The preparation, resolution and chemistry of 1-(3,6-dimethylpyrazin-2- yl)(2-naphthyl)diphenylphosphine, an axially chiral phosphinamine

Article abstract of DOI:10.1016/S0040-4020(99)00066-6

A five step synthesis of the title compound in good yield is described. The biaryl linkage was formed in a Pd-catalyzed coupling of 2-chloro-3,6- dimethylpyrazine 10 with 2-methoxy-1-naphthylboronic acid 9. Demethylation of the product ether 11 afforded alcohol 12 which was converted into the corresponding triflate 13 by treatment with triflic arthydride. A Ni- catalyzed phosphinylation gave the required phosphinamine ligand 7 as a racemate. Diastereomeric palladacycles 16, formed from 7 and (+)-di-μ- chlorobis[(R)-dimethyl(1-(1-naphthyl)ethyl)aminato-C₂,N]dipalladium (II) 15 were separated, after considerable effort, to give diastereomerically pure 7. Displacement of the resolving agent by reaction with 1,2- bis(diphenylphosphino)ethane gave enantiopure 7. At ambient temperature this ligand was found to racemise.