Heterocyclic inhibitors of ATR kinase

A compound of structural Formula (I):

• or a salt thereof, wherein:
• R1 and R2 are independently chosen from C1-4 alkyl, C1-4 haloalkyl, C3-6 cycloalkyl, C3-6 heterocycloalkyl, aryl, and heteroaryl, each of which is optionally substituted with one or more R5 groups, or R1 and R2, together with the sulfur to which they are both attached, form a heterocycloalkyl ring which is optionally substituted with one or more R5 groups;
• R3 is chosen from hydrogen, C1-6 alkyl, and C1-6 haloalkyl;
• R4 is chosen from C5-10 aryl and 5-10 membered heteroaryl, each of which is optionally substituted with one or more R6 groups;
• each R5 is independently chosen from NR8R9, halogen, cyano, hydroxy, oxo, alkyl, haloalkyl, cycloalkyl, heterocycloalkyl, hydroxyalkyl, OR8, NR7C(O)R8, NR7C(O)OR8, NR7C(O)NR8R9, C(O)R8, C(O)OR8, and C(O)NR8R9;
• each R6 is independently chosen from NR11R12, halogen, cyano, hydroxy, oxo, alkyl, haloalkyl, cycloalkyl, heterocycloalkyl, hydroxyalkyl, OR11, NR10C(O)R11, NR10C(O)OR11, NR10C(O)NR11R12, C(O)R11, C(O)OR11, and C(O)NR11R12;
• each R7, R8 and R9 is independently chosen from hydrogen, C1-4 alkyl, C3-6 cycloalkyl, and heterocycloalkyl and is optionally substituted with halo, hydroxy, C1-3 alkyl, C1-3 haloalkyl, and C1-3 alkoxy;
• or any two of R7, R8 and R9, together with the atom to which they are both attached can form a 3-7 membered cycloalkyl or heterocycloalkyl ring;
• and
• each R10, R11 and R12 is independently chosen from hydrogen, C1-4 alkyl, C3-6 cycloalkyl, and heterocycloalkyl and is optionally substituted with one or more groups chosen from halo, hydroxy and alkoxy;
• or any two of R10, R11 and R12, together with the atom to which they are both attached, can form a 3-7 membered cycloalkyl or heterocycloalkyl ring.