The present invention relates to compounds of general formula (I), wherein R1 is hydrogen, halogen, lower alkyl, lower alkoxy, lower alkoxy substituted by halogen or cyano； R2 is hydrogen, lower alkyl or lower alkyl substituted by halogen； R3 is phenyl, benzo[1,3]dioxolyl, 2,3-dihydro-benzofuran-5-yl or a 5- and 6-membered heteroaryl, wherein phenyl and the 5- and 6-membered heteroaryl groups may be substituted by one or more substituents, selected from cyano, nitro, amino and lower di-alkylamino, lower alkyl sulfonyl, lower alkoxy, lower alkoxy substituted by halogen, halogen, lower alkyl, lower alkyl substituted by halogen or lower alkyl substituted by hydroxyl； X is -CH(lower alkyl)-, -CH2-, -CH2CH2- or CH(lower alkyl)CH2-； R is hydrogen or lower alkyl； n is 1 or 2； or to a pharmaceutically acceptable acid addition salt, to a racemic mixture or to its corresponding enantiomer and/or optical isomers thereof. The compounds may be used for the treatment of schizophrenia, obsessive-compulsive personality disorder, major depression, bipolar disorders, anxiety disorders, normal aging, epilepsy, retinal degeneration, traumatic brain injury, spinal cord injury, post-traumatic stress disorder, panic disorder, Parkinson's disease, dementia, Alzheimer's disease, mild cognitive impairment, chemotherapy-induced cognitive dysfunction, Down syndrome, autism spectrum disorders, hearing loss, tinnitus, spinocerebellar ataxia, amyotrophic lateral sclerosis, multiple sclerosis, Huntington's disease, stroke, radiation therapy, chronic stress, abuse of neuro-active drugs, such as alcohol, opiates, methamphetamine, phencyclidine and cocaine.
