11β-Ethyl-17β-dodecyloxycarbonyloxyestr-4-en-3-one (9b, CDB-4722) was prepared as follows: Under nitrogen, a solution of 11β-ethylestr-4-en-17β-ol (7b, 0.1 g, 0.33 mmol) in dry CH2Cl2 (5 mL) was cooled to 0° C. in an ice bath. Pyridine (0.1 mL, 97.8 mg, 1.24 mmol) followed by dodecyl chloroformate (0.2 mL, 1.84 mg, 0.74 mmol) were added and the mixture stirred at 0° C. for 15 min and then allowed to warm to room temperature. The reaction was stirred at room temperature overnight, after which time, TLC (2% acetone in CH2Cl2) indicated a complete reaction. The mixture was diluted with additional CH2Cl2 (50 mL) and washed with water (1×), saturated sodium bicarbonate solution (1×), and water (1×). The organic fractions were filtered through anhydrous Na2SO4, combined and concentrated in vacuo to give 0.3 g residue as a clear oil. This crude material was purified by Flash chromatography (2% acetone in CH2Cl2) to give 0.16 g of a clear oil in 94% yield, which resisted crystallization.
