In order to examine the vitamin D activity, 4, 4-dimethylcholecalciferol (IV), m.p. 71∼73°, [α]D +23.7°, was prepared by irradiation of ultraviolet rays on 4, 4-dimethyl-7-de-hydrocholesterol (V). Pyrolysis reaction of (IV) was found to result in preferential cyclization to pyrocalciferol-type compound and 4, 4-dimethyl-10-isocholesta-5, 7-dien-3β-ol (XI), m.p. 71∼73°, [α]D +543°, was obtained in a good yield.
