Efficient Stereoselective Synthesis of o-Functionalized P-Chirogenic Phosphines Applied to Asymmetric Catalysis

The stereoselective synthesis of P-chirogenic o-halogenophenylphosphines and their use for the preparation of o-functionalized derivatives are reported. The key step of this synthesis is based on the reaction of a P-chirogenic secondary phosphine borane, previously prepared using ephedrine methodology, with n-butyllithium (1.2 equiv.) and 1,2-dihalogenobenzene. The reaction proceeds by addition of the phosphide borane to the benzyne generated in situ from 1,2-dihalogenobenzene by metal-halide exchange with the intermediate carbanion. The o-halogenophenylphosphine boranes were obtained with retention of configuration at the P-center and with enantioselectivities up to 99% ee. The free o-halogenophenylphosphines were applied for the preparation of various kinds of o-functionalized P-chirogenic phosphines useful in asymmetric catalyzed reactions.