Jean-Louis Gras

Methoxymethylation of tartrate as a strategy for the synthesis of chiral building blocks

Abstract Controlled methoxymethylation of tartrate affords mono- and diMOMtartrates. We took advantage of the particular reactivity of methoxymethylethers and of the conformations of the starting C4 unit, to efficiently synthezise various cyclic methyleneketals (dioxane and dioxolane) or cyclic ethers (oxolane and oxetane).

Re´activite´dume´so-erythritol et du thre´itol visa`vis de la reaction de transace´talisation par le dime´thoxyme´thane

Abstract The TsOH catalized-LiBr assisted transacetalization from dimethoxymethane applied tomeso-erythritol1 and threitol5 allows the selective synthesis either of (4,4,0)-oxabicyclic compounds2 and6 or of 1,3-diols3 and7. The relative configuration of the central carbon atoms proved to be critical to the reactivity of each tetraol, and is a key-factor for the determination both of the number and the structure of the expected products from this transacetalization to a given polyol. A reinvestigation on the reaction ofmeso-erythritol or threitol and formol provides a more accurate scope of this method of methylenation.

Methyl 3,4-O-methylene-β-D-arabinoside as a new chiral template for the asymmetric diels-alder reaction

Abstract The acrylate of the methyl 3,4-O-methylene-β-D-arabinoside is a very stable and efficient chiral dienophile for asymmetric Diels-Alder reactions with cyclopentadiene, isoprene and dimethyl butadiene.

A convergent strategy toward linear cis-skipped polyenes

Abstract An easy preparation of symmetric Cis-skipped polyenic hydrocarbons 1 to 5 combining the controlled classical Wittig reaction or the oxidative dimerization of phosphoranes is described.

Chiral conformationally restricted arachidonic acid analogs based on a 1,3-dioxane core

Abstract Chiral building blocks derived from l -diethyl tartrate are derivatized into various chiral arachidonic acid analogs based on a dioxane core.

Chemical shifts of ethylenic carbons in polyunsaturated fatty acids and related compounds

The 13C NMR of ethylenic carbon atoms in the methylene‐interrupted cis double bonds as found in polyunsaturated fatty acids (PUFAs), their precursors and analogs was studied. The chemical shifts of unsaturated carbon atoms are strongly dependent on a combination of electric field effects from the head group, steric hindrance and the presence of other double bonds. A full set of shift parameters were determined based on a reference value given by a long aliphatic alkene (cis‐6‐dodecene at 129.99 ppm) and various functionalities (double bond, ester, aldehyde, acetal, hydroxyl methyl, etc.) with one, two and three double bonds. Application of shift parameters to polyfunctionalized polyenes, high PUFAs and new analogs of arachidonic acids shows that the method is a convenient way to predict the chemical shift of all ethylenic carbon atoms.

Réaction de Transacétalisation par le Diméthoxyrnéthane synthése de O-méthylèneacétal de dérivés du D(+)Glucose

Abstract The acid catalyzed and LiBr assisted tramacetalization from dimethoxymethane applied to α and β glucosides allows the selective methylenation of the −4 and −6 hydroxyl functions. The α anomer leads to the compound 4, but under the same conditions, the β anomer leads to a mixture of the methylene acetal protected carbohydrates 4 and 5. Glucose, under our transacetalization conditions, affords, after in-situ O-glycosidation and protection, the same compounds 4 and 5. The classical methylenation using formol/HCl with glucose and glucosides, does not lead to the expected products but to the same glucofuranoside compound 6 which results from a O-demethylation of the glucoside.

Selective Synthesis of β‐Hydroxy Nitroethanol Ethers by Alcoholysis of Oxiranes

Abstract β‐Hydroxy nitroethanol ethers are prepared by selective alcoholysis of oxiranes. The best results are obtained using a clay (monmorillonite K10) or a π‐acid (TCNE) as the catalyst.

Efficient Syntheses of Pure Mixed Triglycerides

Abstract Pure mixed triglycerides can be prepared from diglycerides and by acylolysis of glycerolformal tosylate without isomerization. The last fatty chain, with or without a functional group, can be introduced on any position of glycerol.

Synthesis of Methyl-O-4,6-methylene-D-mannopyranoside by Transacetalisation Reaction from Dimethoxymethane

Abstract Lithium bromide assisted transacetalisation of methyl-α-D-mannopyranoside (3) with dimethoxymethane led to the title compound (4) in moderate yield. Compound 4 is a new and stable monoacetal which is formed to the exclusion of the expected corresponding diacetal (5) or the rearranged diacetal (6).