Stereoselective Synthesis of 1,1',2,2'‐Tetrasubstituted Ferrocenes by Double Lithiation of a 1,1'‐Disubstituted Ferrocenyl Pyrroloimidazolone.

A 1,1'‐disubstituted ferrocenyl pyrroloimidazolone with syn stereochemistry undergoes double lithiation–electrophile quench in a one‐pot procedure to give C2‐symmetric 1,1',2,2'‐tetrasubstituted products in >95 : 5 diastereomeric ratio (dr). These results represent an extension of double lithiation to access tetrasubstituted planar chiral ferrocenes for the first time to a nitrogen‐linked (pyrroloimidazolone) chiral directing group. The stereochemistry of the products was determined by X‐ray crystallography of distannane and dibromide adducts in combination with deuteration, elimination, and transmetalation experiments. Results support that products arise from selective deprotonation of the pro‐Sp position of each cyclopentadienyl (Cp) ring. [ABSTRACT FROM AUTHOR]