Preparation and Resolution of a Modular Class of Axially Chiral Quinazoline-Containing Ligands and Their Application in Asymmetric Rhodium-Catalyzed Olefin Hydroboration

The preparation and resolution of a series of axially chiral quinazoline-containing ligands is
described in which the key steps are the metal-catalyzed naphthyl-phosphorus bond formation,
the naphthalene-quinazoline Suzuki coupling, and the preparation of the Suzuki electrophilic
components from the corresponding imidate and anthranilic acid. Diastereomeric palladacycles
derived from the racemic phosphinamines and (+)-di-μ-chlorobis[(R)-dimethyl(1-(1-naphthyl)ethyl)aminato-C2,N]dipalladium(II) were separated by fractional crystallization. The configuration of the
resulting diastereomers was determined by X-ray crystallographic analysis. Displacement of the
resolving agent by reaction with 1,2-bis(diphenylphosphino)ethane afforded enantiopure ligand in
each case. Their rhodium complexes were prepared and applied in the enantioselective hydroboration
of a range of vinylarenes. The quinazolinap catalysts were found to be extremely active, giving
excellent conversions, good to complete regioselectivities, and the highest enantioselectivities
obtained to date for several members of the vinylarene class, including cis-β-methylstyrene (97%),
cis-stilbene (99%), and indene (99.5%).