The present invention relates to a process for the preparation of Cyclen, in its turn widely employed in the manufacturing of a variety of macrocyclic gadolinium complexes for use as MRI contrast agents. The said process comprises an efficient coupling of glyoxal with triethylene tetramine and the subsequent reduction of the obtained intermediate derivative with an aluminium based reducing agent. The process is particularly advantageous for the industrial scale as it avoids the use and/or formation of hazardous compounds and further provides for Cyclen manufacturing in high yields and purity.
