Abstract: Compounds useful in the treatment of patients suffering from senile dementia, Alzheimer's disease or memory defects, of the formula ##STR1## in which R' represents hydrogen, a linear, branched or cyclic alkyl, alkenyl or alkynyl, containing up to 8 carbon atoms, and R represents a linear, branched or cyclic alkyl, alkenyl, or alkynyl, containing up to 18 carbon atoms, possibly substituted, aryl containing up to 14 carbon atoms, possibly substituted, aralkyl containing up to 18 carbon atoms, possibly substituted, as well as their addition salts with organic or mineral acids, and to compounds of formula (I) in which R represents phenyl substituted in the 4 position by Br, F, CH.sub.3, NO.sub.2 or C(CH.sub.3).sub.2 C(CH.sub.3).sub.3 and R' represents CH.sub.3.