Compounds of formula (I) ##STR1## wherein one of X and Y represents nitrogen, and the other of X and Y represents oxygen, sulphur or N--R.sup.2 ; Q represents a substituted five- or six- membered monocyclic heteroaliphatic ring which contains one nitrogen atom as the sole heteroatom and is linked to the five-membered heteroatomic ring containing the moieties X and Y via a carbon atom; as well as substituted 1,3-dioxopropane precursors thereto, are ligands for dopamine receptor subtypes within the body and are therefore useful in the treatment of disorders of the dopamine system, in particular schizophrenia.