The present invention relates to compounds of formula I wherein L is a bond, a triple bond, —C(O)NH— or —NHC(O)—; R1 is phenyl or a five or six-membered heteroaryl group, optionally substituted by lower alkyl, lower alkyl substituted by halogen or lower alkoxy substituted by halogen; R2 is fluoro; R3 is fluoro or chloro; R4 is hydrogen, lower alkyl, halogen, lower alkyl substituted by hydroxy, S(O)2CH3, or is a five or six-membered heteroaryl group or a heterocycloalkyl group, which are optionally substituted by lower alkyl, hydroxy or ═O; R5 and R6 are both methyl and the dotted line is a bond, or R5 and R6 are both methyl and the dotted line is nothing, or one of R5 and R6 is hydrogen and the other is methyl, and the dotted line is nothing; or to a pharmaceutically acceptable salt or acid addition salt, to all possible tautomeric forms, to a racemic mixture, or to its corresponding enantiomer and/or optical isomer and/or stereoisomer thereof. The compounds may be used for the treatment of Parkinson's disease, anxiety, emesis, obsessive compulsive disorder, autism, neuroprotection, cancer, depression and diabetes type 2.