Keywords: Ferrocene / Hydroxybenzotriazole / Amide coupling / Amino acid / Electrochemistry 3-{[1Ј-(tert-Butyloxycarbonylamino)ferrocen-1-yl]carbonyl}-benzotriazole 1-oxide (3) has been successfully separated during the synthesis of benzotriazol-1-yl 1Ј-(tert-butyloxycarbonylamino)ferrocene-1-carboxylate (2) as an active ester for peptide coupling. The yield of 3 increased by using polar, rather than nonpolar solvents. The two compounds have been fully characterized and studied by X-ray crystallography and spectroscopic methods. The active ester derivative 2 formed a urethane bond with the glycine ethyl ester while the N-oxide 3 did not react. The X-ray structural ana-

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