HECNU can be prepared as follows (2): The reaction of 2-chloroethylisocyanate (I) with activated sodium azide yields 2-chloroethylcarbamoylazide (II). The preparation of N-(2-chloroethyl)-N-nitrosocarbamoylazide (III) was performed by adding 2-chloroethylcarbamoyiazide (III) to a suspension of anhydrous sodium acetate and nitrogen tetroxide in carbon tetrachloride. Reaction of N-(2-chloroethyl)-N-nitrosocarbamoylazide (III) with ethanolamine (IV) in isopropanol yields elmustine. The described synthetic approach offers a useful means to get the nitroso group attached to the required position.