The present invention relates to compounds of formula I wherein R.sup.1 is selected from the group consisting of hydrogen and lower alkyl; each R.sup.2 is independently selected from the group consisting of hydrogen and lower alkyl; each R.sup.3 is independently selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, phenyloxy, benzyloxy, halogen and lower alkyl substituted by halogen; X is selected from the group consisting of --CH.sub.2--, --CH-- and --O--; Y is selected from the group consisting of --CH.sub.2--, --CH-- and a bond with the proviso that, when X is --O--, Y may not be a bond; Z is selected from the group consisting of --CH.sub.2-- and --CH--; m is 0, 1 or 2; and n is 0, 1 or 2;and to pharmaceutically-acceptable acid addition salts of such compounds. The invention relates also to processes for preparing such compounds, compositions comprising such a compound or a pharmaceutically-acceptable acid addition salt thereof, and a method of treating a disease or disorder in a patient comprising administering such a compound, or pharmaceutically-acceptable acid addition salt thereof, to a patient in need of such treatment.