Guanidine hydrochloride as an organocatalyst for N-Boc protection of amino groups

A simple and efficient method for the chemoselective N-Boc protection of the amine moiety in a variety of compounds is described using di-tert-butyl dicarbonate and guanidine hydrochloride as an organocatalyst in ethanol at 35–40 °C. Selective mono-N-Boc protection of diamines and chemoselective protection of hydroxylamines without formation of any side products is achieved. Amino acids and peptides are N-Boc protected efficiently in excellent yields under convenient reaction conditions.