A compound of the formula: wherein R 1 is aryl, heteroaryl, C 3-6 cycloalkyl or heterocyclyl, wherein said aryl, heteroaryl, cycloalkyl and heterocyclyl groups are optionally substituted with one to three substituents independently selected from the group consisting of halo, nitro, cyano, oxo, R 4, OR 4, (C=O)R 4, (C=O)OR 4, NR 4 R 5, NH(C=O)R 4, NH(C=O)OR 4, C NR 4 R 5, C 3-6 cycloalkyl and heteroaryl which is optionally substituted with R 4; R 2 is hydrogen or CH(R 2a)(R 2b); R 2a is hydrogen, C 1-6 alkyl, aryl, heteroaryl, C 3-6 cycloalkyl or heterocyclyl, wherein said alkyl group is optionally substituted with one to three substituents independently selected from the group consisting of halo, hydroxy and cyano, and wherein said aryl, heteroaryl, cycloalkyl and heterocyclyl groups are optionally substituted with one to three substituents independently selected from the group consisting of halo, nitro, cyano, oxo, R 4 and OR 4; R 2b is hydrogen or C 1-6 alkyl, which is optionally substituted with one to three substituents independently selected from the group consisting of halo, hydroxy and cyano; R 3 is halo, cyano, (C=O)OR 4 or R 6; R 4 is hydrogen or C 1-6 alkyl, which is optionally substituted with one to three groups independently selected from the group consisting of halo, hydroxy and methoxy; R 5 is hydrogen or C 1-6 alkyl, which is optionally substituted with one to three groups independently selected from the group consisting of halo and hydroxy; R 6 is aryl, heteroaryl, C 3-10 cycloalkyl or heterocyclyl, wherein said aryl, heteroaryl, cycloalkyl and heterocyclyl groups are optionally substituted with one to three substituents independently selected from the group consisting of halo, nitro, cyano, oxo, R 4, OR 4, (C=O)R 4, (C=O)OR 4, (C=O)NR 4 R 5, (C=O)(C=O)NR 4 R 5, (C=O)R 7, (C=O)OR 7, (C=O)CH 2 R 7, (C=O)NHCH 2 R 7 (C=O)NR 4 R 7, NR 4 R 7, NH(C=O)R 4, NH(C=O)OR 4, SO 2 R 4, SO 2 NR 4 R 5, NR 4 SO 2 R 5 and PO 3 R 4; R 7 is C 3-6 cycloalkyl, C 5-6 cycloalkenyl or heterocyclyl, wherein said cycloalkyl, cycloalkenyl and heterocyclyl groups are optionally substituted with one to three substituents independently selected from the group consisting of halo, oxo and R 4; R a is hydrogen, halo, hydroxy or methyl; or a pharmaceutically acceptable salt thereof. wherein R 1 is aryl, heteroaryl, C 3-6 cycloalkyl or heterocyclyl, wherein said aryl, heteroaryl, cycloalkyl and heterocyclyl groups are optionally substituted with one to three substituents independently selected from the group consisting of halo, nitro, cyano, oxo, R 4, OR 4, (C=O)R 4, (C=O)OR 4, NR 4 R 5, NH(C=O)R 4, NH(C=O)OR 4, C NR 4 R 5, C 3-6 cycloalkyl and heteroaryl which is optionally substituted with R 4; R 2 is hydrogen or CH(R 2a)(R 2b); R 2a is hydrogen, C 1-6 alkyl, aryl, heteroaryl, C 3-6 cycloalkyl or heterocyclyl, wherein said alkyl group is optionally substituted with one to three substituents independently selected from the group consisting of halo, hydroxy and cyano, and wherein said aryl, heteroaryl, cycloalkyl and heterocyclyl groups are optionally substituted with one to three substituents independently selected from the group consisting of halo, nitro, cyano, oxo, R 4 and OR 4; R 2b is hydrogen or C 1-6 alkyl, which is optionally substituted with one to three substituents independently selected from the group consisting of halo, hydroxy and cyano; R 3 is halo, cyano, (C=O)OR 4 or R 6; R 4 is hydrogen or C 1-6 alkyl, which is optionally substituted with one to three groups independently selected from the group consisting of halo, hydroxy and methoxy; R 5 is hydrogen or C 1-6 alkyl, which is optionally substituted with one to three groups independently selected from the group consisting of halo and hydroxy; R 6 is aryl, heteroaryl, C 3-10 cycloalkyl or heterocyclyl, wherein said aryl, heteroaryl, cycloalkyl and heterocyclyl groups are optionally substituted with one to three substituents independently selected from the group consisting of halo, nitro, cyano, oxo, R 4, OR 4, (C=O)R 4, (C=O)OR 4, (C=O)NR 4 R 5, (C=O)(C=O)NR 4 R 5, (C=O)R 7, (C=O)OR 7, (C=O)CH 2 R 7, (C=O)NHCH 2 R 7 (C=O)NR 4 R 7, NR 4 R 7, NH(C=O)R 4, NH(C=O)OR 4, SO 2 R 4, SO 2 NR 4 R 5, NR 4 SO 2 R 5 and PO 3 R 4; R 7 is C 3-6 cycloalkyl, C 5-6 cycloalkenyl or heterocyclyl, wherein said cycloalkyl, cycloalkenyl and heterocyclyl groups are optionally substituted with one to three substituents independently selected from the group consisting of halo, oxo and R 4; R a is hydrogen, halo, hydroxy or methyl; or a pharmaceutically acceptable salt thereof.