Application of the Curtius rearrangement to the synthesis of 1′-aminoferrocene-1-carboxylic acid derivatives

The shortest synthesis of N -protected 1′-aminoferrocene-1-carboxylic acid from readily available ferrocene-1,1′-dicarboxylic acid is reported. 1′-Azidocarbonylferrocene-1-carboxylic acid was first obtained by reaction of the latter with diphenylphosphoryl azide. It was then converted into four amino acids by a Curtius rearrangement conducted in the presence of tert -butanol, benzyl alcohol, 9-fluorenemethanol or allyl alcohol. The benzyl and allyl carbamate derivatives are reported and characterized for the first time. The four corresponding new succinimidyl activated esters were also prepared and their usefulness was demonstrated in peptide coupling. Various structures were elucidated by X-ray crystallography, including 1′-azidocarbonylferrocene-1-carboxylic acid and 1,1′-diazidocarbonylferrocene. The shortest synthesis of N -protected 1′-aminoferrocene-1-carboxylic acid from readily available ferrocene-1,1′-dicarboxylic acid is reported.