the present invention is directed to compounds of formula , and the pharmaceutically acceptable acid addition salts thereof , wherein r is selected from the group consisting of f ,-- cf 3 , -- och 3 , -- oalkyl substituted with 1 to 3 fluoro atoms . -- o substituted with 1 to 5 fluoro atoms , and -- oalkyl substituted with 1 to 7 fluoro atoms . the compounds of formula are useful in the treatment of stroke , traumatic brain injury and central nervous system degenerative diseases .