Amination of cyclohexanedione derivative (I) with ammonium acetate in refluxing ethanol affords compound (II), which is converted into tetrahydroquinolinone derivative (IV) by condensation with 3-oxobutylaldehyde dimethylacetal (III) and cyclization by means of KOH in refluxing EtOH. The desired compound is finally obtained by first reaction of ketone (IV) with aminoguanidine hydrochloride (V) in refluxing EtOH/HCl, followed by formation of the corresponding dimethanesulfonate salt by treatment with methanesulfonic acid.