A NOVEL EASILY ACCESSIBLE CHIRAL FERROCENYLDIPHOSPHINE FOR HIGHLY ENANTIOSELECTIVE HYDROGENATION, ALLYLIC ALKYLATION, AND HYDROBORATION REACTIONS

The new ligand nylphosphino)ferrocenyl]ethyldicyclohexylphosphine ((R) -(S)-3a) was prepared in two steps from the commercially available N,N -dimethyl-(R)-1-ferrocenylethylamine via -1-[(S)-2-(diphenylphosphino) ferrocenyl]ethylamine ((R)-(S)-1) in good yields. The crucial second s tep, i.e., the substitution of the dimethylamino group by the dicycloh exylphosphino fragment, was achieved in 88% yield under complete reten tion of configuration in acetic acid solvent, using dicyclohexylphosph ine as a reagent. This methodology constitutes an easy access to a cla ss of chiral chelating diphosphines, where the two ligating moieties c an be varied independently from one another, thus allowing the study o f both the steric and electronic influence of the ligands on stereosel ectivity. Compound 3a was used in Rh-catalyzed asymmetric hydrogenatio n and hydroboration as well as in Pd-catalyzed allylic alkylation reac tions giving high enantioselectivities (up to 99%).