Synthesis of 16-Fluoroestrogens by Unusually Facile Fluoride Ion Displacement Reactions: Prospects for the Preparation of Fluorine-18 Labeled Estrogens

16α-Fluoroestradiol and 16/3-fluoroestradiol can be prepared by the reaction of fluoride ion with the opposite corresponding epimeric [[(trifluoromethyl)sulfonyl]oxy]estrone precursors, followed by stereoselective reduction to the 17β-estradiols. The related 17β-ethynyl compounds can be prepared by ethynylation of the fluoroestrones. Stereochemical assignments, suggested by known reaction stereoselectivities, are supported by extensive ¹H and 19F NMR analyses. The fluoride ion displacement reactions operate rapidly and efficiently at room temperature, even with low concentrations of fluoride ion. This rapid and convenient fluorination method is adaptable to the preparation of fluorine-18 labeled estrogens that may be useful as breast tumor imaging agents.