The present invention relates to compounds of formula I: ##STR00001## wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are as defined in the specification and claims, which compounds are active on the GABA.sub.B receptor and are useful in the control or prevention of CNS illnesses, especially of illnesses and disorders comprising anxiety, depression, epilepsy, schizophrenia, and cognitive disorders.