An Alternative and Efficient Synthesis of 24,24-Difluoro-1.ALPHA.,25-dihydroxyvitamin D3

An alternative synthesis of the title compound 2, a highly potent analog of 1α, 25-dihydroxyvitamin D3 (1), is described. Starting with 1α, 3β-bis[(tert-butyldimethylsilyl)oxy]androst-5-ene (8), 2 was obtained in 3.8% total yield through 10 steps. This method provides compound 2 in much higher yield than that reported previously.