Potassium isolespedezate (1) is a leaf-opening factor controlling the nyctinastic leaf-movement of leguminous plants. We carried out bioorganic studies on nyctinasty by using synthetic probes designed on the structure of 1 and its galactose analog (2). However, 1 was synthesized via an indirect route because of the difficulty of direct formation of the enol-glycosidic linkage. More efficiency is desired for the preparation of 1 and 2 which are necessary for the synthesis of probe compounds. In this paper, we report the biomimetic synthesis of 1 containing direct formation of an enol-glucosidic linkage. This efficient route makes it possible to prepare 1 and 2 in large quantity.