Stereoselective synthesis and redox properties of ferrocene-substituted pyrrolidines via [3+2] cycloaddition

Abstract

A new series of ferrocene-containing pyrrolidine derivatives was synthesized through a [3+2] dipolar cycloaddition of azomethine ylides with 1-ferrocenyl-2-nitroethene. Under mild conditions and in the presence of silver acetate and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), the reaction was performed repeatedly to afford six novel compounds in moderate to good yields. Structural elucidation was achieved by NMR and IR, while single-crystal X-ray diffraction of two representative compounds unambiguously confirmed the stereochemical outcome and spatial orientation of the substituents. The stereochemical preferences were rationalized by charge distribution, steric effects of the bulky ferrocene group, and secondary orbital interactions, consistent with an endo reaction pathway. According to X-ray analysis, all five substituents of the pyrrolidine ring are involved in intermolecular interactions, while a double chain composed solely of ferrocenyl units appears as the most prominent structural feature. The non-covalent interactions were analyzed based on interaction energy. Electrochemical properties were examined by cyclic voltammetry (CV), which revealed a reversible one-electron redox process. The anodic peak potentials were shifted relative to ferrocene, reflecting the influence of electron-withdrawing nitro substituents. These findings highlight the dual synthetic and biological relevance of ferrocenyl pyrrolidines as redox-active scaffolds with antioxidant potential.