The present invention is directed to compounds useful for treating addictive behavior and sleep disorders represented by structural Formula (I) ##STR00001## or pharmaceutically acceptable salt forms thereof, wherein R.sup.1, R.sup.5, R.sup.6a, R.sup.6b, R.sup.7, R.sup.8, R.sup.9, X, b, k, m, and n, and the dashed lines are described herein. The compounds used in the method of treatment of this invention are serotonin agonists and antagonists and are useful in the control or prevention of central nervous system disorders including addictive behavior and sleep disorders.