A compound of Formula I or a pharmaceutically acceptable salt thereof; wherein Y is a five membered heteroaryl comprising one to four heteroatoms each of which is independently selected from the group consisting of N, O and S n; wherein the heteroaryl is optionally substituted with one to three substituents each of which is independently selected from the group consisting of halo, C 1 -C 6 alkyl and C 1 -C 6 haloalkyl; Z is phenyl, optionally substituted with one to three halo; R 1a and R 1b are each independently selected from the group consisting of -H, -OH, halo, C 1 -C 6 alkyl optionally substituted with one to three substituents each of which is independently selected from the group consisting of halo, -OH, C 1 -C 3 alkoxy, C 3 -C 7 cycloalkyl and a four to seven membered heterocycloalkyl comprising one to three heteroatoms each of which is independently selected from the group consisting of N, O and S n, C 3 -C 7 cycloalkyl optionally substituted with one to three substituents each of which is independently selected from the group consisting of -OH, halo and C 1 -C 6 alkyl, and four to seven membered heterocycloalkyl comprising one to three heteroatoms each of which is independently selected from the group consisting of N, O and S n; and wherein the four to seven membered heterocycloalkyl is optionally substituted with one to three substituents each of which is independently selected from the group consisting of -OH, halo and C 1 -C 6 alkyl; or R 1a and R 1b taken together with the carbon to which they are attached form a C 3 -C 7 cycloalkyl or a four to seven membered heterocycloalkyl comprising one to three heteroatoms each of which is independently selected from the group consisting of N, O and S n; and wherein the C 3 -C 7 cycloalkyl or four to seven membered heterocycloalkyl are optionally substituted with one to three substituents each of which is independently selected from the group consisting of -OH, halo and C 1 -C 6 alkyl; and n at each occurrence is independently 0, 1 or 2. Y is a five membered heteroaryl comprising one to four heteroatoms each of which is independently selected from the group consisting of N, O and S n; wherein the heteroaryl is optionally substituted with one to three substituents each of which is independently selected from the group consisting of halo, C 1 -C 6 alkyl and C 1 -C 6 haloalkyl; Z is phenyl, optionally substituted with one to three halo; R 1a and R 1b are each independently selected from the group consisting of -H, -OH, halo, C 1 -C 6 alkyl optionally substituted with one to three substituents each of which is independently selected from the group consisting of halo, -OH, C 1 -C 3 alkoxy, C 3 -C 7 cycloalkyl and a four to seven membered heterocycloalkyl comprising one to three heteroatoms each of which is independently selected from the group consisting of N, O and S n, C 3 -C 7 cycloalkyl optionally substituted with one to three substituents each of which is independently selected from the group consisting of -OH, halo and C 1 -C 6 alkyl, and four to seven membered heterocycloalkyl comprising one to three heteroatoms each of which is independently selected from the group consisting of N, O and S n; and wherein the four to seven membered heterocycloalkyl is optionally substituted with one to three substituents each of which is independently selected from the group consisting of -OH, halo and C 1 -C 6 alkyl; or R 1a and R 1b taken together with the carbon to which they are attached form a C 3 -C 7 cycloalkyl or a four to seven membered heterocycloalkyl comprising one to three heteroatoms each of which is independently selected from the group consisting of N, O and S n; and wherein the C 3 -C 7 cycloalkyl or four to seven membered heterocycloalkyl are optionally substituted with one to three substituents each of which is independently selected from the group consisting of -OH, halo and C 1 -C 6 alkyl; and n at each occurrence is independently 0, 1 or 2.