Modular Synthesis of Ar-BINMOL-Phos for Catalytic Asymmetric Alkynylation of Aromatic Aldehydes with Unexpected Reversal of Enantioselectivity

An interesting group of multifunctional phosphines (Ar-BINMOL-Phos; Ar-BINMOL=1,1-binaphthalene-2--arylmethanol-2-ol) with multi-stereogenic centers of axial and sp3-central chirality has been prepared successfully from a single chiral source through a concise synthetic route, in which the neighbouring lithium-promoted [1,2]-Wittig rearrangement proceeding with excellent diastereoselectivity and enantioselectivity is the key process in this approach. Also, in the catalytic alkynylation of aromatic aldehydes with terminal alkynes, the combination of these Ar-BINMOL-Phos ligands with dimethylzinc was found to be an effective catalyst system to afford predominantly the S-configured propargylic alcohols, whereas the additional use of calcium hydride and n-butyllithium along with the same Ar-BINMOL-Phos ligands gave the R-configured products in high yields and excellent enantioselectivities (up to >99% ee).