The reaction of methyl anthranilate (I) with tetrahydrofuran-2,4-dione (II) by means of HCl in ethanol gives 2-(5-oxo-2,5-dihydrofuran-3-ylamino)benzoic acid methyl ester (III), which is cyclized by means of polyphosphoric acid (PPA) at 130-140 C yielding the tricyclic hydroxyketone (IV). The condensation of (IV) with 4-(2-aminoethyl)-1-benzylpiperidine (V) in N-methyl-2-pyrrolidone by a Dean-Stark elimination of water affords 2-[2-(1-benzyl-piperidin-4-yl)ethyl]-9-hydroxy-2,3-dihydro-1H-pyrrolo[3,4-b]quinolin-1-one (VI), which is finally methylated with diazomethane in methanol.