The present invention relates to compounds of formula IwhereinR1′ is CH3 R1 is methyl, ethyl, CF3, CH2OH, cyclopropyl or cyano, or R1′ and R1 may form together a 1,1-dioxo-tetrahydro-thiophen-3-yl ringR2 is hydrogen, methyl, ethyl, isopropyl, tert-butyl or cyclopropylR3 is Cl, F, CF3, cyano, methyl, methoxy or cyclopropylR4 is hydrogen, methyl or FX is N or CHY is N or CH with the proviso that X and Y are not simultaneously CHor to a pharmaceutically acceptable salt or acid addition salt, to a racemic mixture, or to its corresponding enantiomer and/or optical isomer and/or stereoisomer thereof.The compounds of formula I may be used in the treatment of psychiatric disorders such as schizophrenia, bipolar disorder, obsessive-compulsive disorder or autism spectrum disorder.
