A compound of structural formula I: or a pharmaceutically acceptable salt thereof, wherein: X is selected from: -CF 2 -, -O- and -C -, Y is selected from: aryl, and heteroaryl, wherein aryl and heteroaryl are unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from R b; Z is selected from: -(CH 2) m P 2, -(CH 2) m P (C 1-6 alkyl), -(CH 2) m P (C 1-6 alkyl)(OC 1-6 alkyl), -(CH 2) m P (NRgC(R h) 2 CO 2 C 1-6 alkyl) 2 and wherein each CH 2 is unsubstituted or substituted with 1 or 2 substituents selected from C 1-6 alkyl, -OH and -NH 2 and wherein each alkyl is unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from R C; R 1 is selected from: -(CH 2) p aryl, biphenyl, -(CH 2) p heteroaryl, and -C 2-6 alkynyl-aryl, wherein each CH 2 is unsubstituted or substituted with 1 or 2 substituents selected from: halogen, CF3, -OH, -NH 2, -C 1-6 alkyl, -OC 1-6 alkyl, -NHC 1-6 alkyl, and -N(C 1-6 alkyl) 2, wherein each alkynyl is unsubstituted or substituted with 1, 2 or 3 substituents selected from: halogen, CF 3,-OH, -NH 2, -C 1-6 alkyl, -OC 1-6 alkyl, -NHC 1-6 alkyl, and -N(C 1-6 alkyl) 2, and wherein each phenyl, aryl and heteroaryl is unsubstituted or substituted with 1, 2, 3 or 4 substituents independently selected from R a; R2 is halogen; R 3, R 4 and R 5 are hydrogen; each R a is independently selected from the group consisting of: -C 1-6 alkyl, -OC 1-6 alkyl, -C 3-7 cycloalkyl, -C 2-6 cycloheteroalkyl and -aryl wherein alkyl, cycloalkyl, cycloheteroalkyl and aryl are unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from: oxo, -OH, -CN, -NH 2, -NH(C 1-6 alkyl), -N(C 1-6 alkyl) 2, -C 1-6 alkyl, -OC 1-6 alkyl, halogen, -CH 2 F, -CHF 2, -CF 3, -CO 2 H, -CO 2 C 1-6 alkyl, -C 3-7 cycloalkyl, phenyl and CH 2 phenyl; each R b is independently selected from hydrogen, -C 1-6 alkyl and -C 3-6 cycloalkyl wherein each alkyl and cycloalkyl is unsubstituted or substituted with 1, 2 or 3 halogens; R c is -C 1-6 alkyl wherein alkyl is unsubstituted; R g and R h is independently selected from: hydrogen, and C 1-6 alkyl, wherein alkyl is unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from: -OH, oxo, halogen, C 1-6 alkyl, -OC 1-6 alkyl, -NH 2, -NH(C 1-6 alkyl), and -N(C 1-6 alkyl) 2; R k and R m are each independently selected from -O-, and -NH-; each R p is independently selected from: aryl, and heteroaryl, wherein aryl and heteroaryl are unsubstituted or substituted with 1, 2 or 3 substituents selected from R w; each R w is independently selected from halogen, CN and C 1-6 alkyl wherein alkyl is unsubstituted; m is 0, 1, 2, 3 or 4; p is 0, 1, 2, or 3 and w is 0, 1, 2, 3 or 4. X is selected from: -CF 2 -, -O- and -C -, -CF 2 -, -O- and -C -, Y is selected from: aryl, and heteroaryl, wherein aryl and heteroaryl are unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from R b; aryl, and heteroaryl, Z is selected from: -(CH 2) m P 2, -(CH 2) m P (C 1-6 alkyl), -(CH 2) m P (C 1-6 alkyl)(OC 1-6 alkyl), -(CH 2) m P (NRgC(R h) 2 CO 2 C 1-6 alkyl) 2 and wherein each CH 2 is unsubstituted or substituted with 1 or 2 substituents selected from C 1-6 alkyl, -OH and -NH 2 and wherein each alkyl is unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from R C; -(CH 2) m P 2, -(CH 2) m P (C 1-6 alkyl), -(CH 2) m P (C 1-6 alkyl)(OC 1-6 alkyl), -(CH 2) m P (NRgC(R h) 2 CO 2 C 1-6 alkyl) 2 and R 1 is selected from: -(CH 2) p aryl, biphenyl, -(CH 2) p heteroaryl, and -C 2-6 alkynyl-aryl, wherein each CH 2 is unsubstituted or substituted with 1 or 2 substituents selected from: halogen, CF3, -OH, -NH 2, -C 1-6 alkyl, -OC 1-6 alkyl, -NHC 1-6 alkyl, and -N(C 1-6 alkyl) 2, wherein each alkynyl is unsubstituted or substituted with 1, 2 or 3 substituents selected from: halogen, CF 3,-OH, -NH 2, -C 1-6 alkyl, -OC 1-6 alkyl, -NHC 1-6 alkyl, and -N(C 1-6 alkyl) 2, and wherein each phenyl, aryl and heteroaryl is unsubstituted or substituted with 1, 2, 3 or 4 substituents independently selected from R a; -(CH 2) p aryl, biphenyl, -(CH 2) p heteroaryl, and -C 2-6 alkynyl-aryl, R2 is halogen; R 3, R 4 and R 5 are hydrogen; each R a is independently selected from the group consisting of: -C 1-6 alkyl, -OC 1-6 alkyl, -C 3-7 cycloalkyl, -C 2-6 cycloheteroalkyl and -aryl wherein alkyl, cycloalkyl, cycloheteroalkyl and aryl are unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from: oxo, -OH, -CN, -NH 2, -NH(C 1-6 alkyl), -N(C 1-6 alkyl) 2, -C 1-6 alkyl, -OC 1-6 alkyl, halogen, -CH 2 F, -CHF 2, -CF 3, -CO 2 H, -CO 2 C 1-6 alkyl, -C 3-7 cycloalkyl, phenyl and CH 2 phenyl; -C 1-6 alkyl, -OC 1-6 alkyl, -C 3-7 cycloalkyl, -C 2-6 cycloheteroalkyl and -aryl each R b is independently selected from hydrogen, -C 1-6 alkyl and -C 3-6 cycloalkyl wherein each alkyl and cycloalkyl is unsubstituted or substituted with 1, 2 or 3 halogens; R c is -C 1-6 alkyl wherein alkyl is unsubstituted; R g and R h is independently selected from: hydrogen, and C 1-6 alkyl, wherein alkyl is unsubstituted or substituted with 1, 2, 3 or 4 substituents selected from: -OH, oxo, halogen, C 1-6 alkyl, -OC 1-6 alkyl, -NH 2, -NH(C 1-6 alkyl), and -N(C 1-6 alkyl) 2; hydrogen, and C 1-6 alkyl, R k and R m are each independently selected from -O-, and -NH-; -O-, and -NH-; each R p is independently selected from: aryl, and heteroaryl, wherein aryl and heteroaryl are unsubstituted or substituted with 1, 2 or 3 substituents selected from R w; aryl, and heteroaryl, each R w is independently selected from halogen, CN and C 1-6 alkyl wherein alkyl is unsubstituted; m is 0, 1, 2, 3 or 4; p is 0, 1, 2, or 3 and w is 0, 1, 2, 3 or 4.