Ar-BINMOLs with axial and sp~3 central chirality - Characterization, chiroptical properties, and application in asymmetric catalysis

摘要

2′-Hydroxy-1,1′-binaphthalene-2-(arylmethanol) (Ar-BINMOLs), a family of new 1,1′-binaphthalene-2,2′-diol derivatives, prepared by a [1,2]-Wittig rearrangement, are introduced as new chiral molecules for the study of the modes of supramolecular aggregation on the basis of ESI-MS, NMR spectroscopy, differential scanning calorimetry (DSC), and X-ray diffractometry. Characterization showed that Ar-BINMOLs exhibit different characteristics to BINOL and act as supramolecules due to hydrogen bonding and aromatic π-π/C-H???π interactions. In particular, CD measurements of chiral and racemic Ar-BINMOL 2a in solution and the solid state show a strong Cotton effect, which revealed that amplification of chirality was observed because of the formation of a chiral supramolecular oligomer derived from the racemic monomer. To this end, the Ar-BINMOLs were used as supramolecular auxiliaries to mediate the Michael reaction of anthrone to (E)-β-nitrostyrene and could give the Michael adduct with comparable enantioselectivities. In addition, the Ar-BINMOLs act as ligands to promote asymmetric 1,2-addition of diethylzinc to aldehydes, which resulted in excellent yields and enantioselectivities (up to >99.9% ee) in the reactions of diethylzinc with a broad range of aromatic aldehdyes. The chiroptical properties, as well asthe characterization of racemic and chiral Ar-BINMOLs by ESI-MS, NMR spectroscopy, differential scanning calorimetry (DSC), and X-ray diffractometry, and their applications in enantioselective 1,4-Michael addition and 1,2-addition as highly efficient chiral supramolecular catalysts and ligands are reported.