Abstract
1α-Fluorovitamin D3 has been synthesized from 6β-acetoxy-5α-cholest-1-en-3-one (2) via 1α-fluorocholesterol (11). The key reaction was the trans diaxial ring opening of the 1β, 2β-epoxide 5 with potassium hydrogen difluoride in ethyleneglycol by heating. The resulting 1α-fluoro-2β, 3β-diol was subjected to regeneration of the 5-ene function and reductive removal of the 2β-hydroxyl group by Barton's method to give 1α-fluorocholesterol (11). Transformation of 11 into 1α-fluorovitamin D3 led to revision of the previously reported stereochemical assignment of 1α, 25-difluorovitamin D3.
