A compound of the formula: ##STR1## wherein R.sup.1 is a C.sub.1 -C.sub.6 alkyl group and R is a hydrogen atom or a C.sub.1 -C.sub.6 alkyl group, and their salts, which are useful as cerebral vasodilator; and a compound of the formula: ##STR2## wherein R.sup.2 is a hydrogen atom or a C.sub.1 -C.sub.6 alkyl group, R.sup.3 is a hydrogen atom or the formula: --CO.sub.2 R.sup.1 (R.sup.1 is a C.sub.1 -C.sub.6 alkyl group) and W is an oxygen atom, an imino group or ##STR3## but not an imino group in case that R.sup.3 is a hydrogen atom, which are intermediates of the compound (I), useful per se as cerebral vasodilator and/or antihypertensive agents.