1-Chloro-4-nitro-9,10-dihydroacridin-9-one (I) is refluxed with POCl3 in the presence of a catalytic amount of DMF and subsequently reacted with ammonium carbonate in hot phenol to provide the amino acridine (II). Displacement of the 4-chloro group of (II) with N,N-dimethylethanediamine (III) in DMF at 100 C leads to amine (IV). Cyclization of (IV) with SOCl2 yields the target thiadiazinoacridine, which is finally isolated as the corresponding maleate salt.