Gilbert Léandri

ZnI2 Catalyzed [2+2] versus [3+2] cycloaddition of an allyltrimethylsilane with 3-butyn-2-one : Confirmation of a cyclobutene by-product formation

Abstract NMR experiments unequivocally show that the by-product obtained from the ZnI 2 -promoted reaction of an allyltrimethylsilane with 3-butyn-2-one is a [2+2] cycloaddition compound. This fact corroborates our previously described assignment. In the experimental conditions used, the reaction occurs without 1,2-silyl shift.

Regioselective catalysed H-ene reaction of allylsilanes with 3-butyn-2-one application to a new synthesis of (±)-γ-ionone

Abstract An unexpected ZnI2 catalysed regioselective H-ene reaction between allysilanes and butynone in the presence of molecular sieves 4A is reported. The silyl group dramatically enhanced the rate of the reaction which is used as a key for a new synthesis of (±)-γ-ionone.

Nouvelle cyclopentannélation regiosélective par une séquence tandem ouverture electrophile/cycloaddition [3+2] entre cétones méthylènecyclopropaniques et l'allyltriméthylsilane

Abstract The TiCl 4 -mediated reactivity of five complementary substituted methylenecyclopropyl ketones with allyltrimethylsilane has been studied. The regioselectivity of the reaction, which affords functionalized methylene and/or alkylidenecyclopentanes in good yields, depends on the substitution of the cyclopropanic carbon α to the carbonyl function. The reaction occurs via a stereoselective cleavage of the carbocycle followed by a tandem [3+2] cycloaddition of the resultant ( Z )-1,3-zwitterion with allyltrimethylsilane that acts as the 1,2-partner in a synclinal approach.

CHEMO- AND REGIOSELECTIVITY IN THE LEWIS ACID-INDUCED REACTION OF STERICALLY UNHINDERED ISOCYCLIC ALLYLSILANES WITH 3-BUTYN-2-ONE

Abstract The primordial influence of the ring size in the Lewis acid-promoted reaction of sterically unhindered isocyclic allylsilanes with 3-butyn-2-one is reported. In all the cases, the classical Sakurai-Hosomi reaction is, for the most part or fully, suppressed. With cyclohexanic frameworks, allyltrimethylsilanes like 1a-c afford mainly or solely H-ene components. This chemoselectivity is quite different from the one of cyclopentanic core compounds 1d-f which act primarily as [2 + 2] cycloaddition agents at the expense of the H-ene products procedure. Furthermore, the regioselectivity of the H-ene products formation is opposite for the two skeletons. Using Me 2 AlCl, the [2 + 2] cyloaddition of five carbon atoms isocyclic allylsilanes proceeds with complete chemoselectivity and provides an efficient synthesis of functionalized bicyclo [3. 2. 0] heptenes.

A novel cyclopentane annulation by [3+2] cycloaddition of substituted methylenecyclopropyl ketones with allyltrimethylsilane

Abstract Reaction of subtituted methylenecyclopropyl ketones with allyltrimethylsilane affords functionalized methylene or alkylidenecyclopentanes in good yield via a TiCl 4 mediated cleavage of the carbocycle followed by a [3+2] cycloaddition of the resultant 1,3-zwitterion with allyltrimethylsilane which acts as the 1,2-partner.

Patchouli Fragrance Chemistry: Stereoselective Synthesis of (±)-ISO-Norpatchoulenol

Abstract A short and efficient stereoselective synthesis of (±)-iso-norpatchoulenol 3 involving, as a key step, the intramolecular trapping of a vinyl carbanion is described. The new compound has a weak characteristic odor of patchouli.

Réactivité de l'allyltriméthylsilane avec les acétylcyclopropanes en présence d'acide de Lewis

Abstract In the presence of Lewis acid, allyltrimethylsilane undergoes 1,2-addition to the carbonyl system of acetylcyclopropanes. A second direct attack of the nucleophilic reagent on the transient cyclopropylcarbynyl cation formed yields diallylic and functionalised cyclohexane derivatives.

Etude de la réactivité de l'allyltriméthylsilane avec les cétones α-cyclopropaniques en présence de tétrachlorure de titane

Abstract The reaction of diversely substituted α-cyclopropylketones with allyltrimethylsilane in the presence of titanium tetrachloride has been studied. The products formation is explained by the intervention of a cyclopropycarbinyl transient cation formed after a first 1,2-addition on the carbonyl. With regard to the structure of the starting compounds, this intermediate reacts with a second molecule of allylsilane, either by a bimolecular addition on the carbocycle, or by the direct attack on the carbon bearing the formal positive charge yielding diallyl and functionalised cyclohexane derivatives. A general mechanism is proposed.