Compounds of the general formula (I): wherein R<;SUP>;1<;/SUP>;, R<;SUP>;2<;/SUP>;, R<;SUP>;3 <;/SUP>;and R<;SUP>;4 <;/SUP>;are as described in the specification. Further included are pharmaceutical compositions comprising the compounds, processes for their preparation, as well as the use of the compounds for the preparation of a medicament which particularly acts on the central nervous system, particularly for use as anti-obesity agents.