Alain Rahm

Reduction of ketones by tributyltin hydride: the effect of high pressure on steric hindrance and rearrangement processes

Les cetones steriquement empechees sont reduites avec de bons rendements et les cetones cyclopropyliques ou epoxydiques conduisent aux alcools avec des tres hauts rendements et une preservation totale ou predominante du cycle a 3 membres

Hydrures organostanniques et syntheses asymetriques: obtention de quelques composes chiraux dans la serie des triorganostannyl-2 butanes et determination de leurs pouvoirs rotatoires maximaux

Abstract Chiral organic and organotin compounds have been synthesized by asymmetric reduction or hydrostannation of a α-β-unsaturated chiral esters. The enantiomeric purities of some organotin hydrocarbons have been established by NMR. A method of correlation is described, which allows the maximum optical rotation of other 2-trialkylstannylbutanes to be obtained.

High-pressure (4+2)cycloaddition of 1-methoxy-3-trialkylsilyloxybuta-1,3-dienes to butyl glyoxylate. Isolation of primary cycloadducts

Abstract High-pressure reactions of 1-methoxy-3-trialkylsilyloxybuta-1,3-dienes ( 1 , 2 ) with butyl glyoxylate ( 3 ) and isolation of the primary cycloadduct 5 as well as its simple chemical transformations are described.

Synthese et etude par resonance magnetique nucleaire du carbone 13 et de l'etain 119 d'une serie de triorganostannyl-2 butanes

Abstract Optically active triorgano-2-stannylbutanes have been synthetized by different methods, one being the direct substitution of optically active s-butyl halides with triorganostannyl alkali metals. This route involves a complete or partial inversion of configuration at the chiral carbon atom. Carbon-13 and tin-119 NMR data are reported as support for the identification of eight triorgano-2-stannylbutanes. The special case of tetra(2-butyl)tin, with four identical chiral centres has been examined.

The use of 119 Sn NMR for the investigation of organotin reactions

. 119 Abstract — Direct Sn NMR has been employed as a very useful tool for the investigation of a variety of organotin reactions. The high sensitivity of tin chemical shifts to small structural changes has been used for discrimi— nation between closely related isomers. Thus asymmetric hydrostannation of unsaturated chiral esters has been studied by means of the direct analysis of diastereoisomeric adducts in reaction mixtures. The three different configurational isomers of tetra—sec—butyltin have been distinguished and the results used for stereochemical study of electrophilic cleavage of the tin—carbon bond. Also other asymmetric induction processes have been evalua— ted. Alternatively nJ(SflD) coupling constants, which are very easily observed after suitable deuterium labelling, have given access to very fruitful information. The Karplus—like angular dependence of 3J(SnD) has been employed to determine the stereochemistry of several organotin Diels—Alder cycloadditions as well as the stereochemistry of alkene hydrostannations. For instance major cZn-t-L—addition was found in the hydrostannation of phenyl— cyclohexene while 4qn—addition was dominant in the case of norbornene derivatives. The stereochemistry and the regioisomerism of alkyne hydrostanna— tion has also been examined. Finally a complex analytical problem involving the regioselectivity and stereochemistry of the stannylation of allyl tosylates has been solved by the joint consideration of tin chemical shifts and coupling constants.

Stereochemistry of the tin—carbon bond: I. Synthesis and characterization by 13C and 119Sn NMR of a series of exo- and endo-2-triorganostannylnorbornanes

Abstract A series of endo - and exo -2-triorganostannylnorbornanes have been synthesized by various methods, some of them leading to pure stereoisomers. The 2-triorganostannylnorbornanes have been characterized by their 13 C and 119 Sn NMR spectra.

The absolute configuration of (+)-2-triphenylstannylbutane

Abstract The X-ray structural analysis of (+)-2-triphenylstannylbutane was undertaken in order to establish the absolute configuration of the molecule, using the anomalous scatter of Cu-K α radiation by tin atoms. The configuration of (+)-2-triphenylstannylbutane is S .

Chimie organometallique sous haute pression: Reaction des chlorocetones avec l'hydrure de tributyletain

Abstract High-pressure reactions of tributyltin hydride with several chloroketones (3- chloro-2-butanone, 4-chloro-2-butanone, 5-chloro-2-pentanone, 6-chloro-2-hexanone and 7-chloro-2-heptanone) led to the formation of chloroalkoxytins or cyclic ethers. An ionic mechanism, starting with nucleophilic attack at the carbonyl group, is proposed to explain the formation of the reaction products.

High Pressure Organometallic Chemistry : Diastereoselectivity in Diels Alder Reactions of 2,3-Dimethyl-1,3-Butadiene with (Z)-3-Tributyl-Stannylacrylic Acid (-) Menthyl Ester

Abstract The effect of pressure (0.1 to 25OO MPa) on the asymmetric induction in the cycloaddition between (-)-menthyl 3-tributylstannyl-acrylate and 2,3-dimethyl-1,3-butadiene has been investigated under different solvent and temperature conditions. The high pressure considerably facilitates the addition but leads to a decrease or even an inversion of the diastereomeric excess. This behavior can be explained by a favored cisoid conformation of the ethylenic ester under high pressure.

Asymmetric hydrostannation of chiral α,β unsaturated esters, a new exception to prelog's generalization

Abstract The stereochemical course of the radical hydrostannation of E and Z (−)-menthyl crotonate, under experimental conditions close to the kinetic control, is best taken into account by considering cisoid conformations for the substrates.