the novel compound , 3 -- 3 , 4 - dihydrophthalazin - 1 - one and novel 3 -- 3 , 4 - dihydro - phthalazin - 1 - ones , such as 3 -- 3 , 4 - dihydro - phthalazin - 1 - one and 3 -- 3 , 4 - dihydro - phthalazin - 1 - one ; useful as immunomodulators ; and processes for the synthesis of the compounds .