This invention pertains to compounds suitable for dyeing keratin fibers, especially human hair. The compounds have the formula: ##STR1## or an acid addition salt thereof, in which formula R.sub.1 and R.sub.2 form, together with the nitrogen atom to which they are bonded, a morpholino or piperidino ring and R represents a hydrogen atom.This invention also pertains to compositions for dyeing keratin fibers, especially human hair, such composition containing the compounds set forth above and/or compounds of formula (I) wherein R.sub.1 represents a hydrogen atom, R.sub.2 represents a tetrahydrofurfuryl or methoxyethyl radical and R represents a hydrogen atom or a methyl radical, or an acid addition salt thereof.The invention also pertains to the method of using these compositions.