Paulette Viout

Transfert de phase solide- liquide : influence de l'agent de transfert sur la reaction de formation de cyclopropanes

Resume Cyclopropanic esters are obtained in a solid- liquid medium, in the presence of a phase- transfer reagent. The stereoselectivity results are interpreted by a reaction in the organic solvent.

Alkylation directe de cetones et d'aldehydes en presence de potasse solide en suspension

Abstract Dehydrated solid KOH, suspended in aprotic solvents, is used as a base for ketone and aldehyde alkylation. The best solvent as regards yields and selectivity is DME. The quantity of KOH depends on the carbonyl compound acidity. This method gives as good results as less convenient homogeneous conditions.

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

Abstract The reduction of Δ 4 -androsten-3, 17 dione 1 and of progesterone 2 by n Bu 4 NBH 4 is highly chemioselective: in THF only the a -enone moiety is reduced, the saturated C 17 or C 20 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 LiBH 4 and Zn(BH 4 ) 2 is poorly chemioselective. These results are interpreted in terms of competition between electrophilic assistance and steric effects.

Stereoselectivity of a polymer supported reaction

Abstract the substitution of Cl by PhCH 2 - CO 2 - and CH 2 = CH - CO 2 - in a soluble chloromethylated polystyrene leads to polymer supported esters which were used for the preparation of cyclopropyl derivatives. For the first time at our knowledge, a reaction was performed between two funntionalized polymers. The polymer backbone effect on the reaction with one or two bound reagents is not large, and it depends on the temperature.

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

Abstract ‡1,9octalone, ‡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.