Abstract: A process for the preparation of 2H-3-isoquinolones having the formula ##SPC1##Wherein R.sub.1 and R.sub.2 are each hydrogen, halogen, lower alkyl, lower alkoxy, aryl, haloaryl, alkylaryl or alkoxyaryl; R.sub.3 and R.sub.4 are each hydrogen, lower alkyl, lower alkoxyalkyl, lower alkenyl, lower alkynyl, cycloalkyl, aryl, aralkyl, or halo-aralkyl, which comprises cyclizing an N-formyl-2-phenyl-acetamide of the formula ##SPC2##Wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 have the same meaning as above, with a cyclodehydration agent. Said 2H-3-isoquinolones are useful as starting materials e.g. in the synthesis of 1,4-dihydro-1,4-etheno-isoquinolin-3(2H)-ones which are valuable chemotherapeutic agents in the treatment of disorders of the central nervous system, such as troubles of wakefulness, disorders of equilibrium and vertigo.