Compounds are disclosed of formula (I) ##STR1## wherein R.sub.1 represents --COR.sub.4, --CO.sub.2 R.sub.4 or --COCO.sub.2 R.sub.4 (where R.sub.4 represents a hydrogen atom or an unsubstituted or substituted C.sub.1-10 hydrocarbon moiety); R.sub.2 and R.sub.3 are the same or different and are C.sub.1-6 alkyl or C.sub.3-6 alkenyl; or --NR.sub.2 R.sub.3 forms a 5-membered (optionally containing an oxygen atom adjacent to the nitrogen) or 6-membered ring, which ring optionally contains one unit of unsaturation and which is unsubstituted or substituted by optionally substituted methylidene, --COR.sub.5 (where R.sub.5 represents C.sub.1-6 alkyl, --OR.sub.6 or --NHR.sub.6 and R.sub.6 represents hydrogen, C.sub.1-6 alkyl, aryl, or ar(C.sub.1-6)alkyl, or N.dbd.NOR.sub.7 (where R.sub.7 represents C.sub.1-6 alkyl); X represents a direct bond, --CH.sub.2 -- or --CH.sub.2 O--; Ar represents a substituted phenyl moiety; and physiologically acceptable salts thereof. The compounds are indicated as useful in the treatment of pain and cerebral ischaemia. Processes and intermediates for their preparation and pharmaceutical compositions containing them are also disclosed.