Maurice Chastrette

REACTIONS DE CYCLOADDITION 4+2 SOUS MICRO-ONDES DES DERIVES DU GLYOXAL

Resume Hetero Diels-Alder reactions of methylglyoxylate and glyoxal monoacetal with 2-methyl-1,3-pentadiene have been studied under pressure in a microwave oven. Reaction times were dramatically reduced and degradation and polymerisation were avoided.

Structure–minty odour relationships: suggestion of an interaction pattern

Structure–odour relationships for the minty note were studied using a set of 150 compounds (68 minty and 82 not minty) with known olfactory descriptions and chemical structures. The study was based on the HBD (hydrogen bonding and dispersion) theory which considers that interactions involving molecules and receptor sites are mainly hydrogen bonds and dispersion forces. All the compounds of the set were examined and a combination of direct comparisons and chi-square tests allowed identification of relevant structural elements for the minty note. Twenty-four compounds (8 menthol isomers, 4 menthone isomers and 12 carveol and carvone derivatives) were chosen for their very precise olfactory description and because they constitute 12 enantiomeric pairs. Their low-energy conformations were computed using the Sybyl force field. Superimpositions on reference compounds of the likely conformations of each enantiomer were made using the Sybyl package, taking into account relevant structural elements previously identified. These comparisons showed that substituents in minty compounds must meet precise geometrical requirements and that, in spite of differences of location and nature for the functional oxygen group, they can receive a hydrogen bond from the same hypothetical atom of the receptor sites. Finally, from these structural and geometrical characteristics, an interaction pattern was proposed for the minty odour.

Une synthese simple et tres stereoselective de la d, 1-muscarine

Resume d,1-muscarine 1 , a molecule with three asymetric centers, was obtained from the methylvinyl ketone in six steps including two highly stereoselective reactions : the zinc borohydride reduction of an α, β-epoxyketone and the cyclization of an olefinic benzylether with iodine.

L’intensité de l’odeur des mélanges binaires de composés odorants

This paper presents the MBO model for the perceived intensity of odour mixtures. This model is based on an equation previously reported by our team, intended to model the whole stimulus-response intensity curve of pure odorous compounds. The MBO model was applied to a set of published data, and compared to other published models. The results show a high modelling efficiency of the MBO model compared to other proposed equations, especially for binary mixtures exhibiting significant asymmetry of intensity for different ratios of the two components. Furthermore, the MBO model includes parameters specific to the respective effects of each component in the mixture, which may help to clarify the masking and synergy effects that are often sought in odour mixtures.

Une nouvelle synthèse totale de la L(+) et de la D(−)-muscarine

Abstract L(+)-muscarine and its enantiomer have been prepared in 8 steps from D- and L-threonine respectively via the highly stereoselective iodocyclization of a γ,δ-unsaturated benzylether.

Ouverture regioselective d'alcools tetrahydrofuranniques par Me3SiCl/NaI synthese de L'exo-ET DE L'endo-brevicomine

Abstract Me 3 SiCl/NaI in acetone opens regioselectively tetrahydrofurfurylalcohols and hydroxy-3 tetrahydrofuran to give the corresponding iodoacetonides in good yields. An application to the synthesis of the exo-and endo-brevicomins is described.

A highly stereoselective route to substituted bis-tetrahydrofurans from 1,5-dienes.

Abstract Bis-tetrahydrofurans 1a and 1b , containing four chiral centers, are obtained with a 90 % isomeric purity from geranyl and neryl chlorides in four steps including two stereoselective cyclizations.

Reaction de complexes organocalciques sur les cetones

Abstract Ketones react with CaZnR4 and CaAl2 Et8 to give yields and addition/ reduction ratios greater than those obtained with mixed organocalcium compounds, RCaI. The -ate complex CaZnR4 is much more reactive than either ZnR2 or CaR2.

Synthese stereoselective du decadiene-2(E),4(Z)oate d'ethyle a partir d'un monoacetal du glyoxal

Abstract The glyoxal monoacetal 2 , now readily available in bulk quantity, is a very useful synthon for the dienes-1,3 synthesis, as illustrated in the stereoselective preparation of ethyl 2E, 4Z-decadienoate using two Wittig-type olefination reactions.

Réactions d'organocalciques sur des cétones aliphatiques

Abstract Reactions between organocalcium iodides and ketones in THF lead mainly to secondary alcohols. The insoluble part of the suspension of the organocalcium reagent causes only reduction, the soluble fraction (about 4 X 10 −2 M in organometallic reagent) reacts similarly to organomagnesium compounds. The addition reaction is favoured over the reduction when ketone is introduced during the synthesis of the organocalcium compound. The mechanisms of these reactions involve radicals at least partly.