Asymmetric synthesis of metallocenes through enantioselective addition of organolithium reagents to 6-(dimethylamino)fulvene.
Enantioselective addition of aryllithiums 2a-d (Ar = Ph (a), 2-MeC(6)H(4) (b), 2-MeOC(6)H(4) (c), 1-naphthyl (d)) to 6-(dimethylamino)fulvene (1) in the presence of (-)-sparteine in toluene at -78 degrees C generated chiral cyclopentadienyllithiums (4) substituted with an N,N-dimethylamino(aryl)methyl group, where the enantioselectivities are 51, 91, 90, and 83% for 4a, 4b, 4c, and 4d, respectively. Treatment of the chiral cyclopentadienides 4 with FeCl(2) or Fe(acac)(2) gave ferrocenes, which contain an N,N-dimethylamino(aryl)methyl side chain on both of the cyclopentadienyl rings. The enantiomeric purity of the chiral ferrocenes 7 thus obtained is 99% ee or higher for those containing a 2-MeC(6)H(4) (7b) or a 2-MeOC(6)H(4) (7c) group.
Suzuka
Toshimasa
T
Department of Chemistry, Graduate School of Science, Kyoto University, Sakyo, Kyoto 606-8502, Japan.
Ogasawara
Masamichi
M
Hayashi
Tamio
T