[Sulfonylbis(bromomethylene)]dibenzene

The title compound, C14H12Br2O2S, crystallizes as the meso isomer of a diastereoisomeric pair. This structure determination was key to determining that the 1,3 elimination of bromine by triphenylphosphine occurs with inversion of the configuration at each of the two chiral carbon atoms. In the crystal, the molecules are linked by weak C—H...O and C—H...Br hydrogen bonds.

Regio- and enantioselective umpolung gem-difluoroallylation of hydrazones via palladium catalysis enabled by N-heterocyclic carbene ligand

The enantioselective construction of C–CF2R (R: alkyl or fluoroalkyl) bonds has attracted the attention of synthetic chemists because of the importance of chiral fluorinated compounds in life and materials sciences. Catalytic asymmetric fluoroalkylation has mainly been realized under organocatalysis and Lewis acid catalysis, with substrates limited to carbonyl compounds. Few examples using transition-metal catalysis exist, owing to side reactions including decomposition and isomerization of fluoroalkylating reagents. Herein we report umpolung asymmetric difluoroallylation of hydrazones with 3-bromo-3,3-difluoropropene (BDFP) under palladium catalysis. Difluoroallylation products having quaternary chiral carbon centers are afforded in good yields with high α/γ- and enantioselectivities. The usefulness of the reaction products is demonstrated and an inner-sphere mechanism of the reaction is proposed. The use of chiral N-heterocyclic carbene as ligand is the key for the selectivities as well as the productivity of the reaction.

The Underexplored Field of Lanthanide Complexes with Helicene Ligands: Towards Chiral Lanthanide Single Molecule Magnets

The effective combination of chirality and magnetism in a single crystalline material can lead to fascinating cross-effects, such as magneto–chiral dichroism. Among a large variety of chiral ligands utilized in the design and synthesis of chiral magnetic materials, helicenes seem to be the most appealing ones, due to the exceptionally high specific rotation values that reach thousands of deg×cm3×g−1×dm−1, which is two orders of magnitude higher than for compounds with chiral carbon atoms. Despite the sizeable family of transition metal complexes with helicene-type ligands, there are only a few examples of such complexes with lanthanide ions. In this mini-review, we describe the most recent developments in the field of lanthanide-based complexes with helicene-type ligands and summarize insights regarding the further exploration of this family of compounds towards multifunctional chiral lanthanide single molecule magnets (Ln-SMMs).

EVALUATION OF ANOMERICRECOGNITION IN GALACTOSE BINDING LECTINS USING CROSSLINKED HEMICELLULOSE: A COMPARATIVE STUDY THROUGH AFFINITY CHROMATOGRAPHY

The isolation of lectins by affinity chromatography with crosslinked hemicelluloses has been a common practice because of the variety of glycosides that they present, improving the isolation of different kinds of lectins, such as the galactose ligands.Lectins affinity for carbohydrates is so specific that a simple configuration of the chiral carbon can affect affinity, and there are lectins that are more related to alfa-galactosidic than beta-galactosidic residues, setting up that way, an anomeric recognition.The anomeric configuration of galactose residuesseems to have biological importance related to the behavior of some diseases and physiological processes. This work aimed to assess the anomeric recognition of two lectins reported as β-galactose ligands (PNA and ricin) and two lectins reported as α-galactose ligands (frutalin and jacalin) in two types of hemicellulose (xyloglucan of Tamarindus indica and galactomannan of Caesalpinia pulcherrima), subsequently crosslinked and used as chromatographic matrices. As a result,chromatographic profiles and retained fractions suggested preferential anomeric recognition by lectins for the hemicelluloses crosslinked. The galactomannan matrix retained 0,5mg of PNA lectin and 2,3mg of ricin lectin; meanwhile, the xyloglucan matrix retained 3,4mg of PNA and 3,2mg of ricin; results obtained by applying 5 mg of lectin. Ricin expresses a visible flexibility in anomeric recognition, while PNA shows a restricted recognition of β-galactose residues.Frutalin and jacalin did not show recognition of the xyloglucan matrix. This work proposes using hemicellulose reticles with epichlorohydrin as affinity chromatographic matrices for anomeric studies on recognizing galactose binding lectins.