The present invention is directed to novel compounds of the formula (I) ##STR00001## wherein X, R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are as described in the specification, processes for the preparation of and pharmaceutical compositions comprising said derivatives. The compounds of the present invention are useful for the treatment of epilepsy. The invention is further directed to a process for the preparation of compounds of formula (XX), ##STR00002## wherein X, R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are as described in the specification.