Ferrocene compounds: Part XXXIII. Synthesis and characterization of amino acids containing skeletal 1,1′-ferrocenylene unit

The syntheses of 1′-(3-aminopropyl)ferrocene-1-carboxylic acid (7), 1′-amino-1-ferrocenebutyric acid (14) and their derivatives are reported. Reactions of 1′-methoxycarbonyl-1-ferrocenebutyric acid (3) or methyl 1′-carboxy-1-ferrocenebutyrate (10) with ethyl chloroformate/triethylamine/sodium azide gave methyl 1′-(3-azidocarbonylpropyl)ferrocene-1-carboxylate (4) and methyl 1′-azidocarbonyl-1-ferrocenebutyrate (11). These azides were rearranged by heating in acetic anhydride and hydrolyzed into N-acetyl derivatives of 7 and 14. The crucial intermediates 4 and 11 were transformed by the action of t-BuOH into Boc-7 and Boc-14. The crystal and molecular structures of the intermediates methyl 1′-(3-acetamidopropyl)ferrocene-1-carboxylate (5) and tert-butyl 1′-(3-methoxycarbonylpropyl)-1-ferrocenecarbamate (15) have been determined by the single crystal X-ray analysis. Compound 5 crystallizes in two polymorphic forms (5a and 5b); one of them (5b) contains two crystallographically independent molecules. The molecules 5a and 5b differentiate only in the conformation of (CH2)3NHAc part of the molecules exhibiting conformational polymorphism. The crystal structure is dominated by the intermolecular hydrogens bonds of NH⋯O type (2.820(1)–2.840(2) Å) linking molecules into endless chains in all three structures. The chains are further interconnected by the CH⋯O hydrogen bonds (3.483(1)–3.267(2) Å) in 5a and 15, but not in 5b.The structural features of 5 and 15 determined by the single crystal X-ray analysis, reveal existence of intermolecular hydrogens bonds of NH⋯O type (2.820(1)–2.840(2) Å).