Sabine Choppin

First Regioselective C-2 Lithiation of 3- and 4-Chloropyridines

We have shown that the BuLi/LiDMAE reagent promotes the clean and regioselective C2 lithiation of 3- and 4-chloropyridines, while other reagents such as LDA or BuLi/TMEDA lead to classical ortho lithiation products or mixtures of regioisomers. The method was successfully applied to the preparation of various reactive 2,3- and 2,4-disubstituted pyridines.

Efficient and Stereoselective Access to the Polyol Fragment C9−C16 of Ansamycin Antibiotics

Efficient synthesis of the fragment C9-C16 bearing the anti,syn stereotriad of ansamycin antibiotics is described. Key steps for controlling the configuration of the three stereogenic centers involve a stereoselective Reformatsky-type reaction followed by a diastereoselective reduction of a beta-ketosulfoxide.

Efficient Synthesis of Vinylcycloalkylphenyl Sulfides from DME-Activated NANH2 Induced Intramolecular Dialkylation of Allylphenylsulfide

Abstract Vinylcycloalkylphenylsulfides have been prepared efficiently by a one-pot intramolecular dialkylation of allylphenylsulfide. The used basic reagent is constituted of a suspension of commercial NaNH2 in 1,2-dimethoxyethane as non-ionic activating agent.

ONE-POT DIALKYLATION OF ALLYLPHENYLSULFIDE INDUCED BY AMINOALKOXIDES-ACTIVATED NANH2. APPLICATION TO THE SYNTHESIS OF UNSYMMETRICAL KETONES

Abstract It is shown that the activation of NaNH2 by sodium aminoalkoxides, leading to new superbases, induced an efficient one-pot dialkylation of allylphenylsulfide. The regioselectivity of the reaction (α,α′ vs α,γ) was found as strongly dependent on the nature of the alkyl halide. As an application, α,γ dialkylated products were efficiently converted into the corresponding unsymmetrical ketones.

First activation of sodium amide by polymer-supported alkoxides and amino-alkoxides

Polystyrene-supported alkoxides and amino-alkoxides are shown to act as efficient and reusable activating agents of sodium amide. This constitutes an unprecedented example of heterogeneous activation in sodium carbanion chemistry.

FeCl3·6H2O/acetaldehyde, a versatile system for the deprotection of ketals and acetals via a transacetalization process

Mild and efficient catalytic deprotection of ketals/acetals mediated by FeCl3·6H2O/acetaldehyde has been described in this paper. The versatility and high chemoselectivity of the iron(III)/aldehyde system are demonstrated by a large scope of examples. Deprotected ketones/aldehydes are nearly quantitatively isolated after filtration over a pad of silica gel followed by evaporation of volatile by-products.

Access to Wieland–Miescher Diketone-Derived Building Blocks by Stereoselective Construction of the C-9 Quaternary Carbon Center Using the Mukaiyama Aldol Reaction

The Mukaiyama aldol reaction has been used to efficiently install a lateral chain at the C-9 position of the Wieland-Miescher ketone derivative 3 within two steps, representing a shortcut compared to that of the classical sequences. The treatment of the silylated enol ether 8 with a wide range of acetals in the presence of tin tetrachloride led to a the diastereoselective construction of the C-9 quaternary center of 33 new building blocks derived from the Wieland-Miescher ketone derivative 3.

Access to the Enantiopure Axially Chiral Cyclophane Isoplagiochin D through Atropo‐diastereoselective Heck Coupling

Macrocyclization is typically the key step in the syntheses of cyclophane-type natural products. Considering cyclophanes with axially chiral biaryl moieties, the control of atroposelectivity is essential with biological activity and is synthetically challenging. We report an atroposelective approach involving Heck cyclization, which for the first time enables the total synthesis of an enantiopure macrocyclic bis(bibenzyl), namely isoplagiochin D. An enantiopure sulfinyl auxiliary in the ortho position of a biaryl axis (still flexible) was used to induce an atropo-diastereoselective Heck coupling (up to 98 % de). The traceless character of the sulfinyl auxiliary enables the introduction of a hydroxy group to give the target molecule with 98 % ee as well.