Development of a convenient new synthetic route to [3]ferrocenophanones

[3]Ferrocenophanone rac-8 was prepared by several non-Friedel–Crafts pathways starting from a Mannich-type coupling of 1,1′-diacetylferrocene followed by catalytic hydrogenation. Hydride abstraction from the resulting α-dimethylamino[3]ferrocenophane rac-14 with B(C₆F₅)₃ followed by hydrolysis gave the ketone rac-8. Several variants of the Sommelet reaction, using ethylglyoxylate, formaldehyde or hexamethylenetetramine (urotropine) as the “oxidizing” reagent gave the α-[3]ferrocenophanone 8 in good to excellent yield. Some variants of these reactions were also used for the preparation of the pure enantiomer (R)-8. The electrochemical behaviour of 8 has been investigated and compared with related derivatives.