Gérard Audran

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.

Straightforward Enantioselective Synthesis of Both Enantiomers of Karahana Lactone Using a Domino Ring-Closure Sequence

Abstract A straightforward enantioselective synthesis of both enantiomers of karahana lactone is described starting from enantiopure (R) or (S)-4-hydroxy-3-methyl-cyclohex-2-en-1-one. The key step of the sequence is an acid-induced domino reaction with three pathways running. Because of the first description of karahana lactone as a solid, the structure was secured by X-ray structural analysis.

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.

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.

Enantioselective Synthesis of 3-Methylcarbapentofuranose Derivatives, Based on a Chemoenzymatic Procedure

) was deter-mined by the ratio of the peak areas obtained by GC sep-aration on a chiral phase (see Exp. Sect.). The enantiomersof the remaining alcohol and those of the produced acetatewere perfectly separated. After 16 h at room temp., the act-ive enzyme was recovered for reuse by filtration. Concentra-tion of the filtrate and column chromatography on silica gelafforded 58% of the unreactive alcohol (1

ENANTIOSPECIFIC TOTAL SYNTHESIS OF BOTH ENANTIOMERS OF LAURENE BY A CHEMICAL DIASTEREOSELECTION/LIPASE-CATALYZED KINETIC RESOLUTION SEQUENCE

Abstract A short and efficient enantiospecific total synthesis of natural (+)-laurene and its enantiomer is described. The methodology was developed by employing a stereoselective H-ene reaction of an isocyclic allyltrimethylsilane with paraformaldehyde, followed by a lipase-mediated kinetic resolution of the racemic key intermediate.

Etude Cinétique de la Décomposition Radicalaire de la Liaison C-ON d’une Alcoxyamine : Effet de Solvant

The alkoxyamines (or trialkylhydroxylamines) R1R2NOR3 are very labile molecules able to undergo a homolytic rupture at physiological temperature to give a stable nitroxide radical for diagnostic applications and a highly reactive alkyl radical for therapeutic applications. In this work, we present the results of an alkoxyamine homolysis and the influence of solvent on this radical decomposition.