A compound of formula I': wherein: R 4 is: A is phenyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridinyl-2 -one, tetrahydropyrimidin-2 -one, imidazolidinyl-2-one, pyrrolidinyl-2-one, pyrrolidinyl, pyridazinyl, thiazolyl, pyrazin-2 -one, piperazinyl-2-one, piperazinyl, imidazolyl, morpholinyl, 1,2,3,6-tetrahydropyridinyl or piperidinyl, wherein any phenyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridinyl-2 -one, tetrahydropyrimidin-2 -one, imidazolidinyl-2-one, pyrrolidinyl-2-one, pyrrolidinyl, pyridazinyl, thiazolyl, pyrazin-2 -one, piperazinyl-2-one, piperazinyl, imidazolyl, morpholinyl, 1,2,3,6-tetrahydropyridinyl or piperidinyl of A is optionally substituted with one to five Z 1a groups, and B is aryl, heteroaryl or heterocycle, wherein any aryl, heteroaryl or heterocycle of B is optionally substituted with one to five Z 1b groups; or A and B together form a (C 9 -C 14)bicyclic aryl, bicyclic heteroaryl or bicyclic heterocycle, wherein (C 9 -C 14)bicyclic aryl, bicyclic heteroaryl or bicyclic heterocycle is optionally substituted with one to five Z 1b groups; each Z 1a is independently selected from halo, (C 1 -C 3)alkyl, (C 2 -C 3)alkenyl, (C 2 -C 3)alkynyl, (C 1 -C 3)haloalkyl, (C 3 -C 7)carbocycle, heterocycle, -O(C 1 -C 3)alkyl, -O(C 2 -C3)alkenyl, -O(C 2 -C 3)alkynyl, -NR c R d, -NR a C R a, -C OR b and -C NR c R d, wherein any (C 3 -C 7)carbocycle and heterocycle of Z 1a is optionally substituted with one to five halogen or (C 1 -C 6)alkyl; each Z 1b is independently selected from halo, CN, (C 1 -C 6)alkyl, (C 2 -C 6)alkenyl, (C 2 -C 6)alkynyl, (C 1 -C 6)haloalkyl, (C 3 -C 7)carbocycle, heteroaryl, heterocycle, aryl(C 1 -C 6)alkyl-, -OH, -O(C 1 -C 6)alkyl, -O(C 2 -C 6)alkenyl, -O(C 2 -C 6)alkynyl, - NR c R d, -NR a C R a, -C OR b and -C NR c R d, wherein any (C 3 -C 7)carbocycle and heterocycle of Z 1b is optionally substituted with one to five halogen or (C 1 -C 6)alkyl; and R a, Rb, R c and R d are each independently H or (C 1 -C 6)alkyl; wherein each heteroaryl is a single aromatic ring of from 1 to 6 carbon atoms and 1 to 4 heteroatoms selected from the group consisting of oxygen, nitrogen and sulfur or is a portion of a multiple condensed ring system comprising 2 or 3 rings; and wherein each heterocycle is a single saturated or partially unsaturated ring of from 1 to 6 carbon atoms and 1 to 3 heteroatoms selected from the group consisting of oxygen, nitrogen and sulfur or is a portion of a multiple condensed ring system comprising 2 or 3 rings; or a pharmaceutically acceptable salt thereof. R 4 is: A is phenyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridinyl-2 -one, tetrahydropyrimidin-2 -one, imidazolidinyl-2-one, pyrrolidinyl-2-one, pyrrolidinyl, pyridazinyl, thiazolyl, pyrazin-2 -one, piperazinyl-2-one, piperazinyl, imidazolyl, morpholinyl, 1,2,3,6-tetrahydropyridinyl or piperidinyl, wherein any phenyl, pyridinyl, pyrimidinyl, pyrazinyl, pyridinyl-2 -one, tetrahydropyrimidin-2 -one, imidazolidinyl-2-one, pyrrolidinyl-2-one, pyrrolidinyl, pyridazinyl, thiazolyl, pyrazin-2 -one, piperazinyl-2-one, piperazinyl, imidazolyl, morpholinyl, 1,2,3,6-tetrahydropyridinyl or piperidinyl of A is optionally substituted with one to five Z 1a groups, and B is aryl, heteroaryl or heterocycle, wherein any aryl, heteroaryl or heterocycle of B is optionally substituted with one to five Z 1b groups; or A and B together form a (C 9 -C 14)bicyclic aryl, bicyclic heteroaryl or bicyclic heterocycle, wherein (C 9 -C 14)bicyclic aryl, bicyclic heteroaryl or bicyclic heterocycle is optionally substituted with one to five Z 1b groups; each Z 1a is independently selected from halo, (C 1 -C 3)alkyl, (C 2 -C 3)alkenyl, (C 2 -C 3)alkynyl, (C 1 -C 3)haloalkyl, (C 3 -C 7)carbocycle, heterocycle, -O(C 1 -C 3)alkyl, -O(C 2 -C3)alkenyl, -O(C 2 -C 3)alkynyl, -NR c R d, -NR a C R a, -C OR b and -C NR c R d, wherein any (C 3 -C 7)carbocycle and heterocycle of Z 1a is optionally substituted with one to five halogen or (C 1 -C 6)alkyl; each Z 1b is independently selected from halo, CN, (C 1 -C 6)alkyl, (C 2 -C 6)alkenyl, (C 2 -C 6)alkynyl, (C 1 -C 6)haloalkyl, (C 3 -C 7)carbocycle, heteroaryl, heterocycle, aryl(C 1 -C 6)alkyl-, -OH, -O(C 1 -C 6)alkyl, -O(C 2 -C 6)alkenyl, -O(C 2 -C 6)alkynyl, - NR c R d, -NR a C R a, -C OR b and -C NR c R d, wherein any (C 3 -C 7)carbocycle and heterocycle of Z 1b is optionally substituted with one to five halogen or (C 1 -C 6)alkyl; and R a, Rb, R c and R d are each independently H or (C 1 -C 6)alkyl; wherein each heteroaryl is a single aromatic ring of from 1 to 6 carbon atoms and 1 to 4 heteroatoms selected from the group consisting of oxygen, nitrogen and sulfur or is a portion of a multiple condensed ring system comprising 2 or 3 rings; and wherein each heterocycle is a single saturated or partially unsaturated ring of from 1 to 6 carbon atoms and 1 to 3 heteroatoms selected from the group consisting of oxygen, nitrogen and sulfur or is a portion of a multiple condensed ring system comprising 2 or 3 rings;