Multiple acetylation of pentaphenylferrocene – Synthesis and asymmetric reduction of 1-acetyl-1′,2′,3′,4′,5′-penta(para‐acetylphenyl)ferrocene

The Friedel–Crafts acetylation of pentaphenylferrocene has been revisited using 1.1 equivalents of AcCl/AlCl3 in CH2Cl2 at room temperature leading to the synthesis of 1‐acetyl‐1′,2′,3′,4′,5′‐pentaphenylferrocene (78 % yield). Increased quantities of reagents and longer reaction times resulted in acetylation of the phenyl groups exclusively at the para‐position, this methodology culminating in the synthesis of 1‐acetyl‐1′,2′,3′,4′,5′‐penta(para‐acetylphenyl)ferrocene (32 % for a two step process). Subsequent asymmetric reduction of all six ketone functionalities with BH3·SMe2 catalysed by 60 mol‐% (S)‐CBS proceeded in 81 % yield to give (R,R,R,R,R,R)‐1‐(α‐hydroxyethyl)‐1′,2′,3′,4′,5′‐penta[para‐(α‐hydroxyethyl)phenyl]ferrocene, a highly functionalised enantiopure building block for the synthesis of ligands and materials.