A compound represented by the following formula (I) or a pharmaceutically acceptable salt thereof works as an mGluR2 antagonist, and is applicable as a therapeutic agent for neurological disorders related to glutamate dysfunction and diseases involving the mGluR2, such as Alzheimer's disease: wherein R is a hydrogen atom, a C1-6 alkyl group or the like, R1 is a C1-6 alkyl group, a C1-6 alkoxy group or the like, R2 is a halogen atom, a C1-6 alkyl group, a C1-6 alkoxy group or the like, R3 is a hydrogen atom, a C1-6 alkyl group or the like, and R4 is a C1-6 alkyl group or the like.由以下式(I)所代表的化合物或其藥學上可接受的鹽作為mGluR2拮抗劑起作用並且可適用於作為用於涉及麩胺酸鹽機能障礙的神經障礙以及涉及mGluR2的疾病的治療劑，例如阿滋海默症：其中R係氫原子、C1-6烷基或者類似物，R1代表C1-6烷基、C1-6烷氧基或者類似物，R2代表鹵素原子、C1-6烷基、C1-6烷氧基或者類似物，R3代表氫原子、C1-6烷基或者類似物，並且R4代表C1-6烷基或者類似物。
