The procedure of Example 11 is followed but starting with 2-(5-chloro-1,8-naphthyridin-2-yl)-3-phenoxycarbonyloxy-isoindolin-1-one (6.7 g.), 4-methylpiperazine (15.8 g.) and dimethylformamide (32 cc.) and stirring for 15 minutes at 23° C. The reaction mixture is then diluted by adding diisopropyl ether (320 cc.). The precipitate is filtered off, washed with diisopropyl ether (3 × 30 cc.) and then dried. A product (3.8 g.) is obtained which is recrystallised from acetonitrile (300 cc.) to yield 2-(5-chloro-1,8-naphthyridin-2yl)-3-(4-methylpiperazin-1-yl)carbonyloxy-isoindolin-1-one (2.9 g.) melting at 240° C.
