Honoré Monti

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.

Use of lipase-catalyzed kinetic resolution for the enantioselective approach toward sesquiterpenes containing quaternary centers: the cuparane family

The enzymatic kinetic resolution of a suitable hydroxylated precursor of the deoxygenated molecule 3, a key intermediate in a synthesis of the cuparane skeleton, was investigated by screening a range of lipases for enantioselective transesterification with vinyl acetate. CAL-B proved to be the best lipase, affording both enantiomers in high enantiomeric excess (>98% ee). Single-crystal X-ray diffraction analysis enabled assignment of the absolute configuration and the enantiospecificity of the tested lipases.

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.

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.

A stereocontrolled approach towards highly oxygenated taxane C and CD-ring precursors

Abstract Based upon a remarkable β-face diastereoselection, a stereocontrolled construction of bicyclic systems with the appropriate stereochemical disposition of the substituents belonging either to a Baccatin-I C-ring precursor or a Taxol® CD-ring precursor is reported.

First enantioselective total synthesis of both enantiomers of lancifolol. Correlation: absolute configuration/specific rotation

Abstract The first enantioselective total synthesis of both enantiomers of lancifolol has been accomplished using a Z -stereoselective Peterson olefination and a palladium-catalyzed cross-coupling reaction as key steps. This approach allows us to correlate the relationship between absolute configuration and specific rotation, to date both unknown.