Catalytic enantiotopic-group-selective cross-couplings of achiral geminal bis(pinacolboronates) provide a route for the construction of nonracemic chiral organoboronates. In the presence of a chiral monodentate taddol-derived phosphoramidite ligand, these reactions occur with high levels of asymmetric induction. Mechanistic experiments with chiral 10B-enriched geminal bis(boronates) suggest that the reaction occurs by a stereochemistry-determining transmetalation that occurs with inversion of configuration at carbon.

No abstract

A novel transition-metal-catalyzed rearrangement of silylated cyclopropenes to the corresponding allenes is described. The presence of both the trimethylsilyl group on the cyclopropene and the platinum catalyst are crucial for this rearrangement.

Teaching new tricks to an old dog: By intercepting adducts between ketones and lithium trimethylsilyldiazomethane, a new Tiffeneau-Demjanov type methylene homologation could be realized in a single-step operation. Among proton sources and Lewis acids, silica gel was found to be the most effective reagent for the protonation of intermediates and their subsequent ring expansion (see scheme).

Recently, starch nanoparticles have attracted widespread attention from various fields. In this study, a new strategy for preparing covalent-cross-linked starch nanoparticles was developed using boron ester bonds formed between debranched starch (DBS) and borax. The nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffraction (XRD), dynamic light scattering (DLS), differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). The obtained nanoparticles were spherical with a size of 100−200 nm. The formation of boron ester bonds was confirmed by FTIR. The as-prepared starch nanoparticle exhibited a low relative crystallinity of 13.6%−23.5%. Compared with pure starch film, the tensile strength of starch film with 10% starch nanoparticles increased about 45%, and the elongation at break percentage of starch film with 5% starch nanoparticles increased about 20%. The new strategy of forming starch nanoparticles by using boron ester bonds will advance the research of carbohydrate nanoparticles.