A compound of Formula, or a pharmaceutically acceptable salt thereof: wherein R 1 is selected from the group consisting of H, CH 3, F, Cl, and NH 2; R 2 is selected from the group consisting of F, Cl, OH, NH 2, CN, and N 3; R 3 is selected from the group consisting of CN, N 3, methyl, ethyl, propyl, vinyl, propenyl, ethynyl, CH 2 F, CHF 2, CH 2 Cl, CH 2 SMe, and CH 2 OMe; and R4 is (a) H; (b) selected from the group consisting of:; or (c) a group of the formula wherein: R 8 is selected from phenyl, 1-naphthyl, 2-naphthyl, R 9 is selected from H and CH 3; R 10 is selected from H or C 1 -C 6 alkyl; and R 11 is selected from H, C 1 -C 8 alkyl, benzyl, C 3 -C 6 cycloalkyl, and -CH 2 -C 3 -C 6 cycloalkyl; or (d) a group of the formula wherein: R 8 is selected from phenyl, 1-naphthyl, 2-naphthyl, R 9 is selected from H and CH 3; R 10 is selected from H or C 1 -C 6 alkyl; and R 11 is selected from H, C 1 -C 8 alkyl, benzyl, C 3 -C 6 cycloalkyl, and -CH 2 -C 3 -C 6 cycloalkyl; or (e) a group of the formula wherein n' is selected from 1, 2, 3, and 4; and R 7 is selected from the group of C 1 -C 8 alkyl, -O-C 1 -C 8 alkyl, benzyl, -O-benzyl, -CH 2 -C 3 -C 6 cycloalkyl, -O-CH 2 -C 3 -C 6 cycloalkyl, and CF 3. R 2 is selected from the group consisting of F, Cl, OH, NH 2, CN, and N 3; R 3 is selected from the group consisting of CN, N 3, methyl, ethyl, propyl, vinyl, propenyl, ethynyl, CH 2 F, CHF 2, CH 2 Cl, CH 2 SMe, and CH 2 OMe; and R4 is (a) H; (b) selected from the group consisting of:; or (c) a group of the formula wherein: R 8 is selected from phenyl, 1-naphthyl, 2-naphthyl, R 9 is selected from H and CH 3; R 10 is selected from H or C 1 -C 6 alkyl; and R 11 is selected from H, C 1 -C 8 alkyl, benzyl, C 3 -C 6 cycloalkyl, and -CH 2 -C 3 -C 6 cycloalkyl; or (d) a group of the formula wherein: R 8 is selected from phenyl, 1-naphthyl, 2-naphthyl, R 9 is selected from H and CH 3; R 10 is selected from H or C 1 -C 6 alkyl; and R 11 is selected from H, C 1 -C 8 alkyl, benzyl, C 3 -C 6 cycloalkyl, and -CH 2 -C 3 -C 6 cycloalkyl; or (e) a group of the formula wherein n' is selected from 1, 2, 3, and 4; and R 7 is selected from the group of C 1 -C 8 alkyl, -O-C 1 -C 8 alkyl, benzyl, -O-benzyl, -CH 2 -C 3 -C 6 cycloalkyl, -O-CH 2 -C 3 -C 6 cycloalkyl, and CF 3. (a) H; (b) selected from the group consisting of:; or (c) a group of the formula wherein: R 8 is selected from phenyl, 1-naphthyl, 2-naphthyl, R 9 is selected from H and CH 3; R 10 is selected from H or C 1 -C 6 alkyl; and R 11 is selected from H, C 1 -C 8 alkyl, benzyl, C 3 -C 6 cycloalkyl, and -CH 2 -C 3 -C 6 cycloalkyl; or R 8 is selected from phenyl, 1-naphthyl, 2-naphthyl, R 9 is selected from H and CH 3; R 10 is selected from H or C 1 -C 6 alkyl; and R 11 is selected from H, C 1 -C 8 alkyl, benzyl, C 3 -C 6 cycloalkyl, and -CH 2 -C 3 -C 6 cycloalkyl; or (d) a group of the formula wherein: R 8 is selected from phenyl, 1-naphthyl, 2-naphthyl, R 9 is selected from H and CH 3; R 10 is selected from H or C 1 -C 6 alkyl; and R 11 is selected from H, C 1 -C 8 alkyl, benzyl, C 3 -C 6 cycloalkyl, and -CH 2 -C 3 -C 6 cycloalkyl; or R 8 is selected from phenyl, 1-naphthyl, 2-naphthyl, R 9 is selected from H and CH 3; R 10 is selected from H or C 1 -C 6 alkyl; and R 11 is selected from H, C 1 -C 8 alkyl, benzyl, C 3 -C 6 cycloalkyl, and -CH 2 -C 3 -C 6 cycloalkyl; or (e) a group of the formula