Synthesis of Chiral Carbocations Linked to a Ferrocene Unit

Orthosubstituted ferrocene carboxaldehydes (100% ee) were transformed into carbinols by addition of a Grignard reagent. Treatment by strong acids (HPF6, CF3SO3H, etc) gave isolated chiral carbocations which are good Lewis acid catalysts for various reactions such as Diels-Alder reaction. Chiral carbocations linked to a planary chiral ferrocene unit were prepared starting from enantiopure α-substituted ferrocene aldehydes.