The invention relates to compounds of formula (I), and their use as herbicides. In said formula, R1 to R6 represent groups such as hydrogen, halo-gen or organic groups such as alkyl, alkenyl, alkynyl, or alkoxy; W is a bicyclic heterocycle; X is a bond or a divalent unit; Y is hydrogen, cyano, hydroxyl or a linear or cyclic organic group. The invention further refers to a composition comprising such compound and to the use thereof for controlling unwanted vegetation.