Synthesis of Ar‐BINMOL Ligands by [1,2]‐Wittig Rearrangement to Probe Their Catalytic Activity in 1,2‐Addition Reactions of Aldehydes with Grignard Reagents

Abstract We have demonstrated a highly diastereoselective synthesis of optically pure Ar‐BINMOL‐derived diols and their analogues. The present study demonstrates a unique cascade chirality transfer in a [1,2]‐Wittig rearrangement that leads to chiral diols with three stereogenic centers, which include a chiral sp 3 center at the alcohol and C 2 ‐axial chirality. Screening these ligands in the arylation of aromatic aldehydes with Grignard reagents shows that the naphthyl‐substituted BINMOL promotes the aryl transfer reaction in good yields (70–92 %) and moderate‐to‐good enantioselectivities (up to 72 % ee ), and a series of control experiments substantiates that the axial chirality and the chiral sp 3 center at the alcohol of the Ar‐BINMOLs are the pivotal enantioselectivity‐controlling structure elements. In addition, this study demonstrated the importance of the chiral sp 3 center at the alcohol on Ar‐BINMOL for the aryl transfer reaction. Finally, we found that the chiral Ar‐BINMOL ligand 2h mediated the titanium‐promoted 1,2‐addition of MeMgBr to aldehydes to give the desired products in good yields with excellent enantioselectivities (up to 92 % ee ).