The present invention relates to compounds represented by the general formula (I): ##STR1## wherein R.sub.1 is H or methoxy, R.sub.2 is H, methoxy, OH or F, R.sub.3 is H or F, R.sub.4 is H or F at 7-, 8- or 9-position, and .circle.Ar is a benzene, thiophene or pyridine ring, provided that (i) at least two of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are H, (ii) R.sub.2 or R.sub.3 is F when R.sub.4 is F, (iii) R.sub.1, R.sub.3 and R.sub.4 are H when R.sub.2 is methoxy or OH, (iv) R.sub.2 and R.sub.3 are not simultaneously F, and (v) R.sub.2 and R.sub.3 are H or F, and both R.sub.1 and R.sub.4 are H when .circle.Ar is a thiophene or pyridine ring, or a physiologically acceptable acid addition salt thereof. The compounds of the present invention have an excellent protective effect against cerebral anoxia and some of them have also an inhibitory effect on lipid peroxidation of mitochondrial membrane of brain and an anti-convulsant activity and are useful as an agent for prevention or treatment of cerebral diseases caused by hypoxia in mammals including human.