Compounds of formula (I) and salts are provided: wherein R.sup.5 is selected from halogen, C.sub.1-6alkyl, C.sub.1-6alkyl substituted with one or more fluorine atoms, C.sub.1-6 alkoxy, C.sub.1-6 alkoxy substituted with one or more fluorine atoms, and cyano; R.sup.6 is selected from halogen, C.sub.1-6alkyl, C.sub.1-6alkyl substituted with one or more fluorine atoms, C.sub.3-6cycloalkyl, C.sub.3-6cycloalkyl substituted with one or more fluorine atoms, C.sub.1-6 alkoxy, C.sub.1-6 alkoxy substituted with one or more fluorine atoms, and cyano; and Q is hydrogen or C.sub.1-6alkyl. The compounds are M.sub.1 agonists and are useful for therapy, for example in the treatment of psychotic disorders and cognitive impairment.