One-Pot Synthesis of 1,1‘-Bis(2-amino)ethyl-Substituted Ferrocenes from the Reaction of Spiro[2.4]hepta-4,6-diene with Lithium Amides: An Expedient Route into Functionalized Ferrocenophanes

The reaction of lithium amides with spiro[2.4]hepta-4,6-diene 2 affords the corresponding (2-aminoethyl)CpLi cyclopropane-ring-opened product that can be trapped in situ with FeCl2 to provide a direct route into 1,1‘-bis-aminoethyl ferrocenes 3. In addition to the desired bis-amine products, a number of interesting ferrocene byproducts have been identified. Their formation can be attributed to the associated Brønsted basicity of the lithium amide nucleophiles and their ability to participate in SET processes, opening-up alternative reaction pathways. The desired aminoethyl-substituted ferrocene products are derived primarily from direct nucleophilic cyclopropane ring-opening rather than via amidolithiation of vinylCp intermediates.