Denis Planchenault

Asymmetric metal carbene insertion into the SiH bond

Abstract α-Silyl-α-substituted acetic esters have been prepared in good yields and reasonable diastereoselectivities using an asymmetric metal carbene insertion into the Siue5f8H bond. Optically active 1,2-diols were then prepared after reduction of the ester and conversion of the Cue5f8Si bond into a Cue5f8OH bond.

Rhodium(II)-vinylcarbenoid insertion into the SiH bond. A new stereospecific synthesis of allylsilanes

Abstract Rh2(OAc)4 catalysed decomposition of vinyldiazocarbonyl compounds in the presence of organosilanes led stereospecifically to the corresponding allylsilanes in good yields. An asymmetric approach has also been considered as well as the extension of the methodology to the synthesis of other allylic systems.

Stereoselective synthesis of substituted tetrahydrofurans via selenoetherification of 2-silyl-3-alkenols. A study of allylic stereocontrol

Abstract 5-endo-trig selenoetherifications of substituted 2-silyl-3-alkenols gave tri- or tetrasubstituted 2,4- cis tetrahydrofurans in moderate to good yields with excellent diastereoselectivities. Opposite stereoselectivities were found with an analogous allylic diol. A transition state model has been proposed to rationalize this stereochemical outcome.

Synthesis of α-(Alkoxysilyl)acetic esters. A route to 1,2 diols

Abstract An easy route to α-(alkoxysilyl)acetic esters and their utilization is described. It involves a two-step sequence carried out in one pot: Rhodium catalyzed Si-H insertion of a carbenoid, generated by decomposition of N 2 CHCO 2 Et, followed by a nucleophilic attack onto the Si-Cl bond by an alcohol. Alkylation of the title esters, reduction of the ester function and finally oxidation of the C-Si bond provide a facile entry to 1,2-diols.

New agents of biaryl oxidative coupling in fluoro acid medium. VI. Application to the synthesis of phenolic bisbenzocyclooctadiene lignans

Abstract A systematic study of redox couples in fluoro acid medium has been carried out for the oxidative coupling of bisbenzocyclooctadiene lignan precursors. Tl2O3 and Re2O7 were found to be the more efficient reagents with precursors possessing methylenedioxy substituents for the former and only methoxy groups for the latter. Finally, oxidative coupling of a phenolic dibenzylbutane led to a mixture of two BBCODs, resulting from para and ortho coupling to the phenolic group.

A one pot synthesis of α-(alkoxysilyl)acetic esters

Abstract An efficient synthesis of α-(alkoxysilyl)acetic esters by Siue5f8H insertion of carbenes, generated by rhodium catalysed decomposition of diazoacetic esters, followed by nucleophilic displacement of Cl by ROH has been developed. Alkylation of these α-silyl carbonyls followed by Tamao oxidation of the Cue5f8Si bond allow an easy access to terminal diols.

Synthesis of non-phenolic bisbenzocyclooctadiene lignan lactones and aporphinic alkaloids, by oxidative coupling with new agents in fluoro acid medium. IV.☆

Abstract A systematic study of oxidants used in fluoro acid medium allowed us to increase notably the number of efficient reagents for the non-phenolic oxidative coupling of lignan and alkaloid precursors. If dibenzylbutanolide had no methylenedioxyle group, Re 2 O 7 and RuO 2 .2H 2 O were the most efficient. With a methylenedioxyle group, best results were obtained with Tl 2 O 3 , Mn(OAc) 3 .2H 2 O and Ce(OH) 4 . Finally, aporphines were obtained with good yields with Ce(OH) 4 , RuO 2 .2H 2 O and Fe(OH)(OAc) 2 .

Mechanism of metal-carbenoid insertion into the SiH bond

Kinetic investigations on the insertion of metal-carbenoid intermediates into the Siue5f8H bond have been carried out. A kinetic isotope effect of 1.5 was found and the plot of log kXkH vs σ for the reaction of arylsilanes with EDA, gave a straight line with ϱ =− 0.31. It was thus concluded that the insertion proceeds through a concerted pathway with development of a small positive charge at the silicon centre and a relatively early transition state.

Preparation of optically active α-silylcarbonyl compounds using asymmetric alkylation of α-silylacetic esters and asymmetric metal-carbene insertion into the SiH bond

Abstract Substituted α-silylacetic esters have been prepared in good yields and with reasonable diastereoselectivities by three different routes. The first two involved alkylation of the parent α-silylacetic ester enolates, with the chiral auxiliaries being present either on silicon or on the ester function. The third route involving asymmetric insertion of metal-carbenoids into the Siue5f8H bond was found to afford better diastereoselectivities, using pantolactone as chiral auxiliary.

Electrophilic 5-endo-trig cyclisations of 2-silyl-3-alkenols. A stereoselective route to polysubstituted tetrahydrofurans

Abstract Electrophilic 5-endo-trig cyclisations of allylsilanes have been carried out leading to tri- and tetrasubstituted tetrahydrofurans with reasonable yields and excellent diastereoselectivities. A rationalization of both the regio- and the stereoselectivity has been proposed. A silicon group having a thienyl fragment attached to the silicon has also been devised and was shown to be oxidized under both electrophilic and nucleophilic conditions.