Disclosed are compounds of the formula: ##STR00001## and the pharmaceutically acceptable salts thereof, wherein W, Q, X, X.sub.1, Y and Z are as defined herein. These compounds bind with high selectivity and/or high affinity to the benzodiazepine site of GABA.sub.A receptors and are therefore useful in the treatment of central nervous system (CNS) diseases and as probes for the localization of GABA.sub.A receptors in tissue samples. Also disclosed are intermediates useful in the preparation of these compounds.