Jérôme Lacour

Recent developments in chiral anion mediated asymmetric chemistry.

Chemical reactions and processes often involve cationic prostereogenic or racemic reagents, intermediates or products. To afford instead non-racemic or enantiopure compounds, an asymmetric ion pairing of the cations with chiral anionic counterions can be considered. This review presents recent examples of the synthesis and use of chiral anions for stereoselective purposes.

Chiral anion-mediated asymmetric ion pairing chemistry

Chemical reactions and processes often involve cationic reagents, intermediates or products in prochiral or chiral racemic form. To afford instead non-racemic compounds, an asymmetric ion pairing of the cations with chiral anionic counterions can be considered. This review presents recent examples of the synthesis and use of chiral anions for such stereoselective purposes.

Mounting freestanding molecular functions onto surfaces: the platform approach.

A modular system has been developed to mount molecules upright onto metal surfaces in a well controlled geometry. The approach is based on a reactive platform (triazatriangulenium salt) with an electrophilic center. Functional molecules are attached via C-C bond formation. The distance from the surface can be varied by a spacer, and the distance of the functional units from each other by the size of the platform. Self-assembly of the parent triazaangulenium salt as well as the functionalized platforms on Au(111) surfaces results in stable, hexagonally ordered adlayers.

A Highly Configurationally Stable [4]Heterohelicenium Cation

Ein konfigurationsstabiles Heterohelicen: Uber die diastereomeren Salze mit dem phosphorhaltigen Anion binphat gelang die Trennung der Enantiomere eines [4](Hetero)heliceniumkations (siehe Bild: N=violett, O=rot). Die absoluten Konfigurationen wurde durch Messung des Schwingungscirculardichroismus bestimmt. Die Energiebarriere fur die Enantiomerisierung der Verbindung ist deutlich groser als beim [6]Helicen.

Self-assembled hexanuclear arene ruthenium metallo-prisms with unexpected double helical chirality

Self-assembly of 2,4,6-tripyridyl-1,3,5-triazine (tpt) subunits with arene ruthenium building blocks and oxalato bridges affords cationic triangular metallo-prisms of the type [Ru6(arene)6(tpt)2(C2O4)3]6+ (arene = C6Me6 and p-Pr(i)C6H4Me); the unexpected double helical chirality of the metallo-prisms observed in the solid state persists in solution giving rise to two different stereodynamic processes as demonstrated by NMR enantiodifferentiation experiments.

One-Step Synthesis of Nitrogen-Containing Medium-Sized Rings via α-Imino Diazo Intermediates

Eight- and 9-membered dioxazocines and dioxazonines are readily synthesized starting from N-sulfonyl-1,2,3-triazoles in a single-step procedure. A perfect regioselectivity and generally good yields (up to 92%) are obtained under dirhodium catalysis using 1,3-dioxolane and 1,3-dioxane as solvents and reagents.

Recent developments in enantioselective phase transfer catalysis using chiral ammonium salts

Due to the constant demand for non-racemic molecules in both industrial and academic laboratories, many efforts have been devoted in the last 25 years to the development of enantioselective phase transfer catalyzed (PTC) processes. Much of this chemistry was recently reviewed - the latest reports were from 2003/2004 and treated essentially the synthesis of non racemic a-amino acids. After a short historical introduction, this article will thus review enantioselective PTC reactions reported in the last three years (2003-2006) and demonstrate how broad and active the field is - and this considering ammonium-catalyzed reactions only.

Modular Synthesis, Orthogonal Post-Functionalization, Absorption, and Chiroptical Properties of Cationic (6)Helicenes**

Pick and choose: Novel cationic diaza-, azaoxo-, and dioxo[6]helicenes are readily prepared and functionalized selectively by orthogonal aromatic electrophilic and vicarious nucleophilic substitutions (see scheme). Reductions, cross-coupling, or condensation reactions introduce additional diversity and allow tuning of the absorption properties up to the near-infrared region. The diaza salts can be resolved into single enantiomers.

Diastereoselective Ion Pairing of TRISPHAT Anions and Tris(4,4'-dimethyl-2,2'-bipyridine)iron(II)

Two configurationally stable, chiral anions (TRISPHAT, 1) behave as efficient hosts that control the configuration of a configurationally labile iron(II) complex as the guest with high diastereoselectivity (>96 % de) upon ion pairing. The diastereoselectivity increases with decreasing solvent polarity.

Effect of the Medium on the Oxaziridinium-Catalyzed Enantioselective Epoxidation

TRISPHAT salts of chiral iminium cations allow, in combination with 18-C-6, the use of biphasic CH2Cl2/water conditions, which can improve the enantioselectivity of the oxone-mediated epoxidation.