The present invention relates to compounds of formula (I) ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are as defined in the description and claims, and pharmaceutically acceptable salts thereof, for use as therapeutically active substances. The compounds are useful for the treatment and/or prophylaxis of diseases which are associated with the modulation of CB1 receptors, including obesity.