C2-Symmetric 1, l',2,2'-tetrasubstituted ferrocene derivatives are prepared in high yields from chiral 1,1'-bis(oxazolinyl)ferrocenes v/a diastereoselective o,o'-dilithiation with sec-butyUithium followed by nucleophilic substitution. 1, l'-Bis(oxazolinyl)ferrocenes were prepared from 1,1 '-ferrocenedicarbonyl dichloride and enantiomerically pure aminoalcohols via the corresponding bis(~-hydroxylamide)s and dimesylates as intermediates.
Planar chirality of ferrocene has found increasing importance for metal-catalyzed asymmetric organic synthesis in recent years.1 For the purpose of developing novel ferrocene ligands with planar chirality, several research groups have recently studied the diastereoselective ortho-lithiation of ferrocenyl methyl amine, 1 ferrocenyl acetals, 2 ferrocenyl sulfoxides, 3 and especially ferrocenyl oxazolines.' However, C2-symmetric ferrocene ligand with planar chirality has not received much attention until now. Hayashi and co-workers reported an example of C2-symmetric 1,1 ',2,2'-tetrasubstituted ferrocene chiral ligand I with which an excellent enantiomeric excess was achieved for the coupling reaction of vinyl bromide and 1-phenylethylzinc chloride. 5
For the preparation of 1, however, a resolution procedure was needed.
We here report the highly diasma'coselective o,o'-dilithiafion of 1,1' -bis(oxazolinyl)ferrocene 5, leading to the synthesis of novel C2-symmetric 1,1',2,2'-tetrasubstituted ferrocene, as well as the preparation of 1,1'bis(oxazolinyl)ferrocene 5. Thus, by the dilithiation of bis(oxazolinyl)ferrocene with sec-butylfithiurrt followed by the reaction with eleetrophiles, novel C2-symmetric 1, l',2,2'-tetrasubstimted fea'rocene derivatives were obtained in high yields with ease, only requiring purification using silica gel column chromatography, rather than by resolution. Park and co-workers' have recently published very similar work but with different results