Piperidinoindole (I) was alkylated with chloroacetonitrile in the presence of Et3N in N-methylpyrrolidinone to afford nitrile (II), which was reduced to primary amine (III) by means of LiAlH4 and AlCl3. A further alkylation-reduction sequence over (III) provided in turn nitrile (IV) and then amine (V). Finally, condensation with phosgene yielded the target imidazolidinone (1).