The invention is concerned with compounds of the formula ##STR1## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 have the significances given in the description, as well as enol ethers and salts thereof and their manufacture. The compounds have herbicidal properties and are accordingly suitable as active ingredients of weed control compositions. The invention is also concerned with weed control compositions containing one or more of such substances and with the use of the substances or compositions for the control of weeds.