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. A series of substituted ferrocenyl boranes and boronic acids were synthesized. The oxidation to the corresponding ferrocenium derivatives provides access to strong Lewis acids as characterized by computational methods. The ferrocenium derivatives were active catalysts for the Lewis acid mediated Meinwald epoxide rearrangement and yielded predominantly the aldehydes as kinetic products.