The present invention relates to imidazole derivatives of formula I wherein R1, R2, R3, R4, X, Y and R are described hereinabove, or a pharmaceutically acceptable salt thereof. The invention also relates to a pharmaceutical composition comprising the imidazole derivatives of formula I, a process for preparing a compound of formula I, and a method of treating or preventing acute and/or chronic neurological disorder comprising administering to a patient in need of such treatment and/or prevention a therapeutically effective amount of said pharmaceutical composition. These disorders include Alzheimer's disease. These disorders also include mild cognitive impairment.