A compound of formula I-a or a pharmaceutically acceptable salt thereof, wherein Q is 2,6-pyrimidyl； in which Q is optionally substituted with 1-5 occurrences of JQ； R1 is - (C1-2 aliphatic) p-R4, in which each R1 is optionally substituted with 1-3 occurrences of J； R2 is - (C1-2 aliphatic) d-R5, in which R1 is optionally substituted with 1-3 occurrences of J； R3 is halogen, -CN, -NO2 or - (U) mX, in which U is a C1-6 aliphatic, in which up to two methylene units are optionally replaced by GU and in which U is optionally substituted with 1 -4 JU； X is H, halogen, CN, NO2, S (O) R, SO2R, C1-4 haloaliphatic or a group selected from C1-6 aliphatic, a C3-10 cycloaliphatic, C6-10 aryl, 5-10 membered heteroaryl, 5-10 membered heterocyclyl； wherein said group is optionally substituted with 1-4 JX； GU is -NH-, -NR-, -O-, -S-, -CO2-, -OC (O) -, -C (O) CO-, -C (O) -, -C (O) NH -, - C (O) NR-, -C (= N-CN) -, -NHCO-, -NRCO-, -NHC (O) O-, -NRC (O) O -, - SO2NH-, -SO2NR -, -NHSO2-, -NRSO2-, - NHC (O) NH-, -NRC (O) NH-, -NHC (O) NR-, -NRC (O) NR, -OC (O) NH-, - OC (O) NR-, -NHSO2NH-, -NRSO2NH-, - NHSO2NR-, -NRSO2NR-, -SO- or -SO2-； R4 is H, halogen, CN, NH2, NO2, CF3, C1-3 aliphatic, cyclopropyl, NCH3, OCH3, -C (= O) NH2, -C (= O) CH3, - NC (= O) CH3 or OH ； R5 is H, halogen, CN, NH2, NO2, CF3, C1-3 aliphatic, cyclopropyl, NCH3, OCH3, -C (= O) NH2, -C (= O) CH3, - NC (= O) CH3 or OH ； JQ is halogen, OCF3, - (Vn) -R ", - (Vn) -CN, - (Vn) -NO2 or- (Vn) - (C1-4 haloaliphatic), in which JQ 20 is not H； V it is a C1-10 aliphatic, in which up to three methylene units are replaced by GV, in which GV is selected from -NH-, -NR-, -O-, -S-, -CO2-, -OC ( O) -, -C (O) CO-, -C (O) -, -C (O) NH-, -C (O) NR-, -C (= N-CN), - NHCO-, -NRCO -, -NHC (O) O-, -NRC (O) O -, - SO2NH-, -SO2NR-, -NHSO2-, -NRSO2-, -NHC (O) NH-, -NRC (O) NH-, - NHC (O) NR-, -NRC (O) NR, -OC (O) NH-, -OC (O) NR-, -NHSO2NH-, -NRSO2NH-, -NHSO2NR-, -NRSO2NR-, -SO- , or-SO2-； and in which V is optionally substituted with 1-6 occu
