Compounds of general formula [I] or pharmaceutically acceptable salts thereof; and agents for the treatment of hyperphagia, obesity or diabetes, comprising the same as the active ingredient wherein Ar1 is aryl or hetero-aryl which may be substituted with a radical selected from the group consisting of lower alkyl, lower hydroxyalkyl, lower alkylene and -NRaRb; R1 is hydrogen or lower alkyl; R?2 and R3¿ are each independently lower alkyl, or alternatively R?2 and R3¿ are united to form alkylene which may be interrupted by oxygen or sulfur and may be substituted with one or two lower alkyl radicals; R4 is hydrogen or lower alkyl which may be substituted with a radical selected from the group consisting of hydroxyl, amino, carbamoyl and lower alkoxycarbonyl; Ar2 is aryl or hetero-aryl which may be substituted with a radical selected from the group consisting of halogeno, hydroxyl, lower alkyl, lower haloalkyl, lower alkoxy, lower alkylthio, lower hydroxyalkyl, lower alkoxy lower alkyl, -NRcRcd and -NR?e-CO-NRfRg¿; and W is oxygen, sulfur, -CHRj- or -NRk-.