Compounds of formula I or pharmaceutically acceptable salts thereof are provided: wherein each of R.sup.1, R.sup.1', R.sup.2, R.sup.3, R.sup.4, n, and Ar are as defined, and described in classes and subclasses herein, which are agonists or partial agonists of the 2C subtype of brain serotonin receptors. The compounds, and compositions containing the compounds, can be used to treat a variety of central nervous system disorders such as schizophrenia.