A NEW STEROSELECTIVE APPROACH TO CHIRAL FERROCENYL LIGANDS FOR ASYMMETRIC CATALYSIS

Optical active 6-(dialkylamino)fulvenes, derived from (R)-(1-phenylethyl)amine, (R)-(1-cyclohexylethyl)amine, and O-methylephedrine, respectively, were used to prepare chiral cyclopentadienyl synthons. The addition of MeLi to these fulvenes, affording the corresponding dialkyl(1-cyclopentadienylethyl)amines, was found to occur with high diastereoselectivity, the maximum being 87%, which was obtained with a fulvene derived from (R)-(1-cyclohexylethyl)amine. The reaction of the resulting cyclopentadienyllithium salt with the Cp*Fe-II- and MeCpFe(II)-fragments (generated in situ from [Fe(acac)(2)](n)) afforded th diastereomerically enriched heteroleptic ferrocenyl amines. These were converted by reaction with HNMe(2) in acetic acid to the corresponding optically active (75% ee) dimethylamino derivatives (S)-7 and (S)-16, respectively. Diastereospecific lithiation with BuLi and reaction with CIPPh(2) of the last tow compounds gave the phosphines (S)-(R)-9 and (S)-(R)-17. Retentive substitution of the dimethylamino group using dicyclohexylphosphine, 9-phosphabicyclo[3.3.1]nonane, pyrazole, or 3,5-dimethylpyrazole in acetic acid afforded the corresponding P,P- and P,N-chelating ligands, which were obtained optically pure after recrystallization. The optical purity was checked by HPLC using a chiral stationary phase. The absolute configuration at the newly formed stereogenic center was determined to be S by an X-ray crystallographic study of the pyrazole derivative (S)-(R)-Cp*FeC5H3CH(ME)-(N2C3H3)PPh(2))-1,2((S)-(R)-13). Crystals of (S)-(R)-13 are orthorhombic, space group P2(1)2(1)2(1), with a = 8.586(4) Angstrom, b = 16.224(9) Angstrom, c = 20.054(2) Angstrom, and Z = 4. Crystals of racemic Cp*FeC5H3CH(Me)((PC8H14)PPh(2))-1,2((S*)-(R*)-(R*)-12 are triclinic, space group P $($) over bar$$ 1, with a = 11.265(4) Angstrom, b = 11.666(4) Angstrom, c = 13.870(4) Angstrom, and Z = 2.