The compounds of formula I: ##STR1## wherein R.sup.1 and R.sup.2 are, independently, hydrogen, alkyl, phenyl or benzyl; or R.sup.1 and R.sup.2, taken together, are benzylidene optionally substituted with R.sup.3 as defined below or alkylidene, or R.sup.1 and R.sup.2, taken together with the carbon to which they are attached, form a carbonyl moiety or a cycloalkyl group; R.sup.3 is hydrogen, hydroxy, halo, trifluoromethyl, trifluoromethoxy, alkyl, alkoxy, aralkoxy, alkanoyloxy, amino, mono- or di-alkylamino, alkanamido or alkanesulfonamido; R.sup.4 is hydrogen or alkyl; m is an integer 0, 1 or 2; n is an integer from 0 to 6, inclusive; Z is hydrogen, hydroxy, alkyl, alkenyl, alkynyl, alkoxy, cycloalkyl, polycyclo-alkyl, phenyl optionally substituted with R.sup.3 as defined above, phenoxy optionally substituted with R.sup.3 as defined above, naphthyl optionally substituted with R.sup.3 as defined above or naphthyloxy optionally substituted with R.sup.3 as defined above, heteroaryl or heteroaryloxy, in which the heterocyclic ring of the heteroaryl or heteroaryloxy group is selected from thiophene, furan, pyridine, pyrazine, pyrimidine, indole, indazole, imidazole, chroman, coumarin, carbostyril, quinoline, benzisoxazole, benzoxazole, pyrazole, pyrrole, thiazole, oxazole, or isoxazole and the heterocyclic ring is optionally substituted by R.sup.3 as defined above; or a pharmaceutically acceptable salt thereof, are useful in treating disorders of the dopaminergic system.