A compound of formula (IIIa-3), a stereoisomer or pharmaceutically acceptable salt thereof: wherein, R 3 and R 4, together with the nitrogen atom directly attached thereto, form a 5-6 membered heterocyclyl, above groups are further optionally substituted by one or more substituents selected from the group consisting of deuterium, fluorine, methyl, ethyl, isopropyl, cyclopropyl, oxa-cyclobutyl, =O, hydroxy, methoxy, ethoxy, amino and dimethylamino; R 5 is selected from the group consisting of deuterium, C 1-4 alkyl, C 3-8 cycloalkyl and 3-8 membered heterocyclyl, above groups are further optionally substituted by one or more substituents selected from the group consisting of deuterium, halogen, cyano, C 1-4 alkyl, C 3-6 cycloalkyl, 3-6 membered heterocyclyl and C 1-4 alkoxy; R 12 a is hydrogen or deuterium, R 13 a is selected from ( i) C 1-8 alkyl, said C 1-8 alkyl is further substituted by one or more substituents selected from the group consisting of C 3-8 cycloalkyl, C 3-8 cycloalkyloxy, 3-8 membered heterocyclyl, and 3-8 membered heterocyclyloxy, said C 3-8 cycloalkyl, or 3-8 membered heterocyclyl is optionally further substituted by one or more substituents selected from the group consisting of deuterium, halogen, C 3-8 cycloalkyl, 3-8 membered heterocyclyl, hydroxy and C 1-4 alkoxy, or, (ii) C 3-10 cycloalkyl or 3-10 membered heterocyclyl, said C 3-10 cycloalkyl, or 3-10 membered heterocyclyl is optionally further substituted by one or more substituents selected from the group consisting of deuterium, halogen, hydroxy, C 1-4 alkyl, C 1-4 alkoxy, C 3-8 cycloalkyl, C 3-8 cycloalkyloxy, 3-8 membered heterocyclyl, and 3-8 membered heterocyclyloxy, said C 1-4 alkyl, C 3-8 cycloalkyl, or 3-8 membered heterocyclyl is optionally further more substituted by one or more substituents selected from the group consisting of deuterium, halogen, C 3-8 cycloalkyl, 3-8 membered heterocyclyl, hydroxy and C 1-4 alkoxy. R 3 and R 4, together with the nitrogen atom directly attached thereto, form a 5-6 membered heterocyclyl, above groups are further optionally substituted by one or more substituents selected from the group consisting of deuterium, fluorine, methyl, ethyl, isopropyl, cyclopropyl, oxa-cyclobutyl, =O, hydroxy, methoxy, ethoxy, amino and dimethylamino; R 5 is selected from the group consisting of deuterium, C 1-4 alkyl, C 3-8 cycloalkyl and 3-8 membered heterocyclyl, above groups are further optionally substituted by one or more substituents selected from the group consisting of deuterium, halogen, cyano, C 1-4 alkyl, C 3-6 cycloalkyl, 3-6 membered heterocyclyl and C 1-4 alkoxy; R 12 a is hydrogen or deuterium, R 13 a is selected from ( i) C 1-8 alkyl, said C 1-8 alkyl is further substituted by one or more substituents selected from the group consisting of C 3-8 cycloalkyl, C 3-8 cycloalkyloxy, 3-8 membered heterocyclyl, and 3-8 membered heterocyclyloxy, said C 3-8 cycloalkyl, or 3-8 membered heterocyclyl is optionally further substituted by one or more substituents selected from the group consisting of deuterium, halogen, C 3-8 cycloalkyl, 3-8 membered heterocyclyl, hydroxy and C 1-4 alkoxy, or, (ii) C 3-10 cycloalkyl or 3-10 membered heterocyclyl, said C 3-10 cycloalkyl, or 3-10 membered heterocyclyl is optionally further substituted by one or more substituents selected from the group consisting of deuterium, halogen, hydroxy, C 1-4 alkyl, C 1-4 alkoxy, C 3-8 cycloalkyl, C 3-8 cycloalkyloxy, 3-8 membered heterocyclyl, and 3-8 membered heterocyclyloxy, said C 1-4 alkyl, C 3-8 cycloalkyl, or 3-8 membered heterocyclyl is optionally further more substituted by one or more substituents selected from the group consisting of deuterium, halogen, C 3-8 cycloalkyl, 3-8 membered heterocyclyl, hydroxy and C 1-4 alkoxy.