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.