The present invention provides compounds of formula I: a stereoisomer or a pharmaceutically acceptable salt thereof, wherein the variables R1, R2, R3, R4, X and n are defined as defined herein. Additionally, a method for treating dopamine-related neurological disorders selected form the group consisting of neurological, psychological, cardiovascular, cognitive or attention disorders, substance abuse and addictive behavior, or a combination thereof, comprising administering to a patient in need of such treatment a therapeutically effective amount of compounds of formula I.