Cholesterol (7.76 mmol, 3.0 g) and triphenylphosphine (7.76 mmol, 2.04 g) were dissolved in 77.6 mL of anhydrous tetrahydrofuran. Diisopropyl azodicarboxylate (7.76 mmol, 1.5 mL) was then added dropwise. After stirring the orange mixture for a few minutes, diphenylphosphoryl azide (7.76 mmol, 1.68 mL) was added dropwise. After 24 hours, the pale yellow reaction mixture was concentrated. Purification by silica gel chromatography (100% hexanes) afforded 3α-azidocholest-5-ene (2.14 g, 67%) as a white solid. mp 110-112° C.; TLC Rf=0.87 (20% ethyl acetate/hexanes); IR (thin film) 2946, 2914, 2845, 2083 cm−1; 1H NMR (300 MHz, CDCl3) δ 5.42-5.40 (m, 1H), 3.89 (t, 1H, J=2.9 Hz), 2.58-2.49 (m, 1H), 2.23-2.16 (m, 1H), 2.16-1.93 (m, 2H), 1.89-1.05 (m, 24H), 1.02 (s, 3H), 0.93 (d, 3H, J=6.5 Hz), 0.88 (d, 6H, J=6.6 Hz), 0.69 (s, 3H).
