Ar is

(1) phenyl,

(2) naphthyl,

(3) a 5- to 10-membered monocyclic or bicyclic heterocyclic ring having 1 to 4 heteroatoms selected from the group consisting of oxygen, sulfur, or nitrogen, or

(4) —R⁹-phenyl;

wherein the phenyl, naphthyl, or heterocyclic ring is optionally substituted with halogen, C_1-6 alkyl, CF₃, hydroxyl, C_1-6 alkoxyl, OCF₃, COCF₃, CN, NO₂, phenyloxy, phenyl, C_1-6 alkylsulfonyl, C_2-6 alkenyl, —NR⁷R⁸, C_1-6 alkylcarboxyl, formyl, —C_1-6 alkyl-NH—CO-phenyl, —C_1-6 alkyl-CO—NH-phenyl, —NH—CO—C_1-6 alkyl, —CO—NR⁷R⁸, or SR⁷; wherein each of R⁷ and R⁸ is independently H or C_1-6 alkyl; and R⁹ is C_1-6 alkylidene or C_2-6 alkenylene, either of which is optionally substituted with phenyl or phenyloxy;

R² is H, phenyl, I, or C_1-6 alkyl;

R³ is H or 3-(1-azabicyclo[2.2.2]oct-2-en)yl;

R⁴ is H or is selected from the group consisting of:

wherein R⁶ is H, C_1-6 alkyl, or benzyl; and

R⁵ is H, hydroxy, C_1-3 alkoxy, F, NO₂, CF₃, OCF₃, or is selected from the group consisting of:

or a pharmaceutically acceptable salt, hydrate, or stereoisomer thereof,

with the proviso that when R² is alkyl, R⁴ is not H.