A compound of formula wherein R 1 is phenyl substituted by one or two substituents independently selected from C 1-6 alkyl, -OR 5, halo -CN, -COR 6, CO 2 R 7, -CONR 8 R 9, -NR 10 R 11, -NHCOR 12, -SO 2 R 13,-(CH 2) m SO 2 NR 14 R 15, -NHSO 2 R 16, and 5-membered heteroaryl wherein the 5-membered heteroaryl contains one or two heteroatoms independently selected from oxygen and nitrogen; or pyridinyl optionally substituted by one or two substituents independently selected from C 1-6 alkyl, -OR 17, halo, -SO 2 R 18, -SO 2 NR 19 R 20, -NHSO 2 R 21 and -NHCOR 24; R 2 is -(CH 2) n -phenyl optionally substituted by -CN or -NR 22 R 23; 5- or 6-membered heteroaryl wherein the 5- or 6-membered heteroaryl contains one or two heteroatoms independently selected from oxygen, nitrogen and sulphur and is optionally substituted by C 1-6 alkyl, halo or -(CH 2) q NR 25 R 26; or C 3-6 cycloalkyl optionally substituted by phenyl; R 3 is hydrogen or fluoro; R 4 is hydrogen or methyl; R 7, R 17, R 19, R 20, R 22, R 23, R 27, R 28 and R 29 are each independently hydrogen or C 1-6 alkyl; R 5 is hydrogen, C 1-6 alkyl or -CF 3; R 6, R 12, R 13, R 18, R 33 and R 34 are each independently C 1-6 alkyl; R 8 and R 9 are each independently hydrogen or C 1-6 alkyl, or R 8 and R 9, together with the nitrogen atom to which they are attached, are linked to form a 5- or 6-membered heterocyclyl optionally containing an oxygen atom; R 10 and R 11 are each independently hydrogen or C 1-6 alkyl, or R 10 and R 11, together with the nitrogen atom to which they are attached, are linked to form a 5- or 6-membered heterocyclyl optionally containing an oxygen atom; R 14 and R 15 are each independently hydrogen, C 1-6 alkyl, C 3-6 cycloalkyl or -(CH 2) p phenyl, or R 14 and R 15, together with the nitrogen atom to which they are attached, are linked to form a 5- or 6-membered heterocyclyl optionally containing an oxygen atom; R 16 is C 1-6 alkyl; or phenyl optionally substituted by C 1-6 alkyl; R 21 is C 3-6 cycloalkyl; C 1-6 alkyl optionally substituted by -CF 3; phenyl optionally substituted by one or two substituents independently selected from C 1-6 alkyl, -OR 27, -CO 2 R 28 and halo; -(CH 2) u NR 35 R 36; or 5-membered heteroaryl wherein the 5-memebered heteroaryl contains one or two heteroatoms independently selected from oxygen, nitrogen and sulphur and is optionally substituted by one or two substituents independently selected from C 1-6 alkyl; R 24 is C 1-6 alkyl optionally substituted by -OR 29; R 25 and R 26, together with the nitrogen atom to which they are attached, are linked to form a 5-, 6- or 7-membered heterocyclyl or a 10-membered bicyclic heterocyclyl wherein the 5-, 6- or 7-membered heterocyclyl or the 10-membered bicyclic heterocyclyl optionally contains an oxygen atom, a sulphur atom or a further nitrogen atom and is optionally substituted by one or two substituents independently selected from C 1-6 alkyl, C 3-6 cycloalkyl, halo, oxo, phenyl optionally substituted by halo, pyridinyl, -(CH 2) r OR 30, - (CH 2) s NR 31 R 32, -COR 33 and -SO 2 R 34; R 30 is hydrogen, C 1-6 alkyl or -(CH 2) t phenyl; R 31 and R 32, together with the nitrogen atom to which they are attached, are linked to form a 6-membered heterocyclyl optionally containing an oxygen atom; R 35 and R 36, together with the nitrogen atom to which they are attached, are linked to form a 5- or 6-membered heterocyclyl wherein the 5- or 6-membered heterocyclyl optionally contains an oxygen atom or a further nitrogen atom and is optionally substituted by one or two substituents independently selected from C 1-6 alkyl; m, n, p, q, r, s and t are each independently 0, 1 or 2; and u is 1 or 2; or a salt thereof.