1,4-Dihydro-1-phenyl-3(2H)-isoquinolinone is used as a reagent in the synthesis of a series of 1-aryl-3-dimethylamino-1,4-dihydroisoquinolines which display anti-arthritic activity. Also used as a reagent in the synthesis of 1-aryl-1,4-dihydro-3(2H)-isoquinolinones which have potential antiserotoninergic activity.