The present invention relates to compounds of general formula wherein Ar is phenyl or pyridinyl； X1 is N or CH, X2 is N or CH, with the proviso that only one of X1 or X2 is N and the other is CH； R1 is hydrogen, halogen, lower alkyl, lower alkoxy, lower alkyl substituted by halogen, cyano or S(O)2-lower alkyl； R2 is hydrogen, halogen, lower alkyl, lower alkoxy, lower alkyl substituted by halogen or cyano； 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.
