Compounds of the general formula (I) ##STR1## and physiologically acceptable salts and solvates thereof, which have .beta..sub.2 -adrenoreceptor stimulant activity. They may be used in the treatment of diseases associated with reversible airways obstruction, such as asthma and chronic bronchitis. In preferred embodiments, Q represents a chlorine atom or a trifluoromethyl group, X represents a C.sub.3-4 alkylene chain, Y a C.sub.1-5 alkylene chain, R, R.sup.1 and R.sup.2 are each preferably a hydrogen atom or a methyl group and Het represents a pyrimidinyl pyrazinyl, triazinyl, thiazolyl, quinolinyl, benzimidazolyl, benzothiazolyl, benzoxazolyl or pyridyl group.