The invention concerns novel compounds of the formula I ##STR1## wherein R.sup.1 is selected from hydrogen, alkyl, alkenyl, alkynyl, substituted alkyl, acyl, alkylsulfonyl, benzenesulfonyl, substituted benzenesulfonyl, and an inorganic or organic cation;R.sup.2 is selected from alkyl, alkenyl, alkynyl, substituted alkyl, haloalkenyl and haloalkynyl;R.sup.3 is selected from alkyl, fluoroalkyl, alkenyl, alkynyl and phenyl; andn is an integer chosen from 2 to 5.The compounds are cereal selective herbicides and in further embodiments of the invention provides processes for the preparation of compounds of formula I, intermediates useful in the preparation of compounds of formula I, herbicidal compositions containing as active ingredient a compound of formula I, and processes for severely damaging or killing unwanted plants by applying to the plants or to the growth medium of the plants an effective amount of a compound of formula I.