A compound of formula I, wherein R 1 is halogen, and R 2 is selected from the group consisting of i) heteroaryl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; ii) aryl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; iii) C 3-7 -cycloalkyl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; and iv) C 1-6 -alkyl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 3-7 -cycloalkyl, C 1-6 -alkoxy and halogen-C 1-6 -alkoxy; or pharmaceutically acceptable salts thereof. R 1 is halogen, and R 2 is selected from the group consisting of i) heteroaryl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; ii) aryl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; iii) C 3-7 -cycloalkyl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; and iv) C 1-6 -alkyl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 3-7 -cycloalkyl, C 1-6 -alkoxy and halogen-C 1-6 -alkoxy; i) heteroaryl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; ii) aryl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; iii) C 3-7 -cycloalkyl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 1-6 -alkyl, C 1-6 -alkoxy, halogen-C 1-6 -alkyl, halogen-C 1-6 -alkoxy, C 1-6 -alkoxy-C 1-6 -alkyl and hydroxy-C 1-6 -alkyl; and iv) C 1-6 -alkyl, unsubstituted or substituted by 1 to 3 substituents individually selected from the group consisting of OH, halogen, cyano, C 3-7 -cycloalkyl, C 1-6 -alkoxy and halogen-C 1-6 -alkoxy;