Georges Manuel

Synthèses et réactivités comparées de sila- et germacyclopentanes fonctionnellement β-substitués

Abstract The synthesis and the chemical reactivity of 1-sila- and 1-germa-3-cyclopentenes (I), 6-oxa-3-sila and -3-germabicyclo[3.1.0]hexanes (II) and 1-sila- and 1-germa-3-cyclopentanols (III) are closely dependent upon the heteroatom M and its Σ substituents. Thus, bromine adds to ethylenic cycles (I) (3,4-dibromo-1-sila- and -1-germacyclopentanes stable for MSi, ΣMe, Ph and MGe, ΣBr, Ph are so obtained) and gives simultaneously ring opening reactions for MGe, ΣPh, Me. In the same way, concentrated halogen hydrides react on epoxides (II) and lead to cyclic halohydrins, stable for MSi, ΣPh and to linear products of β-decomposition for MSi, Ge; ΣMe. 1-Oxa-2,2-diphenyl-2-sila- and -2-germacyclopentanes (IV) are synthesised by oxidation of alcohols (III). Interpretation of experimental results accounts for different chemical behaviour of isologous Σ-alkyl-, aryl- and halosilicon and -germanium compounds.

Theory and application of photoelectron spectroscopy : XVI. Photoelectron spectroscopy and molecular conformations: GeC and SnC hyperconjugation and the conformation of allygermanes and -stannanes☆

Abstract The photoelectron spectra of vinyl- and allylgermanes and -stannes have been investigated. The conformations of allylgermanes and allylstannanes are shown to be determined by GeC and SnC hyperconjugation. The hyperconjugative ability of the CM(M = Si, C, Ge and Sn) bonding MOs with the ethylene π-MO is explained by simple perturbation theory. This result represents a new and independent confirmation of the hyperconjugative interaction mechanism.

α- et β-silacyclopentanols

Abstract 1,1-Dimethyl-1-silacyclopentan-3-ols are synthetised by hydroboration—oxidation or epoxidation—reduction of the corresponding silacyclopent-3-enes. In acidic media, β-silacyclopentanols give ring opening reactions. Secondary sila-β-alcohols are rearranged by Raney nickel on warming to give 1-oxa-2-sila-cyclopentanes. Thermal dehydration of tertiary β-alcohols gives a mixture of cyclenic isomers from which α-silacyclopentanols can be prepared. Silacyclopentane-3,4-diols are obtainable from the acidic cleavage of the epoxidic ring of oxasilabicyclohexanes.

The versatile behavior of the PdCl2/Et3SiH system. Conversion of alcohols to the corresponding halides and alkanes

Abstract The versatility of the palladium(II) chloride/triethylsilane system has been tested in the transformation of alcohols. The conversion to the corresponding halides and alkanes has been achieved in good yields and in the absence of solvent for a variety of substrates.

5,10-DIHYDRO-SILANTHRENE AS A REAGENT FOR THE BARTON-MCCOMBIE REACTION

Abstract The deoxygenation of secondary alcohols via thionoesters with the use of 5,10-dihydro-silanthrene as the radical reducing agent has been studied in detail. The ability of hydrogen donation of this silane has been measured using the one-carbon ring expansion of 1-(2-oxocyclopentyl)ethyl radical as a timing device.

Synthesis of 3-methylene-1,1-dichlorosilacyclobutane and 1,1-dichlorosilacyclopent-3-ene

Abstract : Silacyclobutanes have played an important role in the development of modern silicon chemistry. For example, silacyclobutanes serve as precursors to carbon-silicon double bonded intermediates silenes as well as to pentacoordinate silicon anions in the gas phase. Silacyclobutanes also undergo facile ring opening polymerization. Despite the importance of this ring system surprisingly few functionalized silacyclobutanes and silacyclobutenes have been prepared. Similarly, there is considerable interest in 1-silacyclo-pent-3-enes due to their facile conversion into other functionalized silicon heterocycles as well as due to their ability to undergo anionic ring opening polymerization. These compounds have usually been prepared by reaction of a 1,3-diene with a dihalosilane under dissolving metal reduction conditions. (jes)

Theory and application of photoelectron spectroscopy : XLIV. A quantitative account of hyperconjugation in allyl and benzyl compounds of elements of Group IVB

Abstract It is shown that the destabilization of the π-MOs in allyl and benzyl compounds of elements M of Group IVB can be quantitatively predicted on the basis of the hyperconjugative M—C/π interaction model.

Influence du Solvant sur une Reaction d'Heterocyclisation a Partir des Dichlorosilanes: Synthese de Nouveaux Sila-1 Cyclopentenes-3

Abstract The reaction between dichlorosilanes and conjugated dienes is closely dependent upon the metal and the solvent. New 1-silacyclopent-3-enes, with various substituents at the heteroatom, are prepared in good yield with Mg, THF and butadiene. For isoprene and dimethylbutadiene, a THF-HMPT mixture must be generally used to increase the ring closure reaction and to limit the competitive reaction of polymerisation to a low value.

Application des spectrographies RMN 13C et 1H a l'etude de derives cycliques du silicium et germanium, interactions pπdπ

Abstract The properties of 1-sila- and 1-gemma-cyclopent-2-(or -3-)enes with various substituents have been investigated by 13 C and 1 H NMR spectroscopies. Values of chemical shifts and coupling constants in olefinic cyclic systems and in aromatic or ethylenic substituents attached to the hereto atom suggest the presence of a mesomeric p π  d π interaction, particularly for the silicon atom. Studies at low temperatures given conformational data, which have been compared with data from the literature.

Synthese et reactivite de sila-1 cyclopentanols-2: formation d'oxa-1 sila-2 cyclohexanes par reaction d'extension de cycle

Abstract Three 1-silacyclopentan-2-ols, representative members of a new class of compounds, were prepared from the corresponding 1-silacyclopent-3-enes. These silacyclopentanols can, in particular, give rise to 1-oxa-2-silacyclohexanes by a ring expansion reaction.