The invention relates to novel [(5,6-dichloro-3-oxo-2,3,9,9a-tetrahydrofluoren-7-yl)]alkanoic acids and alkanimidamides bearing novel functional 9a-substituents, their derivatives and their salts. The compounds are useful for the treatment and prevention of injury to the brain and of edema due to head trauma, stroke (particularly ischemic), arrested breathing, cardiac arrest, Reye's syndrome, cerebral thrombosis, cerebral embolism, the neurological problems caused by AIDS, cerebral hemorrhage, cerebral tumors, encephalomyelitis, spinal cord injury, hydrocephalus, post-operative brain injury trauma, edema due to cerebral infections, various brain concussions and elevated intracranial pressure.