As an example, the synthesis of 17-iodo-androsta-5,16-dien-3β-ol (13) was carried out: iodine (12.16 g, 0.0203 mol) was dissolved in anhydrous THF (144 mL) and dry Et2O (72 mL), stirred and cooled to 0 °C in an ice bath. Subsequently, 1,1,3,3-tetramethylguanidine (6.72 mL, 6.24 g, 0.054 mol) was added to this solution. A THF (81 mL) solution of compound 12 (3.0 g, 9.9 mmol) was slowly added dropwise to the above iodine solution over a period of 2 hrs, ensuring that the reaction temperature was maintained at 0°C. Upon completion of the reaction, the mixture was concentrated under vacuum, cooled to ice bath temperature and then dried under vacuum at room temperature to give the yellow solid product 13 (3.65 g, 92.4% yield). The melting point of the product was 169-171 °C (literature value 175-176 °C); IR (CHCl3) showed absorption peaks located at 2935, 1371, 1039, 862, 843, 799, 715, 665, 582 and 566 cm-1 ; 1H NMR (300 MHz, CDCl3) δ value: 0.76 (s, 3H, 18-CH3), and 1.05 (s, 3H, 19-CH3), 3.50 (br s, 1H, 3α-H), 5.35 (s, 1H, 6-H) and 6.14 (s, 1H, 16-H).
