A compound of Formula: wherein A 1 is N or CR 1, A 2 is CR 2, A 3 is N or CR 3, and A 4 is CR 4, wherein R 1, R 2, R 3, and R 4 each independently represent hydrogen or halogen, and wherein no more than one of A 1 and A 3 is N; R 5 is hydrogen, C 1-4 alkyl, C 1-2 alkoxyC 1-4 alkyl, C 3-4 alkenyl, C 3-4 alkynyl, cyclopropyl, or cyclopropylmethyl; R 6 is hydrogen, hydroxy, amino, C 1-6 alkyl, C 1-4 alkoxy, C 3-6 alkenyl, C 3-4 alkenyloxy, C 3-6 alkynyl, C 3-4 alkynyloxy, C 1-6 haloalkyl, C 1-4 haloalkoxy, cyanoC 1-6 alkyl, hydroxyC 1-6 alkyl, C 1-2 alkoxyC 1-4 alkyl, di-(C 1-2 alkoxy)C 1-4 alkyl, C 1-2 alkylsulfanylC 1-4 alkyl, N,N-di-C 1-4 alkylamino, aminoC 1-4 alkyl, N-C 1-4 alkylaminoC 1-4 alkyl, N,N-di-C 1-4 alkylaminoC 1-4 alkyl, C 1-4 alkylcarbonylC 1-6 alkyl, C 1-4 alkoxycarbonylC 1-6 alkyl, N-C 1-4 alkylaminocarbonylC 1-4 alkyl, N,N-di-C 1-4 alkylaminocarbonylC 1-4 alkyl, N-C 1-4 alkylcarbonylaminoC 1-4 alkyl, C 1-4 alkylcarbonylaminoC 1-4 alkyl, C 1-4 alkoxycarbonylaminoC 1-4 alkyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-2 alkyl, C 3-8 cycloalkylcarbonylaminoC 1-2 alkyl, phenyl, phenylC 1-2 alkyl, benzyloxy, heteroaryl or heteroarylC 1-2 alkyl, wherein the heteroaryl moiety is a 5- or 6-membered aromatic ring which comprises 1, 2, 3 or 4 heteroatoms individually selected from N, O and S, heterocyclyl or heterocyclylC 1-2 alkyl, wherein the heterocyclyl moiety is a 4- to 6-membered non-aromatic ring which comprises 1, 2 or 3 heteroatoms individually selected from N, O and S, and wherein any cycloalkyl, phenyl, heteroaryl or heterocyclyl moiety is optionally substituted by 1 or 2 substituents, which may be the same or different, selected from R 7; R 7 is selected from methyl, ethyl, iso-propyl, chloro, fluoro, hydroxy, cyano, difluoromethyl, trifluoromethyl, methoxy, ethoxy, difluoromethoxy and cyclopropyl; or when R 6 is C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-2 alkyl, C 3-8 cycloalkylcarbonylaminoC 1-2 alkyl, heterocyclyl, or heterocyclylC 1-2 alkyl, R 7 may represent oxo (=O); or R 5 and R 6, together with the nitrogen atom to which they are attached, form a 4- to 6-membered cycle optionally containing an additional heteroatom or group selected from O, S, S 2, carbonyl (C=O) or NR 8; wherein R 8 is hydrogen, methyl or methoxy; or a salt or an N-oxide thereof. A 1 is N or CR 1, A 2 is CR 2, A 3 is N or CR 3, and A 4 is CR 4, wherein R 1, R 2, R 3, and R 4 each independently represent hydrogen or halogen, and wherein no more than one of A 1 and A 3 is N; R 5 is hydrogen, C 1-4 alkyl, C 1-2 alkoxyC 1-4 alkyl, C 3-4 alkenyl, C 3-4 alkynyl, cyclopropyl, or cyclopropylmethyl; R 6 is hydrogen, hydroxy, amino, C 1-6 alkyl, C 1-4 alkoxy, C 3-6 alkenyl, C 3-4 alkenyloxy, C 3-6 alkynyl, C 3-4 alkynyloxy, C 1-6 haloalkyl, C 1-4 haloalkoxy, cyanoC 1-6 alkyl, hydroxyC 1-6 alkyl, C 1-2 alkoxyC 1-4 alkyl, di-(C 1-2 alkoxy)C 1-4 alkyl, C 1-2 alkylsulfanylC 1-4 alkyl, N,N-di-C 1-4 alkylamino, aminoC 1-4 alkyl, N-C 1-4 alkylaminoC 1-4 alkyl, N,N-di-C 1-4 alkylaminoC 1-4 alkyl, C 1-4 alkylcarbonylC 1-6 alkyl, C 1-4 alkoxycarbonylC 1-6 alkyl, N-C 1-4 alkylaminocarbonylC 1-4 alkyl, N,N-di-C 1-4 alkylaminocarbonylC 1-4 alkyl, N-C 1-4 alkylcarbonylaminoC 1-4 alkyl, C 1-4 alkylcarbonylaminoC 1-4 alkyl, C 1-4 alkoxycarbonylaminoC 1-4 alkyl, C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-2 alkyl, C 3-8 cycloalkylcarbonylaminoC 1-2 alkyl, phenyl, phenylC 1-2 alkyl, benzyloxy, heteroaryl or heteroarylC 1-2 alkyl, wherein the heteroaryl moiety is a 5- or 6-membered aromatic ring which comprises 1, 2, 3 or 4 heteroatoms individually selected from N, O and S, heterocyclyl or heterocyclylC 1-2 alkyl, wherein the heterocyclyl moiety is a 4- to 6-membered non-aromatic ring which comprises 1, 2 or 3 heteroatoms individually selected from N, O and S, and wherein any cycloalkyl, phenyl, heteroaryl or heterocyclyl moiety is optionally substituted by 1 or 2 substituents, which may be the same or different, selected from R 7; R 7 is selected from methyl, ethyl, iso-propyl, chloro, fluoro, hydroxy, cyano, difluoromethyl, trifluoromethyl, methoxy, ethoxy, difluoromethoxy and cyclopropyl; or when R 6 is C 3-8 cycloalkyl, C 3-8 cycloalkylC 1-2 alkyl, C 3-8 cycloalkylcarbonylaminoC 1-2 alkyl, heterocyclyl, or heterocyclylC 1-2 alkyl, R 7 may represent oxo (=O); or R 5 and R 6, together with the nitrogen atom to which they are attached, form a 4- to 6-membered cycle optionally containing an additional heteroatom or group selected from O, S, S 2, carbonyl (C=O) or NR 8; wherein R 8 is hydrogen, methyl or methoxy; or a salt or an N-oxide thereof.