The present invention relates to new beta-agonists of general formula (I) wherein the groups R.sup.1 to R.sup.4 have the meanings given in ths claims and specification, the tautomers, racemates, enantiomers, diastereomers, solvates, hydrates, mixtures thereof, the prodrugs thereof and the salts thereof, particularly the physiologically acceptable salts thereof with inorganic or organic acids or bases, methods of preparing these compounds and their use as pharmaceutical compositions.