Cyclopentane compounds

A compound of Formula I

• wherein:
• X is a) O, and R1 is a 6-membered aromatic or heteroaromatic ring selected from phenyl, pyridyl, pyrimidyl, pyrazinyl or pyridazyl, wherein R1 is optionally substituted with one or two substituents Y independently selected from F, Cl, Br, CN, OH, OC1-3alkyl, OCF3, C1-3alkyl, C(O)NH2, CF3 or cyclopropyl;
• or b) NR2, and wherein N, R1 and R2 together form a 5-membered aromatic heterocycle that is optionally substituted with one or two substituents Y that are independently selected from F, Cl, CN, or Me;
• R3 is independently selected from F, Cl, CN, methyl, methoxy, hydroxy and ethynyl;
• R4 is independently selected from F or Cl attached to C2, C4 or C5 of the piperidine ring;
• and
• the integers a and b are independently selected from 0, 1 or 2;
• or a pharmaceutically acceptable salt thereof.