The present invention relates to a compound of formula (I) wherein: R1 is C1-C3alkoxy, C1-C2alkoxy-C1-C3alkoxy, C1-C2fluoroalkoxy, ethyl, n-propyl, n-butyl, cyclopropyl or ethynyl; R2 is hydrogen, ethyl, n-propyl, cyclopropyl, vinyl, ethynyl, C1-C3alkoxy, C1-C3fluoroalkyl, C1-C2fluoroalkoxy, C1-C2alkoxy-C1-C3alkoxy-, or C1fluoroalkoxy-C1-C3alkoxy-; provided that when R1 is ethyl, n-propyl, n-butyl, cyclopropyl or ethynyl, then R2 is hydrogen, ethyl, n-propyl, cyclopropyl, vinyl or ethynyl; and Y is O, S, S(O), S(O)2, N(C1-C2alkyl), N(C1-C2alkoxy), C(O), CR8R9 or —CR10R11CR12R13—; and G, R3, R4, R5 and R6 are as defined herein; wherein the compound of formula (I) is optionally present as an agrochemically acceptable salt thereof. These compounds are suitable for use as herbicides. The invention therefore also relates to a method of controlling weeds, especially grassy monocotyledonous weeds, in crops of useful plants, comprising applying a compound of formula (I), or a herbicidal composition comprising such a compound, to the plants or to the locus thereof.