Abstract: Compounds of formula I ##STR1## wherein R.sub.1 is hydrogen, C.sub.1 -C.sub.8 alkyl, C.sub.5 -C.sub.8 cycloalkyl or C.sub.7 -C.sub.9 phenylalkyl, A.sub.1 and A.sub.4 are phenyl, ##STR2## or phenyl which is substituted by 1 to 3 radicals R.sub.3, which radicals R.sub.3 are each independently of one another selected from the group consisting of C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.18 alkoxy, C.sub.3 -C.sub.4 alkenyloxy, C.sub.7 -C.sub.9 phenylalkoxy, C.sub.5 -C.sub.8 cycloalkoxy, C.sub.1 -C.sub.18 alkanoyloxy, C.sub.3 -C.sub.18 alkenoyloxy, benzoyloxy, phenoxy and hydroxy, m is 1 or 2, A.sub.2 and A.sub.3, together with the linking carbon atom, form a C.sub.5 -C.sub.7 cycloalkylidene ring which is unsubstituted or substituted by 1 to 3 C.sub.1 -C.sub.4 alkyl groups, are very suitable for stabilising organic materials against thermal, oxidative or light-induced degradation.