Synthesis of Ferrocenyl Boranes and their Application as Lewis Acids in Epoxide Rearrangements

A series of substituted ferrocenyl boron derivatives was synthesized. The oxidation of the ferrocenyl unit resulted in a significant increase of the boron-centered Lewis acidity. The neutral and cationic Lewis acids were characterized by NMR-spectroscopy, crystal structure analysis and by computational methods. The new Lewis acids were then applied in the Meinwald rearrangement of epoxides, predominantly furnishing aldehydes as the kinetic products.