The present invention relates to novel reactive dyes of the formula (I) where R1 to R4 are independently hydrogen, C1–C8-alkyl, C2–C8-alkyl, wherein nonadjacent CH2 groups may be replaced by oxygen atoms or imino or C1–C4-alkylimino groups and/or CH2 groups by carbonyl groups, C2–C8-alkenyl, aryl, arylalkylene or a moiety containing a reactive group or the precursor of a reactive group, with the proviso that at least one of R1 to R4 is a moiety which contains a reactive group or the precursor of a reactive group. The present invention further relates to the use of the reactive dyes of the formula (I) for dyeing substrates containing nucleophilic groups and to preparations containing at least one reactive dye of the formula (I).