HHdeHProvided herein are processes for synthesizing dihydropyridophthalazinone derivatives such as for example 5 fluoro 8 (4 fluorophenyl) 9 (1 methyl 1 1 2 4 triazol 5 yl) 8 9 dihydro 2 pyrido[4 3 2 ]phthalazin 3(7) one and its stereoisomers which are potent poly(ADP ribose)polymerase (PARP) inhibitors as well as novel synthetic intermediate compounds.