NEW MATERIAL:1alpha-Hydroxy-6-(1,3-benzodithiol-2-yl)oxy-3,5-cyclovitamin D3 expressed by formula I. USE:Useful as a synthetic intermediate for alfacalcidol (a drug, having action of increasing calcium in blood by absorption of calcium from the outside and mobilization of calcium from bones and useful for improving symptoms accompanied by vitamin D dysbolism). The alfacalcidol, i.e., 1alpha-hydroxyvitamin D3 is synthesized by solvolyzing the compound expressed by formula I in the presence of a beteropoly-acid. PREPARATION:For example, a compound expressed by formula II is reacted with 1,3-benzodithiolium tetrafluoroborate in the presence of a base, such as pyridine, in a solvent, such as dichloromethane, while being cooled with ice to afford a novel compound expressed by formula III, which is then subjected to allylic oxidation to provide the compound expressed by formula I.
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