A compound represented by the formula (I): wherein R1 is an oxo group, ═N—R or the like; a group represented by the formula: is a group represented by the formula: R2 is a group represented by the formula: R3 and R4 are each H, or C1-C6 alkyl, C3-C6 cycloalkyl, C1-C6 alkoxy, C1-C6 alkylamino, di(C1-C6)alkylamino or C1-C6 alkylthio, each of which is optionally substituted; and R5 is H, or C1-C6 alkyl, C2-C6 alkenyl, cyclic group, each of which is optionally substituted, —CO—R8 or —O—R8′, or a salt thereof. The compound of the present invention is useful as a drug for the prophylaxis or treatment of circulatory diseases, metabolic diseases and/or central nervous system diseases.