Compounds of formula (I) or a salt thereof are disclosed: wherein R1 is pyrazolyl substituted by two or three substituents independently selected from halogen, C1-4alkyl and haloC1-4alkyl； R2 is hydrogen or methyl； and R3 is quinolinyl, oxazolyl or phenyl, each of which is optionally substituted by one or two halogen, C1-4alkyl or haloC1-4alkyl. Processes for preparation and uses of the compounds in medicine, for example for the treatment of schizophrenia or drug dependency, are also disclosed.
