The present invention provides a composition comprising a compound of formula I: or a pharmaceutically acceptable salt thereof, wherein each of R.sup.1, R.sup.2, R.sup.3, y, 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. Such compounds, and compositions thereof, are useful for treating a variety of central nervous system disorders such as schizophrenia.