Compounds of formula (I) ##STR1## in which R.sub.1 represents hydrogen, a C.sub.1-6 aliphatic hydrocarbyl group or a C.sub.1-4 aliphatic hydrocarbyl group substituted by a C.sub.3-6 alicyclic hydrocarbyl group or by a phenyl group, which phenyl group is unsubstituted or substituted by a halogeno or C.sub.1-3 halogenoalkyl group, R.sub.2 represents hydrogen, R.sub.3 represents hydrogen, a 5- or 6-membered ring aromatic heterocyclyl group containing one or two heteroatoms selected from nitrogen, oxygen and sulphur which is unsubstituted or substituted by a halogeno or C.sub.1-3 halogenoalkyl group, or a group AR wherein A is a straight chain C.sub.1-4 aliphatic hydrocarbyl group terminally substituted by R which is hydrogen, a phenyl group or a 5- or 6-membered ring aromatic heterocyclyl group containing one or two heteroatoms selected from nitrogen, oxygen and sulphur, which phenyl or heterocyclyl group R is unsubstituted or substituted by a halogeno or C.sub.1-3 halogenoalkyl group, R.sub.4 and R.sub.5 each represent hydrogen or together represent an oxo group and R.sub.6, R.sub.7 and R.sub.8 each represent hydrogen, or R.sub.4 represents hydrogen and two of R.sub.5, R.sub.6, R.sub.7 and R.sub.8 together represent the second bond of a double bond joining positions 4 and 5, 5 and 6 or 6 and 7 with the remaining two of R.sub.5, R.sub.6, R.sub.7 and R.sub.8 representing hydrogen, the compound optionally being in the form of a salt thereof formed with a physiologically acceptable inorganic or organic acid, are of value for the treatment of anxiety and in the improvement of learning and/or the reversal of amnesia.