Synthesis of isoquinobenzodiazepinediones

1‐(2′‐Chloroacetylamino)‐4,4‐dimethyl‐1,4‐dihydro‐3(2 H )‐isoquinolinone ( 3 ) was cyclised by treatment with sodium hydride in dimethyl sulphoxide containing 0.1 % of water to give 10,10‐dimethyl‐6,7,9,10‐tetrahydro‐5 H ,14b H ‐isoquino[2,1‐ d ][1,4]benzodiazepine‐6,9‐dione ( 4 ) in a yield of 80%. In anhydrous dimethyl sulphoxide the main product of the reaction was 5‐ N ‐(4,4‐dimethyl‐1‐phenyl‐1,4‐dihydro‐3(2 H )‐isoquinolinon‐1′‐yl)isoquino[2,1‐ d ][1,4]benzodiazepine‐6,9‐dione ( 5 ), which was also prepared by the reaction of 3 with 4 .