Compounds are disclosed of formula (I) ##STR1## wherein R.sub.1 represents a C.sub.1-6 alkyl group;R.sub.2 represents a hydrogen atom or a C.sub.1-3 alkyl group;n represents zero or an integer from 1 to 3;and pharmaceutically acceptable salts thereof.The compounds are useful for the treatment of migraine, cluster headache, chronic paroxysmal hemicrania and headache associated with vascular disorders.Processes and intermediates for their preparation and pharmaceutical compositions containing them are also disclosed.