The photoisomerization of ergosterol to previtamin D₂, followed by thermal conversion to vitamin D₂ (VD₂), has been studied intensively. Lumisterol₂ is one of the byproducts, which is an important intermediate for preparation of hormone analogs such as 6-dehydro-9(beta),10(alpha)- progesterone.

To maximize the yield of lumisterol₂, a detailed study of photochemistry of ergosterol has been carried out, which shows that one pot direct irradiation procedure could be applied on a preparative scale. The irradiation of ergosterol solution with >283 nm light gave 17.2% previtamin₂, 25% lumisterol₂, 1.8% tachysterol₂, and 56% ergosterol (HPLC). Recrystallization from methanol gave pure lumisterol₂ in the yield of 75% based on the consumed ergosterol. The isolation procedure should be performed below 30ºC to prevent previtamin₂ from going to VD₂, because we found that lumisterol₂ and VD₂ can form 1:1 complex, which would cause a difficulty in lumisterol₂ isolation and lower the yield of lumisterol₂.