The invention relates to compounds of general formula (I) and physiologically acceptable salts and solvates thereof, methods for their preparation and pharmaceutical formulations thereof. ##STR1## wherein Ar represents a substituted phenyl or nitrogen-containing heterocyclic ring; X and Y represent alkylene, alkenylene or alkynylene chains; R.sup.1, R.sup.2 and R.sup.18 each represent hydrogen or alkyl groups; and Q represents an optionally substituted furan or thiophene ring. The compounds of the invention have a stimulant action at .beta..sub.2 -adrenoreceptors and are useful in the treatment of diseases associated with reversible airways obstruction such as asthma and chronic bronchitis.