|Abstract||A practical method for the synthesis of an isoquinoline alkaloid 6,7-dimethoxy-2-methylisoquinoline-1,3,4(2H)-trione and its analogues has been demonstrated. Two new methods for synthesizing substituted phthalonimides from the corresponding isocarbostyrils have been developed. Phthalonimide derivatives were obtained by the oxidation of isocarbostyrils protected with methoxymethyl and a,a,a-trichloroethoxymethyl groups. The direct oxidation of isocarbostyrils under different conditions was also investigated. In addition, six dienes for potential use in the development of a [4+2] cycloaddition approach to galanthan tetracyclic ring system have been synthesized. These precursors and dienophiles are based on and drived from isoquinolines and isocarbostyrils.