Compounds are disclosed of formula (I) ##STR1## wherein R.sub.1 represents H or C.sub.1-6 alkyl;R.sub.2 represents H, C.sub.1-6 alkyl, C.sub.3-7 cycloalkyl, C.sub.3-6 alkenyl, phenyl or phen(C.sub.1-3)alkyl in which the phenyl ring is optionally substituted by halogen, C.sub.1-4 alkoxy, hydroxy or C.sub.1-3 alkyl;R.sub.3 represents H, C.sub.1-3 alkyl, --CO.sub.2 R.sub.5, --COR.sub.5, --COCO.sub.2 R.sub.5 or --CONHR.sub.5 whereR.sub.5 represents H, C.sub.1-4 alkyl, C.sub.3-7 cycloalkyl, C.sub.2-4 alkenyl, aryl or ar(C.sub.1-4)alkyl in which the aryl group is optionally substituted by halogen, C.sub.1-4 alkoxy, C.sub.1-4 alkyl or hydroxy) (provided that where R.sub.3 represents --CO.sub.2 R.sub.5, R.sub.5 is other than H);R.sub.4 represents H, C.sub.1-3 alkyl, C.sub.3-6 alkenyl, phenyl or phen (C.sub.1-3)alkyl;A-B represents CH--CH.sub.2 --or C.dbd.CH--D represents --CO-- or --SO.sub.2 --n represents 0, 1-5;provided that when D represents --SO.sub.2, n is 2, R.sub.3 represents H and R.sub.4 represents H or C.sub.1-3 alkyl, R.sub.2 is other than H or C.sub.1-6 alkyl; and pharmaceutically acceptable salts and solvates (for example hydrates) thereof.The compounds are indicated as 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.