Compounds of general formula (1) ##STR1## are described wherein Y is a halogen atom or a group --OR.sup.1, wherein R.sup.1 is an optionally substituted alkyl group; X is --O--, --S--, or --N(R.sup.6), wherein R.sup.6 is a hydrogen atom or an optionally substituted alkyl group; R.sup.2 is an optionally substituted cycloalkyl or cycloalkenyl group; R.sup.3 and R.sup.4, which may be the same or different, is each a hydrogen atom or an optionally substituted alkyl, --CO.sub.2 R.sup.7 (wherein R.sup.7 is a hydrogen atom, am optionally substituted alkyl, aralkyl, aryl, aryloxyalkyl, alkanoyloxyalkyl or aroyloxyalkyl group), --CONR.sup.8 R.sup.9 (where R.sup.8 and R.sup.9, which may be the same or different, is as defined for R.sup.7), --CSNR.sup.8 R.sup.9, --CN or --CH.sub.2 CN group; Z is --(CH.sub.2).sub.n -- where n is zero or an integer 1, 2 or 3; R.sup.5 is an optionally substituted monocyclic or bicyclic aryl group optionally containing one oremore heteroatoms selected from oxygen, sulphur or nitrogen atoms; and the salts, solvates, hydrates, prodrugs and N-oxides thereof. Compounds according to the invention are potent and selective phosphodiesterase type IV inhibitors and are useful in the prophylaxis and treatment of diseases such as asthma where an unwanted inflammatory response or muscular spasm is present.