Selective Functionalization of Chiral Ferrocenyl Acetals. Easy Access to Various Tri- and Tetrasubstituted Ferrocenes with Controlled Geometry

The lithiation of 2-substituted chiral dioxane 2, followed by electrophilic trapping of the lithiated intermediate, yields various 1,5-disubstitued acetals with good yields and excellent control of the geometry. These acetals can be easily hydrolyzed into various 1,5-disubstitued ferrocenecarboxaldehydes (in an enantiomerically pure form if the two substituents are different), which can be furthermore substituted on the other Cp ring to yield unprecedented 2,5,1‘-ferrocenecarboxaldehydes (in an enantiomerically pure form if they are chiral). The three substituents on ferrocenecarboxaldehyde can be different: this is, to the best of our knowledge, the first example of enantiomerically pure 1,2,3,1‘-tetrasubstituted ferrocene with planar chirality only.