Compounds of the formula ##STR1## wherein R.sup.1 is halogen, C.sub.1-4 -alkyl, halo-(C.sub.1-4 -alkyl) or C.sub.2-4 -alkanoyl,R.sup.2 is hydrogen, hydroxy, C.sub.1-4 alkoxy, C.sub.1-4 -alkylthio or phenyl-(C.sub.1-4 -alkoxy) or , when X is O, also acyloxy,R.sup.3 is hydrogen or C.sub.1-4 -alkyl,R.sup.4 is a carbocyclic group or a heterocyclic group,R.sup.5 is hydrogen or fluorine,m stands for zero, 1 or 2,X is O or NH and Y is a direct bond, --CH.dbd.CH--, --C.tbd.C-- or a group of the formula of--(Z).sub.n --A-- (a)in which A is a C.sub.1-8 alkylene group which is optionally substituted by one or two phenyl groups,Z is O, S, SO or SO.sub.2 and n stands for zero or 1, with the proviso that R.sup.1 is different from iodine, when R.sup.2 is hydroxy or benzoyloxy, R.sup.3 is hydrogen,R.sup.4 is unsubstituted phenyl, R.sup.5 is hydrogen, m stands for zero, X is O, and Y is a direct bond, and tautomers thereof, which possess antiviral activity and can therefore be used in the form of medicaments for the control and prevention of viral infections are described. The compounds of formula I can be prepared according to known methods.