Compounds having the structural formula I or a pharmaceutically acceptable salt thereof, wherein: X1 and X2 are 1-3 substituents independently selected from the group consisting of H, alkyl, halo, —CF3, —OCF3, alkoxy, —OH and —CN; n is 0, 1 or 2; and R and R1 are H or alkyl; also disclosed is the use of the compounds in the treatment of CNS diseases such as Parkinson's disease, alone or in combination with other agents for treating CNS diseases, pharmaceutical compositions comprising them and kits comprising the components of the combinations.