Organosilanols as catalysts in asymmetric aryl transfer reactions

reaction: see text] Various ferrocene-based organosilanols have been synthesized in four steps starting from achiral ferrocene carboxylic acid. Applying these novel planar-chiral ferrocenes as catalysts in asymmetric phenyl transfer reactions to substituted benzaldehydes afforded products with high enantiomeric excesses. The best result (91% ee) was achieved in the addition to p-chlorobenzaldehyde with organosilanol 2b, which has a tert-butyl substituent on the oxazoline ring and an isopropyl group on the silanol fragment.