A Versatile Organocatalytic Approach for the Synthesis of Enantioenriched gem-Difluorinated Compounds.

The combination of a practical and highly enantioselective organocatalytic reaction, which allows the stereoselective introduction of a benzodithiol group, with a fluorination step, gives a new and effective strategy for the stereoselective synthesis of difluorinated building blocks. The benzodithiol group is a versatile and chameleonic group that can be further functionalized before fluorination, giving customized and tailored useful synthetic strategies. As an example of the application of this facile strategy, the effective enantioselective synthesis of difluoroarundic acid is described.

Tetra-phosphonate calix[4]pyrrole cavitands as multitopic receptors for the recognition of ion pairs.

The synthesis, structural characterization, and binding properties of two unprecedented multitopic receptors for ion-pair recognition are described. We isolated two of the six possible diastereomeric deep cavitand receptors resulting from the installation of four phosphonate groups at the upper rim of a calix[4]pyrrole-resorcin[4]arene hybrid scaffold. The isolated tetra-phosphonate receptors display either three (iooo) or four (oooo) of their P═O groups oriented away from the deep and functionalized aromatic cavity.

A practical and stereoselective organocatalytic alkylation of aldehydes with benzodithiolylium tetrafluoroborate.

Recently, the direct substitution of allylic, benzylic, and tertiary alcohols has been achieved via SN 1-type reactions with catalytic amounts of Brønsted or Lewis acids. When a new stereogenic center is formed most of these transformations produce the desired product as a racemate, as these reactions proceed through carbenium ions. The arsenal of activation modes available in organocatalysis can be used to set up suitable reaction conditions in which chiral nucleophiles (enamine catalysis) or chiral electrophiles (iminium catalysis, chiral counterion catalysis) can easily be generated.

An overlooked yet ubiquitous fluoride congenitor: binding bifluoride in triazolophanes using computer-aided design.

Despite its ubiquity during the binding and sensing of fluoride, the role of bifluoride (HF2(-)) and its binding properties are almost always overlooked. Here, we give one of the first examinations of bifluoride recognition in which we use computer-aided design to modify the cavity shape of triazolophanes to better match with HF2(-). Computational investigation indicates that HF2(-) and Cl(-) should have similar binding affinities to the parent triazolophane in the gas phase.

Switching from separated to contact ion-pair binding modes with diastereomeric calix[4]pyrrole bis-phosphonate receptors.

We describe the design, synthesis and conformational assignment of three diasteromeric bis-phosphonate cavitands based on an aryl extended calix[4]pyrrole tetrol scaffold. The diastereoisomers differ in the relative spatial orientation of the P═O groups installed at their upper rims. We demonstrate that these compounds act as heteroditopic receptors for ion pairs forming ion-paired 1:1 complexes with alkylammonium (quaternary and primary) chloride salts in dichloromethane (DCM) solution and in the solid-state.