Chiral Carborane Acids Decorated with Binol-Based Phosphonates: Synthesis, Characterization, and Application.

The syntheses of hexabrominated closo-carborates decorated with different chiral Binol-derived phosphonates and their conjugate acids are described. X-ray diffraction analysis reveals a polymeric structure for the sodium salt with the anionic units connected by [B-Br-Na-O═P]+ linkages. For the acid, coordination of the proton to the phosphonate's P═O oxygen atom is assumed. The pKa value was estimated by combining experiments and computations. Application of these Brønsted acids as chiral catalysts in an imino-ene and a Mukaiyama-Mannich reaction was moderately successful.

Atroposelective Silylation of 1,1'-Biaryl-2,6-diols by a Chiral Counteranion Directed Desymmetrization Enhanced by a Subsequent Kinetic Resolution.

A desymmetrizing silylation of aromatic diols is reported. The previously unknown asymmetric silyl ether formation of phenol derivatives is achieved by applying List's counteranion directed silylation technique. A silylium-ion-like silicon electrophile generated from an allylic silane paired with an imidodiphosphorimidate (IDPi) enables enantioselective discrimination of achiral 1,1'-biaryl-2,6-diols. The enantioselectivity of that desymmetrization is further improved by a downstream kinetic resolution, converting the monosilylated minor enantiomer into the corresponding, again achiral bissilylated diol.