Robert Nouguier

Et3B- and Et2Zn-Mediated Radical Additions to Glyoxylate Imines, Compared Stereoinductions

Abstract 1,3-Stereoinduction in the addition of alkyl radicals to glyoxylic imines derived from various chiral amines has been investigated. New synthetic methodologies involving Et 3 B and Et 2 Zn as mediators have been compared. Dihydro-1,4-oxazin-2-one ( 2b ) gave the highest d.e. but no chemoselectivity. Open chain analogues derived from β-alkoxyamines led to good stereoinduction when the reaction was performed with Et 2 Zn which is a bidentate complexing reagent.

Transacetalisation de triols à partir du diméthoxyméthane. Sélectivité et applications synthétiques

Resume The LiBr assisted/acid catalyzed transacetalation of triols from DMM affords a highly selective method for the synthesis of hydroxy compounds bearing a dioxane ring. These compounds might further conveniently be alkylated by phase transfer catalyzis.

Stereoselective free-radical cyclization on a sugar template the sulphonyl radical as a synthetic tool for functionalized glycosides

Abstract The addition of a sulphonyl radical to the external double bond of an allyl glycal generates a pro-chiral carbon radical which adds to the glycal double bond with a high diastereoselectivity. Through three consecutive radical steps, the configurations of three new asymmetric centers are controlled.

Stereocontrol in radical cyclizations on sugar templates

Abstract The radical cyclization of alkyl hex-2-enopyranosides provides a stereocontrolled route to fused furanopyranes. The intermediate radical is generated either via the reduction of the appropriate halide by tin hydride or via sulfonyl radical addition to allyl hex-2-enopyranosides. The two methodologies are compared with respect to diastereoselectivity. Stereocontrol is discussed on the basis of conformational preference in the transition state.

Réactions SRN1 en série hétérocyclique. IV: Réactivité des sels du diméthyl-2,2 nitro-5 dioxanne-1,3

Abstract 2-Alkyl 2-nitro 1,3-propanediol, 2-alkylidene 1,3-propanediol and 2-dialkylidene 1,3-propanediol are prepared via S RN 1 reactions with salts of 2,2-dimethyl 5-nitro 1,3-dioxane and acid-catalyzed cleavage of the resulting acetals.

4-Isopropenyl-3-tosylmethyl pyrrolidines through radical cyclizations of 4-aza-1,6-dienes - an approach to kainic acids

Abstract The cyclofunctionalization of 4-aza-1,6-dienes 1 and 2 - bearing a prenyl chain - via the radical addition of PhSeTs ( 4 ) has been investigated as a potential route to 4-isopropenyl-3-tosylmethylpyrrolidines. Since the oxidative elimination of the resulting selenides afforded mainly the undesired olefinic regioisomer, an alternative pathway via the rearrangement of allylic sulfones 10–11 , was applied and provided, in good yields, the target heterocycles; 12 a, b are potential precursors of kainic acids.

Ligand assited asymmetric synthesis. II. Diastereoselective Diels-Alder additions with Lewis acid attracting auxillaries derived from pentitols

Abstract The dimethylene acetals of the three pentitols and methylene acetal of 1,2,4-butanetriol behave as effective templates for the diastereoselective Diels-Alder reaction. The chirality transfer occurs through a chelate-complex involving one of the dioxane rings.

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.

Reactivite du tris(hydroxymethyl)aminomethane avec des nitro-aldehydes aromatiques. Synthese de nouveaux composes antimicrobiens.

Abstract Heterogeneous reaction of TRIS 1 with nitro-aldehydes leads to oxazolidines in good yield. New products are obtained as monocyclic or bicyclic compounds, and are of potential medicinal value.

INTRAMOLECULAR RADICAL ALLYLATION WITH ALLYLIC SULFONES : A SYNTHESIS OF ()-BOTRYODIPLODIN

Isopropenyl-5-membered-ring acetal or lactone are potential precursors of (±)-botryodiplodin (1). Several pathways, involving 5-exo-trig ring closure onto allylic sulfones, have been investigated. The iodine atom transfer methodology allowed the preparation of the desired skeleton through intramolecular addition of an α-alkoxycarbonyl radical to the double bond of the appropriate allylic ethyl sulfone. Subsequent deprotonation and kinetic reprotonation led to the key precursor14 with a high stereoselectivity. Download full-size image