A compound of structural Formula (I): or a salt thereof, wherein: R 1 and R 2 are independently chosen from C 1-4 alkyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C3-6 heterocycloalkyl, aryl, and heteroaryl, each of which is optionally substituted with one or more R 5 groups, or R 1 and R 2 , together with the sulfur to which they are both attached, form a heterocycloalkyl ring which is optionally substituted with one or more R 5 groups; R 3 is chosen from hydrogen, C 1-6 alkyl, and C 1-6 haloalkyl; R 4 is chosen from C 5-10 aryl and 5-10 membered heteroaryl, each of which is optionally substituted with one or more R 6 groups; each R 5 is independently chosen from NR 8 R 9 , halogen, cyano, hydroxy, oxo, alkyl, haloalkyl, cycloalkyl, heterocycloalkyl, hydroxyalkyl, OR 8 , NR 7 C(O)R 8 , NR 7 C(O)OR 8 , NR 7 C(O)NR 8 R 9 , C(O)R 8 , C(O)OR 8 , and C(O)NR 8 R 9 ; each R 6 is independently chosen from NR 11 R 12 , halogen, cyano, hydroxy, oxo, alkyl, haloalkyl, cycloalkyl, heterocycloalkyl, hydroxyalkyl, OR 11 , NR 10 C(O)R 11 , NR 10 C(O)OR 11 , NR 10 C(O)NR 11 R 12 , C(O)R 11 , C(O)OR 11 , and C(O)NR 11 R 12 ; each R 7 , R 8 and R 9 is independently chosen from hydrogen, C 1-4 alkyl, C 3-6 cycloalkyl, and heterocycloalkyl and is optionally substituted with halo, hydroxy, C 1-3 alkyl, C 1-3 haloalkyl, and C 1-3 alkoxy; or any two of R 7 , R 8 and R 9 , together with the atom to which they are both attached can form a 3-7 membered cycloalkyl or heterocycloalkyl ring; and each R 10 , R 11 and R 12 is independently chosen from hydrogen, C 1-4 alkyl, C 3-6 cycloalkyl, and heterocycloalkyl and is optionally substituted with one or more groups chosen from halo, hydroxy and alkoxy; or any two of R 10 , R 11 and R 12 , together with the atom to which they are both attached, can form a 3-7 membered cycloalkyl or heterocycloalkyl ring. R 1 and R 2 are independently chosen from C 1-4 alkyl, C 1-4 haloalkyl, C 3-6 cycloalkyl, C3-6 heterocycloalkyl, aryl, and heteroaryl, each of which is optionally substituted with one or more R 5 groups, or R 1 and R 2 , together with the sulfur to which they are both attached, form a heterocycloalkyl ring which is optionally substituted with one or more R 5 groups; R 3 is chosen from hydrogen, C 1-6 alkyl, and C 1-6 haloalkyl; R 4 is chosen from C 5-10 aryl and 5-10 membered heteroaryl, each of which is optionally substituted with one or more R 6 groups; each R 5 is independently chosen from NR 8 R 9 , halogen, cyano, hydroxy, oxo, alkyl, haloalkyl, cycloalkyl, heterocycloalkyl, hydroxyalkyl, OR 8 , NR 7 C(O)R 8 , NR 7 C(O)OR 8 , NR 7 C(O)NR 8 R 9 , C(O)R 8 , C(O)OR 8 , and C(O)NR 8 R 9 ; each R 6 is independently chosen from NR 11 R 12 , halogen, cyano, hydroxy, oxo, alkyl, haloalkyl, cycloalkyl, heterocycloalkyl, hydroxyalkyl, OR 11 , NR 10 C(O)R 11 , NR 10 C(O)OR 11 , NR 10 C(O)NR 11 R 12 , C(O)R 11 , C(O)OR 11 , and C(O)NR 11 R 12 ; each R 7 , R 8 and R 9 is independently chosen from hydrogen, C 1-4 alkyl, C 3-6 cycloalkyl, and heterocycloalkyl and is optionally substituted with halo, hydroxy, C 1-3 alkyl, C 1-3 haloalkyl, and C 1-3 alkoxy; or any two of R 7 , R 8 and R 9 , together with the atom to which they are both attached can form a 3-7 membered cycloalkyl or heterocycloalkyl ring; and each R 10 , R 11 and R 12 is independently chosen from hydrogen, C 1-4 alkyl, C 3-6 cycloalkyl, and heterocycloalkyl and is optionally substituted with one or more groups chosen from halo, hydroxy and alkoxy; or any two of R 10 , R 11 and R 12 , together with the atom to which they are both attached, can form a 3-7 membered cycloalkyl or heterocycloalkyl ring. <EOS>