The invention provides compounds of the general formula (I) ##STR1## and physiologically acceptable salts and solvates thereof, wherein Q represents a chlorine atom or a trifluoromethyl group; X represents a bond, or a C.sub.1-6 alkylene, C.sub.2-6 alkenylene or C.sub.2-6 alkynylene chain, and Y represents a bond, or a C.sub.1-6 alkylene, C.sub.2-6 alkenylene or C.sub.2-6 alkynylene chain with the proviso that the sum total or carbon atoms in the chains X and Y is not more than 10, and the chains XCH.sub.2 and CH.sub.2 Y may each be optionally substituted by one or two C.sub.1-3 alkyl groups, or, when one carbon atom is substituted by two alkyl groups, these may be linked to form an alkylene group; R represents a hydrogen atom or a C.sub.1-3 alkyl group; R.sup.1 and R.sup.2 each represent a hydrogen atom or a C.sub.1-3 alkyl group, with the proviso that the sum total of carbon atoms in R.sup.1 and R.sup.2 is not more than 4; and Het is optionally substituted pyrimidinyl. The compounds have a stimulant action at .beta.-adrenoreceptors and may be used in the treatment of diseases associated with reversible airways obstruction such as asthma and chronic bronchitis.