An efficient green route for monoacylation of aromatic diamines, namely o-phenylenediamine and p-phenylenediamine and aliphatic diamines ethylenediamine and piperazine using N-acylbenzotriazoles (NABs) in n-butanol was developed. The new protocol does not require prior selective protection of the diamine and comprises simple conditions, short reaction times, an easy work up as well as high isolated yields (69–94%). Moreover, the method described herein enable stepwise acylation of aliphatic diamines such as ethylenediamine and piperazine with two different N-acylbenzotriazoles affording unsymmetrical substituted diamines that can be used for construction of pharmaceutically important targets such as drugs, foldamers, and drug conjugates.