Selective Carbonyl Reduction

Abstract

This paper reports studies directed toward the chemoselective reduction of ketones via an ?6 ruthenium—arene activating substituent. Due to the electron-donating aryl ring in phenyl ketones, the carbonyl has a lower partial charge; resulting in reduced electrophilicity compared to other non-conjugated carbonyls in the structure. However, when the arene portion is bound to a cationic 6-ruthenium complex, the electron density is inductively pulled away from the phenyl ketone moiety causing the partial charge to become greater. Due to the increased partial charge, chemoselective nucleophilic attack on this carbonyl should occur more readily compared to other non-conjugated carbonyls in the structure. In order to test this, benzoyl acetone was chosen as a model arene substrate due to the presence of a phenyl ketone and non-conjugated ketone. The ?6 ruthenium—arene complex was successfully synthesized by reacting benzoyl acetone with tris(acetonitrile)cyclopentadienylruthenium(II) hexafluorophosphate, and characterized by 1H NMR. The complex, once purified will be tested for selective reduction of the phenyl ketone moiety as mentioned above. If successful, this research could prove useful in small molecule organic synthesis (e.g. pharmaceuticals) where chemoselective reduction of compounds containing multiple ketone functional groups is often necessary.