Yannick Vallée

Sc(BINOL)2Li: a new heterobimetallic catalyst for the asymmetric Strecker reaction

Abstract The new chiral heterobimetallic complex Sc(BINOL) 2 Li 1 was prepared and used as a catalyst in the enantioselective addition of a cyanide source (HCN or TMSCN) to several imines. High conversion rates and enantiomeric excesses (e.e.s) as high as 95% were obtained.

Asymmetric Strecker reactions of ketimines catalysed by titanium-based complexes

Abstract The asymmetric addition of TMSCN to a ketimine has been achieved by use of catalytic quantities of chiral titanium(IV) complexes. Fast conversions together with enantiomeric excesses as high as 59% have been achieved.

The Reactions of Nitrones with Indoles

Abstract The reaction of nitrones with various indole derivatives has been studied. When the reaction was promoted by ClSiMe3, the isolated products were 3,3′-diindolylalkanes. With HCl as the activating reagent, 3-indolylhydroxylamines were isolated. The diastereoselectivity of this condensation with a nitrone derived from cysteine was investigated. A method for the introduction of an alkylhydroxylamino group onto position 2 of indole, the synthesis of three natural 3,3′-diindolylalkanes and of non-symmetric diindolylalkanes are also reported.

The reaction of nitrones with indoles. Synthesis of asymmetrical diindolylalcanes

Abstract The reaction of nitrones with indoles in the presence of HCl gives indolyl N -hydroxylamines. In the presence of Me 3 SiCl symmetrical diindolylalcanes are obtained. A synthesis of asymmetrical diindolylalcanes and the syntheses of three natural symmetrical diindolylalcanes are reported.

The reaction of propiolate acetylides with nitrones. Synthesis of γ-amino-α,β-ethylenic acid derivatives

Abstract Nitrones react with the lithium anions of ethyl and t-butyl propiolates to give acetylenic N-hydroxylamines. The reduction of these compounds with Zn in the presence of an acid leads to E and Z α,β-ethylenic-γ-aminoacids derivatives. The stereoselectivity of these reactions was studied.

Cis-selectivity of the kinetic deprotonation of dithiopropanoates

Abstract Deprotonation of dithiopropanoates with LDA in THF solution at −78°C afforded chiefly the cis lithium thioenolate in contrast with the trans enolization of most of carbonyl compounds. The cis geometry was proved by a thio-Claisen rearrangement.

Diastereoselective addition of terminal alkynes to chiral nitrones: asymmetric synthesis of propargylic N-hydroxylamines

Abstract 1,3-Asymmetric induction in the Et2Zn-catalyzed addition of terminal alkynes was studied with nitrones bearing a chiral auxiliary on their nitrogen atom. The obtained propargylic N-hydroxylamines were generally isolated in good yields and with satisfactory to excellent diastereoselectivities.

Novel polyhydroxylated cyclic nitrones and N-hydroxypyrrolidines through BCl3-mediated deprotection.

A general method to prepare a new class of carbohydrate-derived, enantiomerically pure polyhydroxypyrroline N-oxides from their alkoxy (protected) derivatives is presented. Boron trichloride is shown to cleave efficiently benzyl ethers and ketals without affecting the imine N-oxide functionality of nitrones. The same reagent (BCl3) also allowed the efficient synthesis of a polyhydroxylated N-hydroxypyrrolidine, giving access to a novel class of N-hydroxyiminosugars.

Self-organization of ligands in multi-component titanium catalysts for the enantioselective ene reaction of glyoxylates

Abstract Addition of conformationally flexible biphenols to ( R )-BINOL–Ti(O i Pr) 2 , forms a new catalytic species with which ee s are as high as 97.3% in the hetero-ene reaction of n -butyl glyoxylate to α-methyl styrene.

Can chloramine-T be a nitrene transfer agent?

Abstract Reaction of chloramine-T and methyl p-tolyl sulfide to give the corresponding sulfimide appears to proceed via a nitrene transfer mechanism in the presence of a copper(I) catalyst and a second nitrogen ligand .