Deacetylation of chiral ferrocenyl-containing β-diketones promoted by ethylene diamine: Spectroscopic and structural characterization of the fragmentation products

• Ethylenediamine promotes deacetylation of chiral ferrocenyl-containing β-diketones.
• Ketone-containing fragmentation products and 2-methylimidazole are formed.
• Reaction mechanism: intramolecular Michael addition and retro-Mannich rearrangement.
• X-ray crystal structures of a mono- and a binuclear fragmentation product.

It is well known that β-diketones react with primary amines, readily forming the corresponding Schiff base derivatives. However, in the present case, the chiral ferrocenyl-containing β-diketones, 3-(1-ferrocenylethyl)-pentane-2,4-dione (1a), 1-(4-methoxyphenyl)-2-(1-ferrocenylethyl)-butane-1,3-dione (1b), and 1-ferrocenyl-2-(1-ferrocenylethyl)-butane-1,3-dione (1c) react with ethylene diamine under acidic conditions in refluxing toluene to yield, unexpectedly, their deacetylated counterparts, 3-ferrocenyl-butane-2-one (2a), 1-(4-methoxyphenyl)-3-ferrocenyl-butane-1-one (2b), and 1,3-bisferrocenyl-butane-2-one (2c), respectively. Such deacetylation reactions are accompagned by the formation of 2-methyl-2-imidazoline. A reaction mechanism involving an intramolecular Michael addition followed by a retro-Mannich rearrangement is suggested. The ketones 2a–c are fully characterized by analytical and spectroscopic methods. Additionally, compounds 2a and 2c are authenticated by single crystal X-ray diffraction analysis. The electrochemical behaviour of the bimetallic complex 2c is also investigated.

Chiral ferrocenyl-containing β-diketones were deacetylated in presence of ethylenediamine under acidic conditions in refluxing toluene, leading to the formation of ketone-containing fragmentation products and 2-methyl-4,5-dihydro-1-H-imidazole via an intramolecular Michael addition and retro-Mannich rearrangement sequence; a mono- and a binuclear fragmentation compound were structurally characterized.Figure optionsDownload as PowerPoint slide