Chroman derivative and pharmaceutical use thereof

A chroman compound of the formula ›I! ##STR92## wherein R.sup.1 is a cyano, a nitro, a trihalomethyl, a trihalomethoxy or a halogen atom;

• R.sup.2 is a lower alkoxyalkyl wherein the total carbon number of the alkoxy moiety and alkyl moiety is 2 to 6, a phenyloxy C.sub.1 -C.sub.5 alkyl or a dialkoxyalkyl having 3 to 8 carbon atoms;
• R.sup.3 is a lower alkoxyalkyl wherein the total carbon number of the alkoxy moiety and alkyl moiety is 2 to 6 or a phenyloxy C.sub.1 -C.sub.5 alkyl;
• R.sup.4 is a hydroxy, a formyloxy or a lower alkanoyloxy;
• X is N--H, an oxygen atom or a sulfur atom;
• and
• Y is a dihydrooxopyridazinyl or dihydrothioxopyridazinyl optionally substituted by 1 to 3 substituents selected from the group consisting of
• lower alkyl having 1 to 7 carbon atoms optionally monosubstituted by a substituent selected from the group consisting of nitro, halogen atom, cyano, lower alkoxy having 1 to 4 carbon atoms, cycloalkyl having 3 to 6 carbon atoms, lower alkylsulfonyl having 1 to 4 carbon atoms, lower alkylsulfinyl having 1 to 4 carbon atoms, carboxyl, di-lower alkylamino having 1 to 6 carbon atoms, alkylthio having 1 to 4 carbon atoms, benzyloxycarbonyl and lower alkoxycarboxyl having 2 to 5 carbon atoms:
• lower alkenyl having 2 to 4 carbon atoms:
• phenyl optionally mono-substituted by nitro and benzyl, or a pharmaceutically acceptable salt thereof.