The present invention relates to a compound of formula (I): wherein: R8 and R9, independently of each other, are hydrogen, fluorine or C1-C3alkyl; R10 is hydrogen or methyl (preferably hydrogen); and the other substituents are as defined herein; and wherein the compound of formula (I) is optionally present as an agrochemically acceptable salt thereof. These compounds are thought to be 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.