Bernard Barbe

C-silylation et duplication réductrice observées lors de l'action de Me3SiClMgHMPT sur des composés carbonylés α-éthyléniques. : Application à la préparation d'εdicétones à partir de cétones α-éthyléniques

Abstract Two reactions, the 1,4-disilylation and the reductive duplication accompanied by O -silylation, can chiefly occur by action of the Me 3 SiClMgHMPT system on various α-ethylenic carbonylated compounds. When the sequence of such derivatives is conjugated with another group , the 1,4-disilylation is the main reaction and affords upon hydrolysis the corresponding derivative β-silylated with respect to the carbonyl group (new illustrative example: the pseudo-ionone). In contrast to this, when the sequence is not conjugated with another group, the reductive duplication accompanied by O -silylation occurs and leads, after hydrolysis, to the corresponding e-diketone (examples: methylbutenone, 2-cyclohexenone and isophorone). Such a reaction can be used in organic synthesis to prepare e-diketones from α-ethylenic ketones. A mechanism permitting homogeneous interpretation of all our results in this domain is proposed.

Interet de la deuteriation des molecules organostanniques en RMN de 119Sn : II. Relation de type karplus pour 3J(SnD) et stereochimie de deuteriostannation de quelques hydrocarbures ethyleniques

Abstract Whenever selective deuterium labelling is easily performed a new proficiency is given to FT 119 Sn NMR by the determination of the angular dependence of 3 J (SnD). Using model molecules with structures being checked by other methods, the angular dependence of 3 J (SnD) has been shown to follow a Karplus-like relationship. Illustrative examples for the qualitative and quantitative analysis of diastereoisomeric organotin compounds are described. This method allows for instance, a fast and convenient determination of the stereochemistry of alkene deutero- and hydro-stannations.

A complete structural and conformational investigation of procyanidin A2 dimer

Abstract Structural and conformational study of A2 procyanidin is presented. By using NMR and molecular mechanics. A demonstration of the C4–C8 bond and of an additional C2-O-C7 ether linkage, characteristics of the procyanidin of A-series, was achieved.

Interet de la deuteriation des molecules organostanniques en rmn de 119Sn : I. Acces aux constantes de couplage nJ(SnD) et application a l'etude structurale de vinyl et d'allyletains☆

Abstract The selective deuteration of organotin compounds gives FT 119 Sn NMR a new proficiency, since it allows direct access to n J (SnD) coupling constants. Usually n J (SnD) is easily apparent for n  1, 2, 3 and sometimes 4 (allyltin compounds). This criterion has been successfully applied for qualitative and subsequently quantitative analysis of vinyltin and allyltin compounds. In the first series, the stereochemistry of alkyne deuterostannation has been easily explored, the assignments of configurations being made directly from 3 J (SnD) on the basis of 3 J (SnD) trans > 3 J (SnD) cis . In the second series, the method appears to be the best tool for simultaneous study of regiochemistry and stereochemistry in the substitution of 3-deutero-5-methyl-2-cyclohexenyl toluene sulphonates by trialkylstannyl anions. The choice between regioisomers was made on the basis of 2 J (SnD) >- 4 J (SnD). A further aspect of this work is the observation of isotopic effects on 119 Sn chemical shifts which were tentatively rationalized considering inductive, steric or hyperconjugative contribution of deuterium.

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.

Détermination de structures au moyen de la RMNn du 29Si: Transfert sélectif de population avec les méthylchlorodisilylméthanes

Abstract The selective population transfer (SPT) technique has been applied to 29 Si NMR of the complete series of methylchlorodisilylmethanes, several of which are new compounds. A great enhancement of the signals was observed and unambiguous assignments based on the determination of 2 J (SiH) coupling constants could be made. The first example of this type is presented.

A new preparation of hexaalkylditins. 119Sn NMR and chromatographic data on linear polytins

Abstract The reaction of triorganotin oxides and formic acid provides a good route to ditin derivatives. Several new linear polytin compounds have been isolated, and the vicinal and long range 119 Sn 119 Sn coupling constants determined. A linear relationship has been demonstrated between the logarithm of the HPLC retention time and the number of tin atoms in the compounds.

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.

Triméthylsilylcycloalcanes: Corrélation structure-réactivité

Abstract A comparative study of the physicochemical data (IR, Raman, 1H, 13C and 29Si NMR) of four trimethylsilylcycloalkanes, ( CH 2 ) n C HSiMe3 ( n = 2- 5), allowed a good correlation between their structure and chemical reactivity to be established. The particular chemical behaviour of trimethylsilylcyclopropane, in this series, involves an interaction between the three-membered ring and silicon, in good agreement with a (p → d)π interaction. This study provides a lot of new data for these models and exhibits exemplarily the contribution of physico-chemistry in explaining and predicting the chemical reactivity of organic substrates.

Biomimetic route to the strobane skeleton from methyl pimarate

Abstract From methyl pimarate a pimarane-strobane rearrangement in diterpene series is reported. This interconversion provides a biomimetic access to strobane derivatives.