A compound of Formula IIa: or a pharmaceutically acceptable salt thereof, wherein: X is carbon or nitrogen; Y is carbon or nitrogen; R 1a is hydrogen, halogen, nitro, cyano, hydroxy, (C 1 -C 6)alkyl, (C 1 -C 6)alkenyl, (C 1 -C 6)alkynyl, (C 1 -C 6)alkoxy, aryl, heteroaryl, cycloalkyl, heterocyclyl, aryl(C 1 -C 3)alkyl, heteroaryl(C 1 -C 3)alkyl, cycloalkyl(C 1 -C 3)alkyl, heterocyclyl(C 1 -C 3)alkyl, hydroxy(C 1 -C 3)alkyl, N(R 5a) 2, C(=NOH)NH 2, NR 5a CON(R 5a) 2, CON(R 5a) 2, CO 2 R 5a, COR 6a, OC R 5a, SO 2 N(R 5a) 2, SO 2 R 6a, NR 5a COR 6a, NR 5a CO 2 R 6a, NR 5a SO 2 R 6a or OC(=O)N(R 5a) 2, each optionally substituted with one or more groups represented by R 4a; R 2a is (C 1 -C 6)alkyl, (C 1 -C 6)alkoxy, S(C 1 -C 6)alkyl, SO(C 1 -C 6)alkyl or SO 2 (C 1 -C 6)alkyl, optionally substituted with one or more groups represented by R 4a; R 3a is halogen, (C 1 -C 6)alkyl or (C 1 -C 6)alkoxy, each optionally substituted with one or more groups represented by R 4a; each R 4a is independently halogen, nitro, cyano, hydroxy, (C 1 -C 4)alkyl, halo(C 1 -C 3)alkyl, hydroxy(C 1 -C 4)alkyl, (C 1 -C 4)alkoxy, halo(C 1 -C 4)alkoxy, aryl, haloaryl, cycloalkyl, aryl(C 1 -C 3)alkyl, aryl(C 1 -C 4)alkoxy, heterocyclyl, N(R 5a) 2, C(=NOH)NH 2, NR 5a CON(R 5a) 2, CON(R 5a) 2, CO 2 R 5a, COR 6a, OC R 5a, SO 2 N(R 5a) 2, SO 2 R 6a, SR 6a, S(C 1 -C 3)alkylcycloalkyl, NR 5a COR 6a, NR 5 CO 2 R 6a, NR 5a SO 2 R 6a, S(=O)R 6a, -O-cycloalkyl, -O-heterocyclyl, adamantyl, OC(=O)N(R 5a) 2, each R 5a is independently hydrogen, (C 1 -C 10)alkyl, aryl or aryl(C 1 -C 6)alkyl, each optionally substituted with halogen, (C 1 -C 3)alkoxy, (C 1 -C 3)alkyl, halo(C 1 -C 3)alkyl, halo(C 1 -C 3)alkoxy, cyano or nitro; and each R 6a is independently hydrogen, halogen, (C 1 -C 10)alkyl, (C 1 -C 10)alkoxy, aryl(C 1 -C 3)alkyl, cycloalkyl or aryl(C 1 -C 3)alkoxy, each optionally substituted with halogen, (C 1 -C 3)alkoxy, (C 1 -C 3)alkyl, halo(C 1 -C 3)alkyl, halo(C 1 -C 3)alkoxy, cyano or nitro. X is carbon or nitrogen; Y is carbon or nitrogen; R 1a is hydrogen, halogen, nitro, cyano, hydroxy, (C 1 -C 6)alkyl, (C 1 -C 6)alkenyl, (C 1 -C 6)alkynyl, (C 1 -C 6)alkoxy, aryl, heteroaryl, cycloalkyl, heterocyclyl, aryl(C 1 -C 3)alkyl, heteroaryl(C 1 -C 3)alkyl, cycloalkyl(C 1 -C 3)alkyl, heterocyclyl(C 1 -C 3)alkyl, hydroxy(C 1 -C 3)alkyl, N(R 5a) 2, C(=NOH)NH 2, NR 5a CON(R 5a) 2, CON(R 5a) 2, CO 2 R 5a, COR 6a, OC R 5a, SO 2 N(R 5a) 2, SO 2 R 6a, NR 5a COR 6a, NR 5a CO 2 R 6a, NR 5a SO 2 R 6a or OC(=O)N(R 5a) 2, each optionally substituted with one or more groups represented by R 4a; R 2a is (C 1 -C 6)alkyl, (C 1 -C 6)alkoxy, S(C 1 -C 6)alkyl, SO(C 1 -C 6)alkyl or SO 2 (C 1 -C 6)alkyl, optionally substituted with one or more groups represented by R 4a; R 3a is halogen, (C 1 -C 6)alkyl or (C 1 -C 6)alkoxy, each optionally substituted with one or more groups represented by R 4a; each R 4a is independently halogen, nitro, cyano, hydroxy, (C 1 -C 4)alkyl, halo(C 1 -C 3)alkyl, hydroxy(C 1 -C 4)alkyl, (C 1 -C 4)alkoxy, halo(C 1 -C 4)alkoxy, aryl, haloaryl, cycloalkyl, aryl(C 1 -C 3)alkyl, aryl(C 1 -C 4)alkoxy, heterocyclyl, N(R 5a) 2, C(=NOH)NH 2, NR 5a CON(R 5a) 2, CON(R 5a) 2, CO 2 R 5a, COR 6a, OC R 5a, SO 2 N(R 5a) 2, SO 2 R 6a, SR 6a, S(C 1 -C 3)alkylcycloalkyl, NR 5a COR 6a, NR 5 CO 2 R 6a, NR 5a SO 2 R 6a, S(=O)R 6a, -O-cycloalkyl, -O-heterocyclyl, adamantyl, OC(=O)N(R 5a) 2, each R 5a is independently hydrogen, (C 1 -C 10)alkyl, aryl or aryl(C 1 -C 6)alkyl, each optionally substituted with halogen, (C 1 -C 3)alkoxy, (C 1 -C 3)alkyl, halo(C 1 -C 3)alkyl, halo(C 1 -C 3)alkoxy, cyano or nitro; and each R 6a is independently hydrogen, halogen, (C 1 -C 10)alkyl, (C 1 -C 10)alkoxy, aryl(C 1 -C 3)alkyl, cycloalkyl or aryl(C 1 -C 3)alkoxy, each optionally substituted with halogen, (C 1 -C 3)alkoxy, (C 1 -C 3)alkyl, halo(C 1 -C 3)alkyl, halo(C 1 -C 3)alkoxy, cyano or nitro.