disclosed are compounds of the formula : or pharmaceutically acceptable addition salts thereof wherein : r 1 and r 2 are the same or different and represent hydrogen , halogen , c 1 - c 6 alkyl , c 1 - c 6 alkoxy , c 1 - c 6 alkylthio , hydroxy , amino , mono - or dialkylamino , cyano or trifluoromethyl ; ar represents aryl or heteroaryl , each of which is optionally substituted with r 3 , r 4 and / or r 4 ; r 3 , r 4 , and r 6 independently represent hydrogen , halogen , hydroxy , c 1 - c 6 alkyl , c 1 - c 6 alkoxy , perfluoroalkyl , perfluoroalkoxy , or so 2 nh 2 ; or r 3 and r 4 together with the atoms to which they are attached represent a ring having 5 - 7 atoms ; and r 5 represents hydrogen or c 1 - c 6 alkyl , which compounds are useful for the treatment and / or prevention of neuropsychological disorders including , but not limited to , schizophrenia , mania , dementia , depression , anxiety , compulsive behavior , substance abuse , parkinson - like motor disorders and motion disorders related to the use of neuroleptic agents .