Compounds of the formula I in which R1, R2, R3 and R4 are as defined in claim 1, are ligands of the nicotinic acetylcholine receptor and/or serotonergic ligands and are suitable for the prophylaxis or treatment of psychoses, schizophrenia, depression, anxiety states, dementia, in particular Alzheimer's disease and Lewy bodies dementia, neurodegenerative disorders, Parkinson's disease, amyotrophic lateral sclerosis, Huntington's disease, Tourette's syndrome, learning and memory restrictions, bulimia anorexia nervosa or other eating disorders, compulsvie behaviour, premenstrual syndrome, age-induced memory impairment, amelioration of withdrawal symptoms in nicotine dependence, strokes or brain damage by toxic compounds, and for the treatment of disorders which are characterised by an excess of circulating serotonin or by serotonergic hyperactivity