A compound of formula (I') in free form or in pharmaceutically acceptable salt form wherein: a) R 1 is a five- to six-membered monocyclic saturated or unsaturated non-aromatic ring system, wherein said ring system may contain from 1 to 4 hetero atoms selected from nitrogen, oxygen and sulfur, and wherein said ring system may be substituted once or more than once by R 6, wherein each R 6 independently is halogen, hydroxyl, amino, cyano, nitro, C 1-4 alkyl, C 1-4 halogenalkyl, C 1-4 alkoxy or C 3-6 cycloalkyl; and R 2 is C 2-6 alkyl, cyclopropyl, cyclobutyl or cyclopentyl; or b) R 1 is wherein the phenyl ring is attached via the bond marked with an asterisk; each R 12 is hydrogen; and R 2 is C 2-7 alkyl, cyclopropyl, cyclobutyl or cyclopentyl; or c) R 1 is a ring selected from pyrrolyl and pyridin-2-yl, which ring may be substituted by C 1-3 alkyl; and R 2 is C 2-7 alkyl, cyclopropyl, cyclobutyl or cyclopentyl; R 3 is hydrogen or -CH 2 R 18 and R 18 is hydrogen; R 4 and R 5 are independently selected from hydrogen and C 1- C 3 alkyl; or R 4 and R 5 together with the bond to which they are attached form a ring, which is selected from - 5- to 7-membered monocyclic non-aromatic carbocyclic ring, which may be substituted once or more than once by R 19; - a thiophene ring, which may be substituted once by R 20; and - which is fused to the rest of the molecule by the bond marked with two asterisks; R 19 and R 20 are independently selected from halogen and C 1- C 3 alkyl; R 21 is hydrogen, or R 3 and R 21 taken together are -CH 2 -CH 2 -; R 22 is hydrogen; and R 24 is hydrogen or halogen. a) R 1 is a five- to six-membered monocyclic saturated or unsaturated non-aromatic ring system, wherein said ring system may contain from 1 to 4 hetero atoms selected from nitrogen, oxygen and sulfur, and wherein said ring system may be substituted once or more than once by R 6, wherein each R 6 independently is halogen, hydroxyl, amino, cyano, nitro, C 1-4 alkyl, C 1-4 halogenalkyl, C 1-4 alkoxy or C 3-6 cycloalkyl; and R 2 is C 2-6 alkyl, cyclopropyl, cyclobutyl or cyclopentyl; or b) R 1 is wherein the phenyl ring is attached via the bond marked with an asterisk; each R 12 is hydrogen; and R 2 is C 2-7 alkyl, cyclopropyl, cyclobutyl or cyclopentyl; or wherein the phenyl ring is attached via the bond marked with an asterisk; each R 12 is hydrogen; and R 2 is C 2-7 alkyl, cyclopropyl, cyclobutyl or cyclopentyl; c) R 1 is a ring selected from pyrrolyl and pyridin-2-yl, which ring may be substituted by C 1-3 alkyl; and R 2 is C 2-7 alkyl, cyclopropyl, cyclobutyl or cyclopentyl; R 3 is hydrogen or -CH 2 R 18 and R 18 is hydrogen; R 4 and R 5 are independently selected from hydrogen and C 1- C 3 alkyl; or R 4 and R 5 together with the bond to which they are attached form a ring, which is selected from - 5- to 7-membered monocyclic non-aromatic carbocyclic ring, which may be substituted once or more than once by R 19; - a thiophene ring, which may be substituted once by R 20; and - which is fused to the rest of the molecule by the bond marked with two asterisks; R 19 and R 20 are independently selected from halogen and C 1- C 3 alkyl; R 21 is hydrogen, or R 3 and R 21 taken together are -CH 2 -CH 2 -; R 22 is hydrogen; and R 24 is hydrogen or halogen. - 5- to 7-membered monocyclic non-aromatic carbocyclic ring, which may be substituted once or more than once by R 19; - a thiophene ring, which may be substituted once by R 20; and - which is fused to the rest of the molecule by the bond marked with two asterisks;