Abstract: Pharmaceutical compounds of the formula ##STR1## in which R.sup.1 is hydrogen or halo, and R.sup.2 is C.sub.1-10 alkyl, C.sub.2-10 alkenyl, C.sub.2-10 alkynyl, C.sub.3-6 cycloalkyl optionally substituted by 1 to 3 C.sub.1-4 alkyl groups, C.sub.3-6 cycloalkyl-C.sub.1-4 alkyl in which the cycloalkyl group is optionally substituted by 1 to 3 C.sub.1-4 alkyl groups, or optionally substituted phenyl-C.sub.1-4 alkyl; or a salt thereof. Such compounds are useful for treating a disorder of the central nervous system which is associated with the modulation of a 5-HT.sub.3 receptor.