The present invention relates to compounds of general formula Iwherein R1is hydrogen, halogen, lower alkyl, lower alkoxy, lower alkoxy substituted by halogen or cyano； R2is hydrogen, lower alkyl or lower alkyl substituted by halogen； R3is 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-rnembered 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.本發明係關於通式I之化合物其中R1係氫、鹵素、低碳數烷基、低碳數烷氧基、由鹵素取代之低碳數烷氧基或氰基；R2係氫、低碳數烷基或由鹵素取代之低碳數烷基；R3係苯基、苯并[1,3]二氧雜環戊烯基、2,3-二氫-苯并呋喃-5-基或5員及6員雜芳基，其中苯基及5員及6員雜芳基可由一或多個選自以下基團之取代基取代：氰基、硝基、胺基及低碳數二烷基胺基、低碳數烷基磺醯基、低碳數烷氧基、由鹵素取代之低碳數烷氧基、鹵素、低碳數烷基、由鹵素取代之低碳數烷基或由羥基取代之低碳數烷基；X係-CH(低碳數烷基)-、-CH2-、-CH2CH2-或-CH(低碳數烷基)CH2-；R係氫或低碳數烷基；n係1或2；或係關於其醫藥上可接受之酸加成鹽，係關於其外消旋混合物或係
