Herbicidal compounds of the formula: ##STR1## where X is oxygen or sulfur; R.sub.1 is methyl or ethyl; R.sub.2 is alkyl of 1-4 carbon atoms, methoxy or cyanomethyl; and R.sub.1 and R.sub.2 together can be (CH.sub.2).sub.4 ; provided that when R.sub.2 is alkyl of 3 or 4 carbon atoms, methoxy or cyanomethyl, R.sub.1 cannot be ethyl.
式子如下:##STR1## 其中X为氧或
硫;R.sub.1为甲基或乙基;R.sub.2为1-4个碳原子的烷基,甲氧基或
氰甲基;且当R.sub.2为3或4个碳原子的烷基,甲氧基或
氰甲基时,R.sub.1不能为乙基。