Tricarbonyliron(0) complexes of bio-derived η4 cyclohexadiene ligands: An approach to analogues of oseltamivir

We have prepared novel [η4] and [η5]+ tricarbonyliron complexes from an unusual enantiopure cyclohexadiene ligand that possesses a quaternary stereocentre; this in turn is prepared through biotransformation of an aromatic ring. The cyclohexadiene ligand initially possessed two hydroxyl groups, both of which could be substituted with other functionality by means of an overall [η4] → [η5]+ → [η4] → [η5]+ → [η4] sequence. From six novel tricarbonyliron complexes which have been prepared, three have been characterised by x-ray crystallography. The reaction sequence we describe is potentially of relevance to the synthesis of analogues of the anti-influenza drug oseltamivir. In addition, the failure of an attempted addition of a bulky nitrogen nucleophile to an [η5]+ complex sheds light on the limits of reactivity for such additions. Thus, two bulky nucleophiles which are each known to add successfully to unencumbered [η5]+ complexes seemingly cannot be added sequentially to adjacent positions on the cyclohexadiene ligand