The present invention provides compounds of formula I ##STR00001## pharmaceutically acceptable salts thereof, and pharmaceutical compositions thereof, which are antagonists of the 5-HT.sub.6 receptor. The present invention further provides a method of treating disorders associated with 5-HT.sub.6 receptors, including schizophrenia, anxiety, Alzheimer's disease, and cognitive disorders selected from the group consisting of age-related cognitive decline, mild cognitive impairment, and dementia, comprising: administering to a patient in need thereof an effective amount of a compound of formula I.