A process for the preparation of compounds of Formula I comprising step a) wherein i) a compound of Formula II is reacted with an acid or base and ii) a compound of Formula I is isolated from the reaction mixture, wherein - R 1 is selected from the group consisting of H, F, Cl, Br and I; - R 2 is selected from the group consisting of C 1-5 alkyl and C 3-5 cycloalkyl - R 3 is selected from the group consisting of deuterium, F, Cl, Br and I; - R 4 is selected from the group consisting of H, deuterium, C 1-5 alkyl, C 2-5 alkenyl, C 2-5 alkynyl, C 3-5 cycloalkyl and C 5 cycloalkenyl, each of which may be optionally substituted with one or more, identical or different, substituents R 7; - R 5 is selected from the group consisting of C 1-5 alkyl optionally substituted with one or more, identical or different, substituents R 8, C 2-5 alkenyl, C 2-5 alkynyl, C 3-6 cycloalkyl optionally substituted with one or more, identical or different, substituents R 8, phenyl optionally substituted with one or more, identical or different, substituents R 9 and benzyl optionally substituted with one or more, identical or different, substituents R 9; - R 6 is selected from the group consisting of H, deuterium C 1-5 alkyl and C 3-5 cycloalkyl; - R 7 is independently selected from the group consisting of deuterium, tritium, F, Cl, Br, I, CN, isocyanide, C 3-5 cycloalkyl optionally substituted with one or more, identical or different, substituents R 8, O-C 1-3 alkyl optionally substituted with one or more, identical or different, substituents R 8, S-C 1-3 alkyl optionally substituted with one or more, identical or different, substituents R 8, CH 2 -O-C 1-3 alkyl optionally substituted with one or more, identical or different, substituents R 8 and CH 2 -S-C 1-3 alkyl optionally substituted with one or more, identical or different, substituents R 8; - R 8 is independently selected from the group consisting of deuterium and F; - R 9 is independently selected from the group consisting of deuterium, methoxy, nitro, cyano, Cl, Br, I and F; and - n is an integer 0, 1, 2 or 3. i) a compound of Formula II is reacted with an acid or base and ii) a compound of Formula I is isolated from the reaction mixture, - R 1 is selected from the group consisting of H, F, Cl, Br and I; - R 2 is selected from the group consisting of C 1-5 alkyl and C 3-5 cycloalkyl - R 3 is selected from the group consisting of deuterium, F, Cl, Br and I; - R 4 is selected from the group consisting of H, deuterium, C 1-5 alkyl, C 2-5 alkenyl, C 2-5 alkynyl, C 3-5 cycloalkyl and C 5 cycloalkenyl, each of which may be optionally substituted with one or more, identical or different, substituents R 7; - R 5 is selected from the group consisting of C 1-5 alkyl optionally substituted with one or more, identical or different, substituents R 8, C 2-5 alkenyl, C 2-5 alkynyl, C 3-6 cycloalkyl optionally substituted with one or more, identical or different, substituents R 8, phenyl optionally substituted with one or more, identical or different, substituents R 9 and benzyl optionally substituted with one or more, identical or different, substituents R 9; - R 6 is selected from the group consisting of H, deuterium C 1-5 alkyl and C 3-5 cycloalkyl; - R 7 is independently selected from the group consisting of deuterium, tritium, F, Cl, Br, I, CN, isocyanide, C 3-5 cycloalkyl optionally substituted with one or more, identical or different, substituents R 8, O-C 1-3 alkyl optionally substituted with one or more, identical or different, substituents R 8, S-C 1-3 alkyl optionally substituted with one or more, identical or different, substituents R 8, CH 2 -O-C 1-3 alkyl optionally substituted with one or more, identical or different, substituents R 8 and CH 2 -S-C 1-3 alkyl optionally substituted with one or more, identical or different, substituents R 8; - R 8 is independently selected from the group consisting of deuterium and F; - R 9 is independently selected from the group consisting of deuterium, methoxy, nitro, cyano, Cl, Br, I and F; and - n is an integer 0, 1, 2 or 3.