Chemical isomerization and its isomerization course of vitamin D_2 by boron trifluoride or antimony trichloride (reported by Inhoffen, et al. and Kodicek, et al.) were investigated by using the previously reported alumina-column chromatographic and gas chromatographic procedures. It was confirmed that vitamin D_2 was isomerized to isotachysterol_2 by the both reagents through the following course : vitamin D_2→isocalciferol→isotachysterol_2.
