A compound of formula (1) wherein R1 represents a phenyl derivative of formula (a) or (b). R2 is selected from the group consisting of 1-2C-alkoxy and 1-2C-alkoxy which is completely or predominantly substituted by fluorine R3 is selected from the group consisting of 1-2C-alkoxy, 3-5C-cycloalkoxy, 3-5C-cycloalkylmethoxyand 1-2C-alkoxy which is completely or predominantly substituted by fluorine R4 is selected from the group consisting of 1-2C-alkoxy and 1-2C-alkoxy which is completely or predominantly substituted by fluorine R5 is 1-2C-alkyl and R6 is selected from the group consisting of hydrogen and 1-2C-alkyl or R5 and R6 together and with inclusion of the two carbon atoms, to which they are bonded, form a spiro-linked 5- or 6-membered hydrocarbon ring R7 is 1-3C-alkyl and R8 is 1-3C-alkyl or R7 and R8 together with the carbon atom, to which they are bonded, form a spiro-linked 3-, 4-, 5- or 6-membered hydrocarbon ring, R9 is-N(R11)R12, R11 and R12 together and with inclusion of the nitrogen atom to which they are bonded, form a heterocyclic ring selected from the group consisting of a pyrrolidin-2,5-dione-1-yl-, isoindol-1,3-dione-2-yl-, 2-oxo-2,3-dihydro-1 H-indol-1-yl-, pyrrolidin-2-one-1-yl-, piperidin-2,6-dione-1-yl-,morpholin-3,5-dione-4-yl-, thiomorpholin-3,5-dione-4-yl-, thiomorpholine-1-oxide-3,5-dione-4-yl- and a thiomorpholine-1, 1-dioxide-3,5-dione-4-yl-ring and n is 1 or 2 or a stereoisomer of the compound. The compound is used as a phosphodiesterase type 4 (PDE4) inhibitor for treatment of acute or chronic airway diseases and for the treatment or prophylaxis of allergic rhinitis. An example of the compound of formula 1 is 1-(2-{ 4-[3-(3,4-dimethoxyphenyl)-4,4-dimethyl-5-oxo-4,5-dihydro-1H-pyrazol-1-yl]piperidin-1-yl} -2-oxoethyl)pyrrolidine-2,5-dione.
