Under nitrogen protection, 50 g (0.13 mol) pregnane-1,4,9(11)-triene-3,20-dione-17-hydroxy-21-acetate was added to a reaction vial with 200 mL of pyridine, cooled to -15 °C and stirred. Subsequently, 30 g of N-chlorosuccinimide (NCS) was added and 17.5 g (0.27 mol) of SO2 gas was slowly vented over a period of 1 h. The reaction temperature was controlled to not exceed -10°C. After completion of the venting, stirring was continued for half an hour. Upon completion of the reaction, the formation of a mixed solution containing δ16 steroidal compound (I) was confirmed by TLC monitoring. This mixed solution was poured into 300 mL of concentrated hydrochloric acid, 2000 mL of ice water was added, and left to stand for 2 hours to remove water-soluble impurities. After separating the aqueous layer, the organic layer was concentrated to get at least the amount of liquid, filtered to get a solid, and dried at 60 °C to obtain 47 g of δ16 steroidal compound (I). The purity of this δ16 steroidal compound (I) was 99% as determined by high performance liquid chromatography (HPLC).
