The Synthesis Of Ar-BINMOL-derived Salan Ligand And Its Applications In Asymmetric Synthesis Reactions

Chiral BINOL and its derivatives in asymmetric catalysis have been reported in the past decades, and have found to be functionalized as versatile ligands for many asymmetric catalytic reactions. The Ar-BINMOL ligands are first designed and synthesized in our group. The BINOL backbone-based Ar-BINMOL ligand has the unique C2axis center and Sp3hybridized carbon center of secondary alcohols, which have been applied as efficient chiral ligands in various organic transformations. On the basis of previous studies in our groups, we continue to design and prepare a novel Ar-BINMOL-derived salan ligands for organic transformations, including organosilcon compounds-involved reactions.First, we synthesis the Ar-BINMOL-derived Salan ligand by several steps, and then studied the physic and chemical properties of this salan ligand. We detected the coordination of various metals to this salan ligand with UV-Vis and FL analysis, which proved that CuCl, AgOAc and BiCl3exhibit very strong fluorescence intensity and revealed high selectivity for Cu+, Ag+, Bi+ions compared with other metal ions. On the basis of FL analysis and ESI-MS spectra, we speculate that the noncovalent interactions or chelation enhancement between ligand with CuCl induced a conformation change upon the π-π stacking of aromatic rings and hydrogen bonding of-OH with-NH to promote the happening of fluorescence resonance energy transfer pairs. These findings promoted us to investigate the catalytic activity of salan-copper complex in various reactions.Second, the chiral salan ligand derived from chiral Ar-BINMOL was used in Cu-catalyzed Henry reaction. In this model reaction, the unique Salan ligand bearing a large aromatic π-wall led to an interesting and remarkable discrimination of different aldehydes, which may be due to noncovalent interactions involving aromatic π-π stacking interactions and hydrogen bonding between the copper ligand and aldehydes. In addition, the Cu complex could discriminate benzaldehyde and halide-con-taining aromatic aldehydes from methyl-, methoxy-, hydroxy-, and nitro-substituted aromatic aldehydes as well as aliphatic aldehydes.Last, we have demonstrated successfully that the salan-Cu catalyzed silyl-Reformatsky reaction of aromatic aldehydes with α-trimethylsilylmethylacetate (TMSMA) led to the highly efficient synthesis of β-hydroxyesters in high yields (up to98%). The synthetic method described in this reaction is also a very mild and effective procedure for the high-yielding synthesis of various aldol products (β-hydroxyesters).