Potent and selective inhibitors of IRAK4

A compound of Formula (Ia3):

• or a pharmaceutically acceptable salt thereof, wherein:
• R2a is H, C1-4 alkyl, cyclopropyl, cyclobutyl, —CF3, —CHF2, —CH2F, C1-4 alkoxy, halo, or —CN;
• A is C3-10 cycloalkyl or 4- to 10-membered heterocyclyl, wherein the cycloalkyl and heterocyclyl are unsubstituted or substituted with one, two, or three R1;
• RA2 is H;
• C is pyridinyl that is unsubstituted or substituted with one, two, or three R3;
• R1, independently for each occurrence, is C1-8 alkyl, C1-8 haloalkyl, C1-8 alkoxy, halo, C3-8 cycloalkyl, or 3- to 8-membered heterocyclyl;
• R3, independently for each occurrence, is —OH, —CN, halo, —C(X)OR5, —C(X)N(R5)(R6), C1-8 alkyl, C2-8 alkenyl, C1-8 haloalkyl, C1-8 alkoxy, C3-10 cycloalkyl, 4- to 10-membered heterocyclyl, C6-10 aryl, 5- to 10-membered heteroaryl, C1-3 alkyl-(4- to 10-membered heterocyclyl), C1-3 alkyl-(5- to 10-membered heteroaryl), —O—C1-3 alkyl-(4- to 10-membered heterocyclyl), or —O—C1-3 alkyl-(5- to 10-membered heteroaryl) wherein the alkyl, alkenyl, haloalkyl, alkoxy, cycloalkyl, heterocyclyl, aryl, heteroaryl, alkylheterocyclyl, alkylheteroaryl, —O-alkylheterocyclyl, and —O-alkylheteroaryl are unsubstituted or substituted with one, two, or three R4;
• R4, independently for each occurrence, is oxo, —OH, —CN, halo, C1-4 alkyl, C1-4 haloalkyl, C1-4 alkoxy, —C0-3 alkyl-C(X)OR5, —C0-3 alkyl-C(X)N(R5)(R6), or —C0-3 alkyl-(5- to 10-membered heteroaryl), wherein the alkylheteroaryl is unsubstituted or substituted with one, two, or three C1-3 alkyl or halo;
• X is, independently for each occurrence, O or S;
• and
• R5 and R6 are each, independently, hydrogen or C1-4 alkyl;
• provided that when R2a is H, either R1 is not isopropyl or R3 is not