hydrocarbons) NaAlEt4 and LiAlnBu4 are good alkylation agents for epoxides. The presence of catalytic quantities of transition-metal salts, particularly NiCI2 or NiBr2, greatly accelerate the reactions, making them possible within a reasonable time in the case of disubstituted epoxides such as cyclohexene oxide, 2-3 epoxybutane, 1 phenyl-2,3-epoxybutane. In the case of aliphatic epoxides, dialkylmagnesium, NaAlEt4 and LiAlnBu4lead mainly to alkylation of the least substituted carbon of the epoxide ring; while in the case of epoxides with a C-O bond in the benzyl position, it is this carbon that is alkylated. The reaction always proceeds by total inversion of the configuration of the carbon in the epoxide ring, namely the site of the alkylation. NaAlEt4 is also a good agent for alkylating carbonyl compounds when used in solvents of low basicity such as diethylether, or in totally non-coordinating solvents such as the hydrocarbons. The yields of the alcohol are greatly improved by using catalytic quantities of NiCl2. The behaviour of NaAlEt4 with 2-phenylpropanol is quite remarkable: in diethylether NaAl-Et4 gives predominantly the pair of enantiomers predicted by Crams rule, and with greater stereoselectivity than if EtMgBr was used, while in pentane the reaction is no longer stereoselective. Finally, with a cyclic ketone, 4-t-butylcyclohexanone, NaAlEt4 in diethylether and in hexane in the presence of NiCI2 gives predominantly the equatorial alcohol resulting from an axial attack, which is generally not favoured at all.

Asymmetric alkylation of carbonyl compounds with lithium or sodium tetraalkylaluminates modified by chiral aminoalcohols

Asymmetric alkylation of benzaldehyde and acetophenone by modified aluminium “ate” complexes are reported. LiAlMe4, NaAlEt4, LiAln-Bu4, NaAln-Bu4 modified by either (−)-N-methylphedrin or (+)cinchonine or (−)quinine were used. Using hydrocarbon solvents and sometimes under nickel catalysis the treatment of carbonyl compounds by modified “ate· complexes produced chiral alcohols with both chemical and optical good yields. NaAlEt4 modified by (−)-N-methylephedrin reacted with benzaldehyde to give S(−)1-phenyl-1 propanol in 20% enantiomeric excess. The same reagent reacted with acetophenone to give S(−)2-phenyl-2 butanol in 33% e.e. NaAln-Bu4 modified by (−)-N-methylephedrin reacted with benzaldehyde to give S(−)1-phenyl-1-pentanol in 27% e.e. or with acetophenone to give (−)2-phenyl-2-hexanol in 44% e.e. Since a wide range of new asymmetric alkylating reagents has been obtained from aluminium “ate” complexes and chiral compounds, it can be assumed that the method described could be useful to synthetise chiral alcohols with high optical yield.

Stereochiimie de la reaction du dicrotylmagnesium et du dicrotylzinc vis-a-vis de cyclohexanones monoalcoylees

Abstract Pure dicrotyl-magnesium and -zinc react with 2-methyl-, 3-methyl-, 4-methyl- anf 4-t-butyl-cyclohexanone quantitatively by predominantly equatorial attack by the organometallic reagent. Dicrotylzinc is more stereoselective than dicrotylmagnesium.

Comportement d'un organomagnesien symetrique non solvate (s-Bu2Mg) vis-a-vis d'un epoxyde terminal, le phenyl-1 epoxy-2,3 propane

Abstract Di-s-butylmagnesium reacts in pentane with 1-phenyl-2,3-epoxypropane, giving besides the expected alcohol (1-phenyl-4-methylhean-2-ol), an alcohol resulting from direct reduction of the epoxide group. Such a reaction has previously been observed with organoaluminium compounds, but not with organomagnesium compounds. When the ratio s-Bu2Mg/epoxide = 2 the reaction is very fast in alkanes but slow in diethyl either. In this last solvent, besides other products, cinnamic alcohol is formed.