A compound selected from those of formula (I): ##STR00001## wherein: X represents a C(O) or SO.sub.2 group, R.sub.1 represents an aryl group or a group NR.sub.3R.sub.4 wherein R.sub.3 and R.sub.4 are as defined in the description, R.sub.2 represents an alkyl, (C.sub.3-C.sub.8)cycloalkyl or (C.sub.3-C.sub.8)cycloalkyl-(C.sub.1-C.sub.6)alkyl group, its isomers, and addition salts thereof, and medicinal products containing the same which are useful in treating conditions treatable by antagonists of type H.sub.3 central histamine receptors.